USMLE 1 Q 11

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    (42) <1>An 18-year-old college student presents to the student health
    center complaining of a sore throat and fever. He describes feeling
    tired for the past few days and reports a loss of appetite. On
    examination, he has pharyngitis with cervical lymphadenopathy.
    Blood tests reveal lymphocytosis and the presence of heterophil
    antibodies. Which of the following best describes the virus
    responsible for his illness?
    A. Double-stranded, enveloped DNA virus
    B. Double-stranded, nonenveloped DNA virus
    C. Single-stranded, enveloped RNA virus
    D. Single-stranded, nonenveloped DNA virus
    E. Single-stranded, nonenveloped RNA virus

    Answer
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    <2>Which of the following organisms is a natural transformer?
    A. Escherichia coli
    B. Neisseria gonorrhoeae
    C. Plasmodium vivax
    D. Pseudomonas aeruginosa
    E. Staphylococcus aureus
    Answer
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    <3>A child psychiatrist would like to evaluate the intellectual
    ability of a 3-year-old patient. Which of the following is the
    most appropriate test for him to use?
    A. Denver Developmental Scale
    B. Stanford-Binet Scale
    C. WAIS-R
    D. WISC III
    E. WPPSI
    Answer
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    <4>A 57-year-old woman with a 30-year x 2 pack/day history of cigarette
    smoking undergoes bronchoscopy. Biopsy of bronchial tissue show
    s replacement of the normal pseudostratified ciliated columnar
    epithelium with stratified squamous epithelium. This change
    represents
    A. dysplasia
    B. hyperplasia
    C. malignant transformation
    D. metaplasia
    E. necrosis and repair
    Answer
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    <5>A 25-year-old woman presents to her physician with complaints of
    easy bruising and excessive bleeding. Physical examination demonstrates
    hepatosplenomegaly. A blood smear reveals pancytopenia and a bone marrow
    biopsy demonstrates markedly enlarged cells containing a fine fibrillar
    material resembling tissue paper. Leukocyte enzymatic studies demonstrate
    a deficiency of beta-D-glucosidase activity. Which of the following
    substances is most likely to accumulate in the bone marrow cells?
    A. Galactose
    B. Glucosylceramide
    C. Glycogen
    D. Homocysteine
    E. Mineralocorticoids
    Answer
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    <6>A 34-year-old HIV-positive man without previous opportunistic
    infections presents complaining of dyspnea with daily activity. He
    states that he has had a mild cough and fever but denies having had
    chills, sputum production, or chest discomfort. Physical examination
    is remarkable for oral thrush and a few small, nontender cervical
    lymph nodes. A chest x-ray film reveals bilateral interstitial
    infiltrates, and bronchoalveolar lavage reveals small silver-staining
    cysts. In which other patient population in the U.S. is this organism
    a frequent cause of a life-threatening pneumonia?
    A. Bone marrow transplant patients
    B. Hospitalized adults on antibiotic therapy
    C. Late-term pregnant women
    D. Normal adults in periods of stress
    E. Premature infants
    F. Preschool children
    G. Sexually active adolescents
    H. Third-trimester fetuses
    Answer
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    <7>A 28-year-old HIV-positive male complains of pain on swallowing.
    Physical examination is remarkable for white plaque-like material
    on his tongue and buccal mucosa, which is scraped and sent to the
    laboratory. Based on these findings, and on the laboratory results
    , the man is diagnosed with acquired immunodeficiency syndrome (AIDS).
    With which of the following agents is the man most likely infected?
    A. Candida albicans
    B. Cytomegalovirus
    C. Herpes simplex I
    D. Human herpesvirus 8
    E. Human papilloma virus
    Answer
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    <8>A superantigen is a bacterial product that
    A. binds to B7 and CD28 costimulatory molecules
    B. binds to the b chain of TCR and MHC class II molecules of APC stimulating T cell activation
    C. binds to the CD4 + molecule causing T cell activation
    D. is presented by macrophages to a larger-than-normal number of T helper CD4 + lymphocytes
    E. stimulates massive amounts of IgG synthesis because of its large size
    Answer
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    <9>A young adult has progressive intellectual deterioration, weakness,
    ataxia, and seizures. Reference laboratory tests demonstrate an
    abnormality of an important mitochondrial enzyme. From which of
    the following diseases is this person most likely suffering?
    A. Adrenoleukodystrophy
    B. Central pontine myelinolysis
    C. Krabbe's disease
    D. Leigh's disease
    E. Metachromatic leukodystrophy
    Answer
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    <10>During a bitterly cold winter, an elderly couple is found dead in
    their apartment. All of their windows are closed and their leaky old
    furnace is on full. Which of the following is the primary mechanism
    by which the toxin involved led to the death of this couple?
    A. Decreasing intracellular calcium
    B. Inhibition of cytochrome oxidase
    C. Inhibition of Na+/K+ ATPase
    D. Irreversibly binding to hemoglobin
    E. Stimulation of cellular apoptosis
    Answer
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    <11>A child has a history of recurrent infections with organisms having
    polysaccharide antigens (i.e., Streptococcus pneumoniae and Hemophilus
    influenzae). This susceptibility can be explained by a deficiency of
    A. C3 nephritic factor
    B. C5
    C. IgG subclass 2
    D. myeloperoxidase in phagocytic cells
    E. secretory IgA
    Answer
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    <12>A 32-year-old medical technician had a history of acute eczematous
    dermatitis on her hands and wrist in the distribution of the latex gloves
    she wore. The skin of her hands was dry, crusted, and thickened. The
    eczematous reaction cleared after a 2-week vacation. After 72 hours
    back on the job, the eczematous dermatitis returned and continued to
    grow worse. Which of the following characterizes the technician's
    reaction to the latex gloves?
    A. Irritant dermatitis
    B. Type I reaction
    C. Type II reaction
    D. Type III reaction
    E. Type IV reaction
    Answer
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    <13>Cytotoxic T cells induced by infection with virus A will kill target
    cells
    A. from the same host infected with any virus
    B. infected by virus A and identical at class I MHC loci to the cytotoxic T cells
    C. infected by virus A and identical at class II MHC loci to the cytotoxic T cells
    D. infected with any virus and identical at class I MHC loci to the cytotoxic cells
    E. infected with any virus and identical at class II MHC loci to the cytotoxic cells
    Answer
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    14 .A 22-year-old female college student is brought into
    the emergency room by the police, who found her walking back
    and forth across a busy street, talking to herself. The young
    woman appears to be oriented with respect to person, place,
    and time. Her first hospital admission was two months ago
    for a similar condition. During a psychiatric interview,
    she has difficulty concentrating, and seems to hear voices.
    A phone call to her sister provides the additional information
    that the girl dropped out of school three months ago and has been
    living on the street. Urine toxicology is negative. This patient
    is most likely exhibiting the signs and symptoms of
    A. schizoaffective disorder
    B. schizoid personality disorder
    C. schizophrenia
    D. schizophreniform disorder
