Discussion in 'USMLE STEP 1' started by Guest, Jun 8, 2005.

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    1>A 48-year-old white female secretary presents with progressive difficulty
    typing over the past month. She also notes that her hands begin to feel
    numb and weak after typing for long periods of time. Upon testing, which
    of the following deficits would be predicted?
    A. Difficulty in abducting the fifth finger
    B. Difficulty in adducting the thumb
    C. Difficulty in flexing digits two and three at the metacarpophalangeal joints
    D. Loss of sensation over the lateral half of the dorsum of the hand
    E. Loss of sensation over the lateral half of the palm
    F. Loss of sensation over the medial half of the dorsum of the hand
    G. Loss of sensation over the medial half of the palm

    2>The smooth part of the right atrium derives from which of the following
    embryonic structures?
    A. Bulbus cordis
    B. Primitive atrium
    C. Primitive ventricle
    D. Sinus venosus
    E. Truncus arteriosus

    3>A 66-year-old male presents with chronic fatigue. On examination, the
    patient is noted to have lymphadenopathy and an enlarged liver and spleen.
    Laboratory examination reveals a white blood cell count of 25,000/mL with
    93% lymphocytes; the lymphocytes appear small and mature. Both the
    hematocrit and platelet counts are within normal limits; however,
    hypogammaglobulinemia is also noted. Which of the following agents
    is indicated for treatment of this patient's condition?
    A. Chlorambucil
    B. Cisplatin
    C. Dacarbazine
    D. Tamoxifen
    E. Vinblastine

    4>A patient who has suffered severe chest trauma in an automobile accident
    is found to have fluid in the right pleural space. A thoracentesis reveals
    the presence of chylous fluid in the pleural space, suggesting a rupture
    of the thoracic duct. In which regions of the thorax is the thoracic
    duct found?
    A. Anterior and middle mediastinum
    B. Anterior and superior mediastinum
    C. Middle and posterior mediastinum
    D. Middle and superior mediastinum
    E. Posterior and superior mediastinum

    5>A 15-year-old boy is evaluated by a clinician for failure to develop norma
    l male secondary sexual characteristics. Physical examination reveals small
    testes, a small penis, and gynecomastia. The boy has had some difficulties
    in school, and the parents say that the school psychometrist said he had
    an IQ of 90. This patient's condition is most likely to be related to
    which of the following?
    A. Deletion
    B. Nondisjunction of an autosomal chromosome
    C. Nondisjunction of a sex chromosome
    D. Non-Robertsonian translocation
    E. Robertsonian translocation

    6>Careful testing of the visual fields in a patient complaining of difficulty
    reading demonstrates a central scotoma involving one visual field. This
    defect is most likely due to a lesion involving which of the following
    A. Macula
    B. Optic chiasm
    C. Optic radiations in the parietal lobe
    D. Optic radiations in the temporal lobe
    E. Optic tract

    7>A 70-year-old woman with a history of multiple small strokes reports to her
    physician that she has had multiple recent experiences that something or
    someone seemed very familiar, when in reality they were not familiar to
    her. This type of experience is called which of the following?
    A. Anterograde amnesia
    B. Confabulation
    C. Deja vu
    D. Jamais vu
    E. Retrograde amnesia

    8>A 33-year-old single mother of two young children visits her physician
    because of an oral ulcer. A review of systems is significant for fatigue,
    myalgia, and joint pain. Laboratory results demonstrate leukopenia, and
    a high-titered antinuclear antibody. A speckled staining pattern due
    to anti-Sm is seen with immunofluorescence; urinary protein is elevated.
    Which of the following is the most likely diagnosis?
    A. Generalized fatigue
    B. Goodpasture's syndrome
    C. Mixed connective tissue disease
    D. Scleroderma
    E. Systemic lupus erythematosus

    9>Researchers are assessing the specificity of a screening procedure for
    breast cancer in a population of 3000 women whose mothers had the disease.
    The presence or absence of a malignant condition is established by
    conventional mammography, which is assumed to be definitive for the
    purposes of comparison. The following data are collected:
    Positive Negative Total
    Cancer 90 10 100
    No cancer 360 2540 2900
    Total 450 2550 3000

    What is the specificity of the test?
    A. 90/100
    B. 90/450
    C. 2540/2550
    D. 2540/2900
    E. (90+2540)/3000