    E. schizotypal personality disorder
    Answer
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    <15>A 4-month-old male presents with twitching of the facial muscles.
    He has previously been seen for several severe episodes of Candida
    infections. On examination, the child has low-set ears, hypertelorism,
    and a shortened philtrum. What additional findings would be likely in
    this individual?
    A. Absent thymic shadow on chest x-ray
    B. Decreased alpha-fetoprotein
    C. Decreased IgA levels
    D. Elevated IgM levels
    E. Prominent telangiectasias around the eyes
    Answer
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    <16>A 16-year-old high school cheerleader presents with low grade fever,
    pleuritic pain and a non-productive cough. Her serum agglutinates
    Streptococcus salivarius strain MG. Therapy should include which of
    the following?
    A. Ampicillin
    B. Erythromycin
    C. Oxygen and external cooling
    D. Penicillin G
    E. Ribavirin
    Answer
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    <17>A 55-year-old male begins group therapy. After the first session, he
    befriends one of the other clients, and begins telling her how
    extraordinarily intelligent and talented the facilitator is. At
    the next session, he and the facilitator disagree. After the
    session, he tells his fellow group member that the facilitator
    is utterly incompetent and that they should sue for malpractice.
    This is an example of
    A. displacement
    B. fixation
    C. reaction formation
    D. regression
    E. splitting
    Answer
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    <18>A 5-year-old girl is brought by her parents to the emergency room
    because she is complaining of stomach pain. Physical examination reveals
    multiple bruises on the child's body in different stages of healing.
    X-ray examination of the chest demonstrates two cracked ribs, and the
    child says, "Mommy hit me." The parents deny any abuse of their
    children. The physician's most appropriate response would be:
    A. "I am going to call the police right now."
    B. "I must report this situation to Child Protective Services right now."
    C. "I need to hospitalize this child for further studies."
    D. "I will bind her ribs tonight and you must promise me that you will not strike this child again."
    E. "I will bind her ribs tonight and you need to bring her to the outpatient clinic in the morning."
    Answer
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    <19>A 20-year-old woman sees her baby cousin for the first time. As she
    attempts to play with the infant, he begins to cry incessantly. How old
    is this baby likely to be?
    A. 1-4 months
    B. 5-8 months
    C. 9-12 months
    D. 13-16 months
    E. 17-20 months
    Answer
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    <20>An IgG2 molecule is composed of which of the following?
    A. One alpha, one gamma2, and two kappa chains
    B. One gamma1 chain and two kappa chains
    C. Two gamma1 chains and one kappa and one lambda chain
    D. Two gamma1 chains and two kappa chains
    E. Two gamma2 chains and two kappa chains
    Answer
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    <21>Which of the following is the most important costimulatory signal
    provided to a T cell from an antigen-presenting cell?
    A. B7 molecules interacting with CD 28
    B. B7 molecules interacting with LFA- 1
    C. ICAM-I interacting with LFA-1
    D. LFA-3 interacting with CD 28
    E. MHC class II interacting with T cell receptor
    Answer
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    <22>A febrile 12-year-old child presents with severe right lower quadrant
    pain that is interpreted by the attending physician as acute appendicitis.
    The patient has also been complaining of joint pain. At laparotomy, the
    surgeon notes that the appendix is normal; however, the mesenteric lymph
    nodes are markedly enlarged and contain focal areas of microabscess
    formation on cut section. This patient is most likely
    A. an asthmatic
    B. deficient in C1 esterase inhibitor activity
    C. HLA-B27 positive
    D. leukopenic
    E. serologically positive for toxoplasmosis
    Answer
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    <23>1. Degranulation of mast cells and basophils occurs when allergen binds
    to two adjacent IgE antibodies on the membrane of the cell 2. Interleukin
    4 released by CD4 helper T cells causes activated B cells to switch from
    making IgM to IgE 3. Processed allergen is associated with a class II
    molecule on an antigen presenting cell and recognized by CD4+ TH2 cells
    4. Prostaglandins and leukotrienes are released 5. The allergen is
    phagocytized and processed by a macrophage or a dendritic cell
    Based on the numbered list above, which of the following is the
    correct sequence of events in the Type I hypersensitivity reaction?
    A. 1,2,3,5,4
    B. 1,4,3,5,2
    C. 1,5,2,3,4
    D. 5,3,1,4,2
    E. 5,3,2,1,4
    Answer
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    <24>An antibiotic, such as penicillin, which modifies cell wall synthesis,
    tends to be most effective during which phase of bacterial growth in a
    closed system?
    A. Lag phase
    B. Log phase
    C. Phase of decline
    D. Stationary phase
    Answer
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    <25>A 57-year-old woman with a history of hypertension and arthritis is
    referred to a rheumatologist for evaluation. A complete blood count
    (CBC) is normal, and a mini-chem panel shows no electrolyte abnormalities.
    Her erythrocyte sedimentation rate (ESR) is elevated, and an antinuclear
    antibody test (ANA) is positive. Further antibody studies are performed,
    and the results are shown below.
    Anti-histones high titer
    Anti-double stranded DNA not detected
    Anti-single stranded DNA not detected
    Anti-SSA not detected
    Anti-SSB not detected
    Anti-SCI-70 not detected
    Anti-Smith not detected
    Anit-centromere not detected
    Anti-RNP not detected
    Which of the following diseases is suggested by these results?
    A. CREST syndrome
    B. Diffuse form of scleroderma
    C. Drug-induced lupus
    D. Sjِgren's syndrome
    E. Systemic lupus erythematosus
    Answer
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    <26>A 65-year-old woman is evaluated for symmetrical swelling of the proximal phalangeal joints. Physical examination also reveals large subcutaneous nodules over the extensor surfaces of both arms. Autoantibodies directed against which of the following antigens would most likely be demonstrated by serum studies?
    A. Acetylcholine receptor
    B. Double stranded DNA
    C. Histones
    D. IgG
    E. Ribonucleoprotein
    Answer
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    <27>A 6-year-old boy presents to the pediatric clinic with fever and earache. He has just finished an unsuccessful course of amoxicillin. On physical exam, his right tympanic membrane appears injected. Which of the following antimicrobials would be most appropriate to prescribe for this patient?
    A. Amphotericin B
    B. Bacitracin
    C. Cefaclor
    D. Erythromycin
    E. Sulfamethoxazole
    Answer
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    <28>A 33-year-old woman is brought into the emergency room by ambulance.
    She has been diagnosed as having schizophrenic disorder, disorganized
    type, since the age of 17. She has been on antipsychotic medications
    since that time, which have controlled her symptoms well. Physical
    examination reveals a well-nourished female with a temperature of
    103.2 degrees F, BP of 180/99, HR of 97, and copious perspiration.
    She is mute, has muscular rigidity and appears to be obtunded.
    Which of the following is the most likely diagnosis?
    A. Acute dystonia
    B. Akathisia
    C. Neuroleptic malignant syndrome
    D. Parkinsonism
    E. Tardive dyskinesia