    10>A patient develops fever, shortness of breath, and appears to be quite
    ill. X-ray demonstrates bilateral interstitial lung infiltrates.
    Bronchial washings demonstrate small "hat-shape" organisms visible
    on silver stain within alveoli. Which predisposing condition is most
    likely to be present in this patient?
    A. AIDS
    B. Congestive heart failure
    C. Pulmonary embolus
    D. Rheumatoid arthritis
    E. Systemic lupus erythematosus

    11>A 35-year-old retarded man with a strong history of mental retardation
    among male relatives undergoes genetic testing. His lymphocytes are
    cultured in a medium containing methotrexate and 4% of the metaphase
    chromosomes in the lymphocytes show a breakpoint at q27.3 on the X
    chromosome. This man is at increased risk for which of the following
    cardiovascular disorders?
    A. Aortic stenosis
    B. Atrial septal defect
    C. Mitral valve prolapse
    D. Tricuspid atresia
    E. Ventricular septal defect

    12>While lying supine in bed eating, a child aspirates a peanut. Which of
    the following bronchopulmonary segments would this foreign object mos
    t likely enter?
    A. Apical segment of the left upper lobe
    B. Apical segment of the right upper lobe
    C. Medial segment of the right middle lobe
    D. Posterior basal segment of the left lower lobe
    E. Superior segment of the right lower lobe

    13>A 43-year-old man is brought to the general medicine clinic by his wife.
    She states that his memory has progressively deteriorated over the last
    several years, and that his personality has been changing. On examination,
    the physician notes abnormal, writhing movements of the man's limbs and
    hyperreactive patellar reflexes. An MRI of the head reveals a loss of
    volume in the neostriatum and cortex. A family history reveals that
    similar symptoms occurred in several members of the patient's
    family. Which of the following genetic mechanisms has been
    implicated in this disorder?
    A. Expanded trinucleotide tandem repeat
    B. Genomic imprinting
    C. Large deletion in one gene
    D. Single amino acid substitution
    E. Translocation

    14>During a routine physical examination of a 74-year-old man, a physician
    palpates a large, pulsating mass in the lower abdomen. To which of the
    following is this mass most likely etiologically related?
    A. Atherosclerosis
    B. Bacterial infection
    C. Congenital anomaly
    D. Cystic medial degeneration
    E. Syphilis

    15>The cell in the center of the electron micrograph above is important in
    wound healing and plays a role in the pathological process underlying
    Dupuytren's contracture. Which of the following cell types is
    A. Endothelial cell
    B. Myoepithelial cell
    C. Myofibroblast
    D. Pericyte
    E. Smooth muscle cell


    16>Damage to which of the following structures might produce hair cell loss?
    A. Basilar membrane
    B. Organ of Corti
    C. Reissner's membrane
    D. Scala tympani
    E. Scala vestibuli

    17>A thyroid mass usually moves with swallowing because the thyroid gland
    is enclosed by which of the following fascia?
    A. Carotid sheath
    B. Investing layer of the deep cervical fascia
    C. Pretracheal fascia
    D. Prevertebral fascia
    E. Superficial fascia


    18>The blood from an 8-year-old boy was analyzed by flow cytometry
    . The exact number of B cells was counted. Which of the following
    cell surface markers was likely used to identify the B cells in
    this blood sample?
    A. CD3
    B. CD4
    C. CD8
    D. CD19
    E. CD56

    19>A child who has had abnormal development of the membranous bones has
    a broad skull with associated facial and dental anomalies. Which
    other bones are most likely to also be affected?
    A. Clavicles
    B. Femurs
    C. Metatarsals
    D. Phalanges
    E. Tibias

    20>Which of the following drugs used in the treatment of noninsulin-dependent
    diabetes mellitus (NIDDM) has no effect on the secretion of insulin?
    A. Acetohexamide
    B. Chlorpropamide
    C. Glyburide
    D. Metformin
    E. Tolbutamide

    21>A 57-year-old man presents with a steady, severe pain in the right
    hypochondrium, nausea, vomiting, and a temperature of 102 F. He states
    that his signs and symptoms began shortly after eating his favorite
    pizza with extra cheese, pepperoni, and sausage. Laboratory examination
    reveals a white blood cell count of 13,400/mL and a serum bilirubin
    value of 2.8 mg/dL. If hepatobiliary imaging reveals an obstructed
    cystic duct, which of the following agents would be the drug of
    choice for the treatment of this patient's pain?
    A. Meperidine
    B. Morphine
    C. Naproxen
    D. Oxycodone
    E. Propoxyphene