    <29>In a closed system, spores are formed during which of the following
    phases of bacterial growth?
    A. Decline phase
    B. Exponential phase
    C. Lag phase
    D. Log phase
    E. Stationary phase
    Answer
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    <30>A 14-year-old boy is brought to the emergency department by his
    parents because of high fever, headache, and stiff neck for the past
    36 hours. He has become confused over the course of the morning. He
    uses no medications, has no allergies, and is not sexually active.
    On examination, he has a temperature of 38 C, moderate nuchal
    rigidity, and marked photophobia. Lumbar puncture is performed,
    and the cerebrospinal fluid shows: WBC 3500 with 95% PMNs, elevated
    protein, decreased glucose, and gram-positive cocci in pairs and
    short chains. By which of the following mechanisms does this
    organism mediate its attachment to the respiratory mucosa?
    A. Production of a C carbohydrate
    B. Production of a hemolytic exotoxin
    C. Production of a hyaluronic acid capsule
    D. Production of an IgA protease
    E. Production of an M protein
    Answer
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    <31>A 46-year-old woman presents with complaints of feeling as if she
    has "sand in her eyes" and reports difficulty swallowing such foods
    as crackers or toast. Which of the following pairs of tests would
    likely yield positive results in this patient?
    A. Anti-centromere antibody and rheumatoid factor
    B. Anti-Scl-70 antibody and anti-Smith antibody
    C. Anti-Smith antibody and anti-double stranded DNA antibody
    D. Rheumatoid factor and anti-double stranded DNA
    E. Rheumatoid factor and anti-SS-A antibody
    Answer
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    <32>A viral organism was isolated from a painful blister on the lip of
    a teenage girl. The agent was found to double-stranded, linear DNA and
    was enveloped. The patient had a similar sore approximately 2 months
    ago. Which of the following is the most likely causative organism?
    A. Adenovirus
    B. Coxsackie virus
    C. Herpes simplex type 1 virus
    D. Herpes zoster virus
    E. Papilloma virus
    Answer
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    <33>A British dairy farmer develops fever with chills, myalgias, headache,
    skin rash, and vomiting. He is quite ill and is hospitalized. Blood
    cultures demonstrate tightly coiled, thin, flexible spirochetes shaped
    like a Shepherd's crook. The spirochetes are easily cultured in
    serum-enriched nutrient agar. Which of the following organisms
    should be suspected?
    A. Brucella abortus
    B. Brucella melitensis
    C. Leptospira interrogans
    D. Pseudomonas mallei
    E. Pseudomonas pseudomallei

    <34>A hospitalized patient develops dysuria and suprapubic pain and is
    treated with ciprofloxacin. What is the mechanism of action of this
    antibiotic?
    A. It inhibits dihydrofolate reductase
    B. It inhibits DNA-dependent RNA polymerase
    C. It inhibits protein synthesis by binding to the 30s ribosomal subunit
    D. It inhibits protein synthesis by binding to the 50s ribosomal subunit
    E. It inhibits topoisomerase II (DNA gyrase)
    Answer
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    <35>A 58-year-old alcoholic man with multiple dental caries develops a
    pulmonary abscess and is treated with antibiotics. Several days later,
    he develops nausea, vomiting, abdominal pain, and voluminous green
    diarrhea. Which of the following antibiotics is most likely responsible
    for this patient's symptoms?
    A. Chloramphenicol
    B. Clindamycin
    C. Gentamicin
    D. Metronidazole
    E. Vancomycin
    Answer
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    <36>A 36-year-old farmer has been exposed to poison ivy on several
    different occasions and usually develops very severe skin lesions.
    He enrolls in an immunological study at an urban medical center. A
    flow cytometric measurement of T cells reveals values within the
    normal range. An increased serum concentration of which of the following
    cytokines would decrease the likelihood of a delayed-type hypersensitivity
    reaction in this individual?
    A. Gamma interferon
    B. IL-2
    C. IL-4
    D. IL-8
    E. IL-10
    Answer
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    <37>A 22-year-old male is evaluated for mitral regurgitation due to mitral
    valve prolapse. Examination reveals a tall, slender young man with long
    extremities and long tapering fingers. Pupillary dilation followed by
    slit-lamp examination reveals bilateral dislocation of the lenses of
    the eyes. This patient is potentially at increased risk for development
    of
    A. aortic dissection
    B. Lisch nodules
    C. noncaseating granulomata
    D. progressive dementia
    E. rapidly progressive renal failure
    Answer
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    <38>A 57-year-old man is seen in clinic for a chronic cough. Chest x-ray
    demonstrates a lung mass; bronchoscopy with bronchial lavage and biopsy
    reveals a tumor composed of small neoplastic cells with prominent crush
    artifact that do not stain with immunohistochemical stains for lymphocyte
    common antigen (LCA). Which of the following oncogenes has been
    associated with this tumor?
    A. bcl-2
    B. erb-2
    C. L-myc
    D. N-myc
    E. ret
    Answer
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    <39>Which of the following features characterizes apoptosis but not
    necrosis?
    A. Disaggregation of polyribosomes
    B. Eosinophilia
    C. Inflammation
    D. Karyolysis
    E. Peripheral aggregation of chromatin
    Answer
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    <40>A woman who is heterozygous for glucose-6-phosphate dehydrogenase
    (G6PD), a polymorphic enzyme transcribed from the X chromosome, develops
    chronic myeloid leukemia. Restriction fragment length polymorphism (RFLP)
    studies on the tumor cells for G6PD reveal that only a single form of the
    enzyme is transcribed. This finding supports which of the following
    features of neoplasia?
    A. Genetic mutation
    B. Monoclonality
    C. Mosaicism
    D. Oncogene activation
    E. Point mutation
    Answer
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    <41>What is the role of the macrophage during antibody formation?
    A. Activation of cytotoxic CD8 T cells
    B. Delayed hypersensitivity reaction
    C. Lysis of virus-infected cells
    D. Processing antigen and presenting it to T helper CD4 cells
    E. Synthesis of immunoglobulin
    Answer
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    <42> The patient shown in the pedigree above did poorly in school,
    then became increasingly forgetful and irrational. Over a period of
    years, he developed ataxia and began posturing. Eventually, he was
    demented and unable to care for himself. At autopsy, extensive cortical
    demyelination is observed. Microscopic examination of the areas of
    demyelination reveals numerous macrophages containing crystals that
    stain a light brown color with toluidine blue. This presentation is
    probably due to a deficiency of
    A. arylsulfatase A
    B. galactocerebroside b-galactosidase
    C. glucocerebrosidase
    D. hexosaminidase A
    E. sphingomyelinase
    Answer
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    <43>A 46-year-old female with rheumatoid arthritis develops progressively
    worsening renal failure. She undergoes diagnostic renal biopsy, revealing
    thickening of the mesangial matrix and widened capillary basement
    membranes due to deposition of an amorphous, eosinophilic material
    that stains with Congo red. The material is shown to be composed of
    AA (amyloid-associated) protein fibrils. In which of the following
    locations is this protein synthesized?
    A. Bone marrow
    B. Brain
    C. Liver
    D. Synovium
    E. Thyroid
    Answer
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    <44>A 38-year-old woman complains of cold, painful fingertips, as well
    as difficulty swallowing and indigestion. Physical examination is
    remarkable for a thickened, shiny epidermis over the entire body,
    with restriction of movement of the extremities, particularly the
    fingers, which appear claw-like. Which of the following autoantibodies
    is likely to be found in this patient's serum?
    A. Anti-DNA topoisomerase I (anti-Scl-70)
    B. Anti-double-stranded DNA (ds DNA)
    C. Anti-IgG
    D. Anti-Sm
    E. Anti-SS-A
    Answer
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    <45>A 67-year-old male smoker presents to his physician for a routine
    physical examination. Chest x-ray demonstrates a 2-cm density on the
    left side. Laboratory studies are remarkable for a serum sodium of
    134 mEq/L. The findings may be attributable to tumor cell secretion
    of
    A. adrenocorticotrophic hormone (ACTH)
    B. antidiuretic hormone (ADH)
    C. melanocyte-stimulating hormone (MSH)
    D. parathyroid hormone (PTH)
    E. vasoactive intestinal polypeptide (VIP)
    Answer
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    <46>A 28-year-old mother gives birth to her first child. The father
    is homozygous Rh D positive and the mother is homozygous Rh D negative.
    The baby is born without any complications, but the mother is not given
    RhoGAM (anti-Rh IgG) following the delivery. Eighteen months later she
    delivers another child, who is anemic, slightly jaundiced, and has an
    enlarged spleen and liver. Which type of hypersensitivity best
    describes this condition?
    A. Atopic disease
    B. Cytotoxic disease
    C. Delayed hypersensitivity
    D. Immediate hypersensitivity
    E. Immune complex disease
    Answer
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    <47>A 24-year-old female has fever, malaise, and a dry, nonproductive
    cough. She also complains of headache, muscle aches, and leg pain. Lab
    values are significant for elevated cold agglutinins. Which of the
    following microorganisms is responsible for her symptoms?
    A. Haemophilus influenzae
    B. Klebsiella pneumoniae
    C. Legionella pneumophila
    D. Mycoplasma pneumoniae
    E. Streptococcus pneumoniae
    Answer
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    <48>A 29-year-old news correspondent returns from covering an earthquake
    and its aftermath in a third world country. The man feels tired and has
    sore muscles, so he consults a physician, who examines him, but decides
    not to admit him to the hospital. The man subsequently develops a
    disabling illness complicated by severe anemia, pulmonary edema,
    renal failure, and shock. Which of the following organisms is the
    most likely pathogen?
    A. Babesia microti
    B. Plasmodium falciparum
    C. Plasmodium malariae
    D. Plasmodium ovale
    E. Plasmodium vivax
    Answer
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    <49>A 12-year-old boy has a productive cough characterized by large
    volumes of foul-smelling sputum. Three years ago, the patient was
    diagnosed with pancreatic insufficiency, as evidenced by repetitive
    gastrointestinal symptoms of steatorrhea. After culture of the sputum,
    colorless, oxidase-positive colonies with a fruity aroma develop on the
    agar. The function of which of the following proteins is most likely
    inhibited by the bacteria responsible for this boy's infection?
    A. A CFTR protein lacking a phenylalanine in exon 10 at position 508
    B. A GTP-binding protein involved in the elongation step of protein synthesis
    C. A GTP-binding protein similar to the one coupled with a2-adrenergic receptors
    D. A GTP-binding protein similar to the one coupled with b-adrenergic receptors
    E. A phosphorylation-regulated chloride channel in the apical membrane of epithelial cells
    Answer
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    <50>Which of the following genes involved in the synthesis of
    immunoglobulins are linked on a single chromosome?
    A. C gene for gamma chain and C gene for alpha chain
    B. C gene for gamma chain and C gene for kappa chain
    C. V gene for kappa chain and C gene for the epsilon chain
    D. V gene for lambda chain and C gene for kappa chain
    E. V gene for lambda chain and V gene for heavy chain

    Answer
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    Answers
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    1>The correct answer is A. This is one of those USMLE-style items where figuring out the diagnosis is the easy part and remembering the basic science details is much tougher. In this case, the patient has all the hallmarks of mononucleosis (the heterophil antibodies should have confirmed your suspicion from the history and physical). Mononucleosis is caused by the Epstein-Barr virus, which, in turn, belongs to the herpesvirus family. The herpesviruses are enveloped viruses with double-stranded DNA. Remember that in addition to Epstein-Barr virus, the herpesvirus family also includes herpes simplex (1 and 2), varicella-zoster (chickenpox, shingles), and cytomegalovirus (infection in immunocompromised). Cytomegalovirus also causes infectious mononucleosis, but in these patients the heterophil test is negative.
    There are two families of viruses that are nonenveloped with double-stranded DNA (choice B): papovaviruses and adenoviruses.
    There are many families of viruses that are enveloped with single-stranded RNA (choice C): arenaviruses, bunyaviruses, coronaviruses, filoviruses, flaviviruses, paramyxoviruses, orthomyxoviruses, retroviruses, rhabdoviruses, and togaviruses.
    Parvoviruses are the only family of DNA virus with single-stranded DNA. They do not have an envelope (choice D).
    There are two families of RNA virus that are single-stranded without an envelope (choice E): caliciviruses and picornaviruses.

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    2>The correct answer is B. Transformation is the uptake and integration of naked DNA by a bacteria from the environment. Transformation can be induced in the laboratory (a technique used to introduce gene-carrying plasmids into bacteria) or, relatively uncommonly, occurs naturally. Only a few medically important species undergo natural transformation: Haemophilus species, Streptococcus species, Neisseria gonorrhoeae, and Helicobacter pylori.
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    3>The correct answer is B. The Stanford-Binet scale is best for younger children (2-4 years old), since it does not rely exclusively on language.
    The Denver Developmental Scale (choice A) is used to assess the attainment of developmental milestones in children under 2.
    The WAIS-R (Wechsler Adult Intelligence Scale; choice C) is used for individuals aged 17 and over. (Just think, the WAIS-R is rated "R").
    The WISC III (Wechsler Intelligence Scale for Children; choice D) is useful for evaluating children aged 6-16.
    The WPPSI (Wechsler Preschool and Primary Scale of Intelligence; choice E) is used for children aged 4-6.

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    4>The correct answer is D. Squamous metaplasia is a frequent airway response to chronic irritation from cigarette smoking. It represents the replacement of one differentiated tissue with another mature, differentiated tissue. It is believed that the squamous epithelium is more resistant to injurious agents, and so represents an adaptive response.
    Dysplasia (choice A) is characterized by pleomorphism (the individual cells may vary widely in appearance) and by loss of normal tissue architecture, rather than by replacement with another mature epithelium (squamous).
    Hyperplasia (choice B) refers to growth of a tissue or organ by cellular proliferation.
    Malignant transformation (choice C) is the multistep process by which normal cells progress to the "cancer" phenotype. Metaplasia is not malignant transformation, although the stimuli producing metaplasia may also be associated with the development of malignancy.
    Necrosis and repair (choice E) typically result in re-epithelialization and/or fibrosis, not metaplasia.
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    5>The correct answer is B. The disease is Gaucher disease, which is a glycolipid storage disease in which glucosylceramide accumulates in spleen, liver, and bone marrow. The defective enzyme, a lysosomal hydrolase known as acid beta-D-glucosidase, can be assayed in leukocytes separated from the blood by centrifugation. Interestingly, the defective enzyme can now be supplied intravenously, and strategies for transplantation of the cloned replacement gene are now being developed.
    Galactose (choice A) is a sugar. Deficiency of beta-D-glucosidase would not lead to accumulation of galactose.
    Glycogen (choice C) is a storage polymer of glucose. It accumulates in various glycogen storage diseases, but has a different appearance than the glycolipid in Gaucher disease.
    Homocysteine (choice D) is an amino acid. It does not accumulate in Gaucher disease.
    Mineralocorticoids (choice E) are lipids, but do not accumulate in bone marrow.


    6>The correct answer is E. This patient has Pneumocystis carinii pneumonia, the most common atypical pneumonia in AIDS patients. The next most common pool of at-risk individuals consists of premature infants.
    Bone marrow transplant patients (choice A) would be immunologically compromised, and might be a second at-risk group (behind premature infants), but would not be the first choice on this list.
    Hospitalized adults on antibiotic therapy (choice B) might be slightly immunologically compromised or stressed, but are not the major patient pool at risk for this infection in the U.S.
    Late-term pregnant women (choice C) are not immunologically compromised and would not be at risk.
    Normal adults in periods of stress (choice D) are not particularly susceptible to opportunistic pathogens.
    Preschool children (choice F) have normal rates of exposure to P. carinii, as would any adult, but are not susceptible to serious pneumonia with this agent unless they are immunologically suppressed.
    Sexually active adolescents (choice G) would have the same infection rates as normal infants and adults, but again would not be susceptible to life-threatening pneumonia. P. carinii is transmitted via aerosols, not sexual activity.
    Third-trimester fetuses (choice H) are not susceptible to infection with this fungus, although they may become infected in utero with HIV.
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    7>The correct answer is A. Candida albicans produces oral thrush, an AIDS-defining lesion, which is common in acute HIV disease, and becomes increasing common as the CD4 + cell count falls. The lesions are usually painless. Diagnosis is by demonstration of pseudohyphae using a wet smear with confirmation by culture.
    Although cytomegalovirus (choice B) is associated with numerous clinical scenarios in the AIDS population, including odynophagia (painful swallowing), it would not produce white plaques on the oral mucosa.
    Herpes Simplex I (choice C) produces vesicular lesions occurring in clusters in the oral cavity. There is an increased risk of herpes infections in the AIDS group, but the lesions do not resemble those described in the question.
    Human herpesvirus 8 (choice D) is the causative agent of Kaposi's sarcoma, a malignancy arising from endothelial cells that appears as hemorrhagic nodules in different organ systems. It is the most common cancer in the HIV infected population.
    Human papilloma virus (choice E) is associated with a variety of lesions, including warts and intraepithelial neoplasias of the vulva and cervix. It is associated with anal condyloma, which can occur in the AIDS population.
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    8>The correct answer is B. A superantigen, such as TSST- 1 or staphylococcal enterotoxin, cross-links the variable domain of the TCR b chain to the MHC class II molecule and specifically induces massive T cell activation.
    The superantigen does not bind the B7 and CD28 costimulatory molecules (choice A). Instead, the costimulatory molecules bind to each other to stimulate the reaction between the antigen-presenting cell and T cell.
    The superantigen does not bind the CD 4 molecules (choice C) but instead binds on the other side of the TCR receptor complex.
    The term superantigen has nothing to do with the antigen being presented by macrophages to T cells (choice D).
    The term superantigen has nothing to do with its size or its ability to stimulate antibody production (choice E). The term superantigen is used because of its unusual ability to create massive T cell activation by the unique type of binding.

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    9>The correct answer is D. Leigh's disease, also known as subacute necrotizing encephalomyelopathy, is a very rare disease that most physicians will never encounter in real life. However, it may show up on the USMLE because it is one of the few examples of diseases involving defects in the mitochondrial DNA rather than the chromosomal DNA. The specific defective enzyme, in at least some cases, is cytochrome oxidase, one of the components of the electron transport system. Muscle and brain are particularly affected. Patients have the presentation described in the question and typically die within several years.
    Adrenoleukodystrophy (choice A) is an X-linked disease with abnormal lipid metabolism leading to demyelination in the CNS.
    Central pontine myelinolysis (choice B) is characterized by demyelination of the pons (especially the basis pontis) seen after overlying rapid correction of hyponatremia.
    Krabbe's disease (choice C) is an autosomal recessive accumulation of cerebrosides in histiocytes in the CNS.
    Metachromatic leukodystrophy (choice E) is an autosomal recessive accumulation of sphingolipids in the CNS and elsewhere.
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    10>The correct answer is D. This couple died of carbon monoxide poisoning. Carbon monoxide has approximately 240 times the affinity for hemoglobin than does oxygen. In a sense, the hemoglobin-CO dissociation curve is shifted very far to the left compared to the hemoglobin-O2 dissociation curve. This means that the binding of hemoglobin to carbon monoxide is virtually irreversible. (The carbon monoxide that cigarette smokers inhale is cleared only when senescent red cells are phagocytized in the spleen and the hemoglobin is degraded.) In addition, the carbon monoxide shifts the hemoglobin-O2 dissociation curve to the left, making the unloading of O2 to the tissues very difficult. When too much hemoglobin is tied up with carbon monoxide, the person dies. The carbon monoxide-hemoglobin complex has a bright red color; a distinctive feature of carbon monoxide poisoning that can be helpful either at autopsy or in living patients is that this color makes the skin and organs also appear bright cherry red.
    Generally, intracellular calcium levels increase, rather than decrease (choice A), with cellular injury or death.
    Cytochrome oxidase is inhibited by cyanide (choice B).
    Ouabain is an example of a poison that inhibits Na+/K+ ATPase (choice C).
    Apoptosis (programmed cell death) is stimulated (choice E) by certain genes (e.g., p53, ced 3,4), glucocorticoids, and aging.
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    11>The correct answer is C. IgG is the predominant antibody in the secondary immune response. IgG subclass 2 is directed against polysaccharide antigens and is involved in the host defense against encapsulated bacteria.
    C3 nephritic factor (choice A) is an IgG autoantibody that binds to C3 convertase, making it resistant to inactivation. This leads to persistently low serum complement levels and is associated with Type II membranoproliferative glomerulonephritis.
    C5 (choice B) is a component of the complement system. C5a is an anaphylatoxin that effects vasodilatation in acute inflammation. It is also chemotactic for neutrophils and monocytes and increases the expression of adhesion molecules. A deficiency of C5a would affect the acute inflammatory response against any microorganism or foreign substance.
    Myeloperoxidase in phagocytic cells (choice D) is an element of the oxygen-dependent pathway present in phagocytic cells that effectively kills bacterial cells. The hydrogen peroxide-halide complex is considered the most efficient bactericidal system in neutrophils. Chronic granulomatous disease is associated with a deficiency of NADPH oxidase, which converts molecular oxygen to superoxide (the first step in the myeloperoxidase system). Patients are susceptible to granulomatous infections and staphylococcal infections.
    Secretory IgA (choice E) is the immunoglobulin associated with mucous membranes. Selective IgA deficiency is the most common hereditary immunodeficiency. In this disorder, there is failure of the B cell to switch the heavy chain class from IgM to IgA. Patients have an increased incidence of sinopulmonary infections, diarrhea, allergies, and autoimmune diseases.

    12>The correct answer is E. Sensitization to latex has become a major healthcare problem. Local skin irritations are common but more severe allergic reactions occur, up to and including rare anaphylactic reactions that are occasionally fatal. The immune responses to latex are immediate-type hypersensitivity (type I) reactions, expressing themselves in minutes, and/or delayed-type hypersensitivity (type IV) reactions, which will express themselves in 48-72 hours. The type I reactions are due to the IgE-mediated sensitivity to latex proteins while the type IV reactions are due to a cell-mediated response to the chemicals that are added in the processing of latex. The type IV response in this circumstance would be referred to as contact dermatitis.
    Irritant dermatitis (choice A) can be observed in the early stages of sensitization and can be due to sweating, rubbing, and residual soap. The timing of the reaction after 72 hours points to the type IV reaction rather than an irritant dermatitis.
    A type I reaction (choice B) would have been apparent in minutes with characteristic rhinitis, conjunctivitis, urticaria, asthma, angioedema, or anaphylaxis after she put on her latex gloves.
    A type II reaction (choice C) is a cytolytic response mediated by an antibody. The type II reaction is observed in the context of hemolytic anemias, thrombocytopenia, neutropenia, etc.
    A type III reaction (choice D) is an immune-complex response that sets into motion an inflammatory response.
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    13>The correct answer is B. The CD8+ cytotoxic T cells have antigen specific T-cell receptors (TCR) on their membranes that will recognize and bind to self class I antigens. Since the viral peptides are presented as a complex with the self class I antigens, the CD8+ cells can now recognize and react to the virus A peptides. Remember that class I antigens are expressed on all nucleated cells and platelets.
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    14>A
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    15>The correct answer is A. The clinical findings describe DiGeorge syndrome. Patients clinically present with tetany (usually first noted in the facial muscles) due to hypocalcemia secondary to hypoparathyroidism. The thymus is absent, as are the parathyroid glands, due to failure of development of the 3rd and 4th pharyngeal pouches. Recurrent infections due to defective cellular immunity and abnormal facies are additional features.
    Decreased alpha-fetoprotein (choice B) is an amniotic fluid marker for Down's syndrome. Down's syndrome patients have abnormal immune responses that predispose them to serious infections (particularly of the lungs) and to thyroid autoimmune disease. However, there is no defect of the parathyroid glands.
    Decreased IgA levels (choice C) describes selective IgA deficiency, which is the most common hereditary immunodeficiency. The syndrome is due to a failure of heavy-chain gene switching in B cells.
    Elevated IgM (choice D) is seen in hyper-IgM syndrome. Patients have a high concentration of IgM and normal numbers of T and B cells, but low levels of IgG, IgA, and IgE. Helper T cells have a defect in the surface protein CD40 ligand that interacts with CD40 on the B-cell surface. This results in an inability of the B cell to switch from the production of IgM to other classes of antibodies.
    Prominent telangiectasias around the eyes (choice E) are seen as part of the ataxia-telangiectasia syndrome. This is an autosomal recessive disorder, and is also referred to as a chromosomal breakage syndrome. Ataxia-telangiectasia is associated with increased numbers of translocations, especially involving the T-cell receptor loci; the gene for this disorder has been mapped to chromosome 11. Patients have an increased incidence of malignancy.
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    16>The correct answer is B. The patient has primary atypical pneumonia caused by Mycoplasma pneumoniae. These organisms are fastidious and difficult to culture in the laboratory, however serodiagnosis can be most helpful. Patients produce one or two heterophile antibodies during the course of the infection: one agglutinates human O+ RBCs in the cold (the cold hemagglutinins) while the other causes the agglutination of a strain of Streptococcus salivarius termed strain MG (the Strep MG agglutinins). Mycoplasma are susceptible to the macrolide family of antibiotics (erythromycin, clarithromycin, etc.). These organisms lack a cell wall, hence they are indifferent to antibiotics that interfere with peptidoglycan synthesis, such as penicillin (choice D) and ampicillin (choice A).
    Oxygen and external cooling (choice C) are therapeutic measures that are used in the treatment of severe respiratory diseases such as pneumococcal pneumonia.
    Ribavirin (choice E) is used in the treatment of respiratory syncytial virus infection in infants. This is the most common cause of hospitalization for respiratory disease in the very young, probably because aerosol administration of the antiviral compound is best accomplished in a hospital setting.
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    17>The correct answer is E. Splitting is a primitive defense mechanism in which objects or people are thought of as either "all bad" or "all good." This defense mechanism is normal in young children, but also occurs in adults with borderline personality disorder (the man in group therapy) or psychosis.
    Displacement (choice A) is an unconscious defense mechanism in which one's feelings or desires are unconsciously transferred from their original object to a more acceptable substitute.
    Fixation (choice B) refers to an arrest of development at a particular developmental stage. It is generally a partial or incomplete arrest of development, but can contribute to the development of emotional problems if protracted.
    Reaction formation (choice C) refers to an unconscious defense mechanism in which the person takes on an attitude or belief that is the opposite of his or her true beliefs and desires.
    Regression (choice D) is a return to an earlier (often infantile) stage of development that occurs in many mental illnesses and in normal individuals experiencing tragic or extremely stressful events.
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    18>The correct answer is B. All signs, including the child's report, suggest child abuse; however, there can be mitigating circumstances that are present. All states have laws requiring everyone to protect children by reporting the suspicion of child abuse to Child Protective Services. It is the responsibility of this agency to prove or disprove the suspicion, and to establish supervision of the child if abuse is verified.
    "I am going to call the police right now" (choice A), is only appropriate if the Child Protective Services is not available immediately.
    Choices C, D, and E do nothing to address the issue of the mandatory report of the suspicion of child abuse to the appropriate authorities.
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    19>The correct answer is B. The baby is exhibiting stranger anxiety, which normally occurs between the ages of 5 and 9 months.
    Let's review some other social milestones that are good to be aware of during clinical work in pediatrics:
    Spontaneous smiling begins within several days after birth and disappears by 3 months. Smiling at any face occurs by 2 months, followed quickly by smiling only at familiar faces and when pleased. By 3 months, infants can imitate facial expressions. They laugh at 4 months.
    Crying occurs from birth. It peaks at 6 weeks and is most frequent from 4-6 p.m. Colic is defined as crying more than 3 hours a day for more than 3 days a week. It often spontaneously resolves by 4 months. Treatment includes holding, avoiding overstimulation, and antispasmodics.
    Separation anxiety occurs between the ages of 10 and 18 months, when the infant is separated from the mother.
    Between the ages of 2 months and 2 years, children might show preference for a comforting "transitional object" (e.g., teddy bear), which is usually discarded by age 4, when the transition from dependence on the mother to independence is more complete.
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    20>The correct answer is E. IgG molecules contain two gamma heavy chains of a given subtype and two light chains (either kappa or lambda). The 2 in IgG2 indicates the subclass to which the molecule belongs. IgG2 contains two gamma2 chains (since a given B cell can only form one type of heavy chain). The IgG molecule will contain either two kappa chains or two lambda chains, but never one of each (choice C).
    A given cell produces immunoglobulin molecules with a single type of heavy chain (compare with choice A).
    IgG molecules with gamma1 chains (choices B, C, and D) would be of the IgG1 subclass.
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    21>The correct answer is A. The B7 molecule on the cell surface of the antigen-presenting cell reacts with the CD 28 molecule on the T cell surface for maximal costimulatory signals.
    The B7 molecule on the surface of the antigen presenting cell reacts only with CD 28 and does not react with LFA-1 (choice B) adhesion molecule.
    The ICAM- I on the surface of an antigen presenting cell reacts with the LFA- I (choice C) on the surface of a T cell for the purpose of cell-to-cell adhesion and does not function for costimulation.
    The LFA-3 (CD58) is an adhesion molecule on the surface of an antigen presenting cell. It does not react with a CD28 (choice D) costimulatory molecule on the T cell surface.
    The MHC class II molecule with its epitope does interact with a specific T cell receptor (TCR) (choice E), but this is not termed costimulatory. However, the interaction does stimulate the T cell to produce interleukins for further cell division
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    22>The correct answer is C. Yersinia enterocolitica is the pathogen producing this clinical syndrome. Yersinia is transmitted to patients via the oral route, via contaminated blood products, or by cutaneous inoculation. Patients developing iron overload because of multiple transfusions (i.e., thalassemia patients) are at increased risk of Yersinia infections because some strains are unable to synthesize bacterial iron chelators called siderophores. They can, however, use host-chelated iron stores or the drug deferoxamine (a siderophore produced by Streptomyces pilosus). Yersinia is associated with reactive arthritis following an infection by an enteropathogenic organism. Most patients who develop arthritis express HLA-B27.
    A history of asthma (choice A) is not associated with Yersinia infections.
    Deficiency in C1 esterase inhibitor activity (choice B) produces the syndrome of angioedema. This is an autosomal dominant trait associated with a deficiency of the serum inhibitor of the activated first complement component. The patients have multiple episodes of edema, affecting skin and mucosal surfaces such as the larynx and the GI tract.
    Leukopenia (choice D) is not associated with the clinical scenario in the question. Normal-to-elevated leukocyte counts are the rule in Yersinia infection.
    Serological positivity for toxoplasmosis (choice E) is not suggested because toxoplasmosis produces a different clinical picture. Toxoplasmosis can be acquired transplacentally with infected infants exhibiting a wide array of symptoms depending on when the mother was infected during gestation. Toxoplasmosis is also seen in immunocompromised patients such as those with AIDS. In this group of patients, the main organ system involved is the central nervous system.
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    23>The correct answer is E. This question illustrates an important point. An allergen or antigen must first be processed by an antigen-presenting cell in an unsensitized host before the CD 4+ T helper cells can react to it. These cells of the TH2 subclass then produce a variety of cytokines including interleukin 4. Interleukin 4 causes the heavy chain switching in the B cells from IgM to IgE. The IgE binds to the surface of mast cells or basophils by the Fc fragment. When the patient is re-exposed to the sensitizing allergen, the IgE binds to the allergen and causes degranulation of the mast cell or basophil.

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    24>The correct answer is B. Bacterial growth in a closed system is characterized by four phases:
    (1) In the initial lag phase, no growth occurs as the organisms adapt to the new environment.
    (2) In the exponential, or log phase, the organisms grow at the fastest rate and antibiotics that interfere with cell growth or division are most likely to be effective.
    (3) In the stationary phase, when nutrients have been largely exhausted, organisms tend to stop growing but may remain viable for long periods of time.
    (4) In the phase of decline, cell deaths increase due to cell starvation or exposure to toxins.

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    25>The correct answer is C. The single finding of high autoantibody titers to histones, without any other autoantibodies, is characteristic of drug-induced lupus. The most commonly implicated drugs are procainamide, hydralazine (given for hypertension), and isoniazid. Patients typically have milder disease than in SLE, and tend to have arthritis, pleuro-pericardial involvement, and, less commonly, rash. CNS and renal disease are not usually observed.
    CREST syndrome (choice A) is a milder variant of scleroderma characterized by calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly and telangiectasia. Anti-centromere antibodies are diagnostic.
    The diffuse form of scleroderma (choice B), also known as systemic sclerosis, causes fibrosis of the skin and internal viscera. This disorder is characterized by anti-SCI-70 and often low titers of many other autoantibodies.
    Sjِgren's syndrome (choice D) is characterized by dry eyes and dry mouth. Sjِgren's syndrome in isolation is characteristically positive for anti-SSA and anti-SSB. If it accompanies rheumatoid arthritis, anti-RNP will be positive as well.
    Systemic lupus erythematosus (choice E) is a multisystem disorder that is distinguished from drug-induced lupus by the presence of a wide variety of autoantibodies, including anti-double stranded DNA (anti-dsDNA).
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    26>The correct answer is D. The disease is rheumatoid arthritis, and the autoantibody is rheumatoid factor, which is usually an IgM or IgG (or less commonly IgA) directed against the constant region of autologous IgG.
    Autoantibody directed against acetylcholine receptor (choice A) is a feature of myasthenia gravis.
    Autoantibody directed against double stranded DNA (choice B) is a feature of systemic lupus erythematosus.
    Autoantibody directed against histones (choice C) is a feature of drug-induced lupus.
    Autoantibody directed against ribonucleoprotein (choice E) is a feature of mixed connective tissue disease.

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    27>The correct answer is C. The drug of choice for otitis media in children is amoxicillin. But in refractory cases, often due to bacterial resistance, switching to a different drug class is often effective. You must look for another medication that is effective against common organisms responsible for pediatric otitis media, such as Streptococcus pneumoniae (a gram-positive diplococcus) and Haemophilus influenzae (a gram-negative rod). A second-generation cephalosporin, such as cefaclor, should cover both and is the best choice. Consequently, it is commonly used in cases of amoxicillin-resistant otitis media. None of the other choices cover the proper spectrum of organisms.
    Amphotericin B (choice A) is an antifungal polyene. It works by binding to ergosterol in the fungal cell membrane, creating an artificial pore. It is used to treat systemic mycoses such as Aspergillus, Blastomyces, Candida, Coccidioides, Cryptococcus, and Histoplasma.
    Bacitracin (choice B) is a topical agent used to fight infection with gram-positive organisms. It interferes with cell wall synthesis.
    Erythromycin (choice D) is a macrolide antibiotic that binds to the 23s rRNA portion of the 50s subunit of ribosomes, inhibiting release of uncharged tRNA and stopping protein synthesis. Though effective against S. pneumoniae, it is not particularly active against H. influenzae. Note that erythromycin may be used in amoxicillin-resistant otitis media, but only when administered with a sulfonamide such as sulfisoxazole.
    Sulfamethoxazole (choice E) is a sulfonamide. It is bacteriostatic and works by inhibiting folic acid synthesis. It resembles p-aminobenzoic acid (PABA) structurally. When combined with trimethoprim (a dihydrofolate reductase inhibitor) it exerts a bactericidal effect and serves as the drug combination of choice for complicated urinary tract infections.

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    28>The correct answer is C. Neuroleptic malignant syndrome (NMS) is a potentially fatal condition that can occur at any time during the course of treatment with neuroleptics. The exact etiology is unknown. Excessive muscle contraction produces muscular rigidity, and is also responsible for the high temperature. The obtunded mental state and mutism is characteristic. Muscle relaxants, such as dantrolene, and dopamine agonists, such as bromocriptine, are used in the treatment of NMS.
    Acute dystonia (choice A, prolonged contractions of muscle groups), akathisia (choice B, "restless legs" ), and parkinsonism (choice D, pill-rolling tremor and rigidity) are all extrapyramidal side effects that occur early during neuroleptic treatment.
    Tardive dyskinesia (choice E) is a late-appearing complication of neuroleptic therapy characterized by perioral and athetoid movements.

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    29>The correct answer is E. Spore formation usually occurs during the stationary phase, when cell growth ceases because of a developing lack of nutrients or accumulation of toxins.
    During the phase of decline (choice A), the lack of nutrients and the accumulation of toxin become so severe that any viable organisms usually die before they can form spores.
    The exponential phase (choices B) and log phase (choice D) are descriptors for the steady state of active growth occurring after the lag phase and before the stationary phase. Many antibiotics are most effective in this period.
    The lag phase (choice C) is the initial period of adaptation, prior to growth, which occurs when organisms are introduced to a new environment.
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    30>The correct answer is D. This is a case of Streptococcus pneumoniae meningitis. This organism is able to attach to the respiratory mucosa because it has teichoic acids in its envelope, and because it produces an IgA protease. The IgA protease physically cleaves the immunoglobulin molecules, leaving the Fc parts to coat the bacterium. This allows the organisms to bind to the Fc receptors on various mucosal cells.
    Streptococcus pneumoniae does not produce a C carbohydrate (choice A), and thus cannot be grouped by the Lancefield terminology.
    Although the organism does produce the pneumolysin, which is an alpha-hemolytic exotoxin (choice B), this toxin mediates damage to the respiratory epithelium and inhibition of leukocytic responses, not attachment to the mucosa.
    Streptococcus pneumoniae does not produce an hyaluronic acid capsule (choice C); Streptococcus pyogenes does. Most capsules serve to inhibit phagocytosis, rather than to mediate adhesion.
    Only the group A Streptococci possess an M protein (choice E), which is used to "type" them and helps inhibit phagocytosis.
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    31>The correct answer is E. This patient has Sjِgren's syndrome, which is an autoimmune disease characterized by lymphocytic infiltration of exocrine glands resulting in dry mouth (xerostomia) and dry eyes (keratoconjunctivitis sicca). Patients have an increased risk of malignant lymphoma. Autoantibodies produced include anti-Ro (SS-A), anti-La (SS-B), antinuclear antibodies, and rheumatoid factor.
    Choice A: Anti-centromere antibodies are a very specific marker for CREST syndrome. Rheumatoid factor is usually positive in rhe

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