    22>After falling on his laterally outstretched arm, a patient suffered a
    dislocation of the glenohumeral joint. Which of the following nerves
    is most likely to have been injured from this dislocation?
    A. Axillary nerve
    B. Dorsal scapular nerve
    C. Lateral pectoral nerve
    D. Medial pectoral nerve
    E. Suprascapular nerve

    23>A 45-year-old woman presents to her physician because of a severe "sore
    throat." Physical examination demonstrates fever and an extremely tender,
    enlarged thyroid gland, but no throat erythema. Serum thyroid studies
    demonstrate a mild degree of hyperthyroidism. Two months later,
    the patient is asymptomatic, and thyroid function tests have
    returned to normal. She never again experiences difficulty
    with her thyroid function. Which of the following was the most
    likely cause of her hyperthyroidism?
    A. Diffuse nontoxic goiter
    B. Graves disease
    C. Hashimoto's thyroiditis
    D. Subacute granulomatous thyroiditis
    E. Subacute lymphocytic thyroiditis

    25>A patient has an insulin-secreting tumor that is localized to the tail of
    the pancreas. Which of the following would most likely be an associated
    finding during fasting?
    A. Glycosylated hemoglobin level is increased
    B. Plasma concentration of C peptide is decreased
    C. Plasma concentration of glucagon is decreased
    D. Plasma concentration of glucose is increased
    E. Plasma concentration of proinsulin is increased

    26>A 14-year-old girl with a high fever and sore throat presents to the
    emergency room. A complete blood count with differential implies the
    presence of a viral infection. Which of the following best describe
    s the cells that indicate a viral etiology to her illness?
    A. They are basophilic with spherical dark-stained nuclei
    B. They are precursors of osteoclasts and liver Kupffer cells
    C. They contain a peripheral hyalomere and central granulomere
    D. They have azurophilic granules and multilobed nuclei
    E. They remain in the circulation approximately 120 days

    27>A 35-year-old woman notices a change in the appearance of a mole on her
    neck. Physical examination reveals that the lesion is an irregular,
    nodular, superficial mass with a variegated appearance. Biopsy
    demonstrates a primary malignant tumor. Which of the following
    factors is most predictive of the patient's long term prognosis?
    A. Circumference of lesion
    B. Darkness of lesion
    C. Degree of color variation
    D. Depth of lesion
    E. Sharpness of border between lesion and adjacent skin

    28>A patient develops a swollen and tender lymph node in his popliteal fossa.
    An infected skin lesion in which of the following sites would most likely
    induce lymphadenopathy in this region?
    A. Lateral side of the dorsum of the foot
    B. Lateral side of the thigh
    C. Medial side of the leg below the knee
    D. Medial side of the sole of the foot
    E. Medial side of the thigh


    29>A 4-year-old child living in a slum is bitten by a rat while sleeping. Two
    days later, the child develops a rash characterized by discrete
    erythematous 1-4 mm macules on the extremities and face, most obvious
    on the palms and soles. Which of the following organisms is the most
    likely cause of this child's disease?
    A. Borrelia burgdorferi
    B. Pseudomonas mallei
    C. Pseudomonas pseudomallei
    D. Spirillium minus
    E. Streptobacillus moniliformis

    30>A 25-year-old woman develops extensive pruritic wheals following
    ingestion of seafood to which she was allergic. While these lesions
    are usually not biopsied, a biopsy would probably show which of the
    following features?
    A. Dilated superficial lymphatic channels
    B. Granular complement and IgG at dermal/epidermal junction
    C. Microscopic blisters
    D. Munro microabscesses
    E. Solar elastosis

    31>A 43-year-old man presents complaining of pain in the groin. On examination,
    his physician palpates a bulge in the region of the superficial inguinal
    ring, which he diagnoses as a direct inguinal hernia. The hernial sac
    most likely
    A. is covered by all three layers of the spermatic fascia
    B. passes medial to the inferior epigastric artery
    C. passes medial to the lateral border of the rectus abdominis muscle
    D. passes posterior to the inguinal ligament
    E. passes through the deep inguinal ring
    32>A 60-year-old alcoholic smoker abruptly develops high fever, shakes,
    a severe headache, and muscle pain. He initially has a dry, insignificant
    cough, but over the next few days he develops marked shortness of breath
    requiring assisted ventilation. Chest x-ray demonstrates homogeneous
    radiographic shadowing that initially involves the left lower lobe
    but continues to spread until both lungs are extensively involved.
    Culture of bronchoalveolar lavage fluid on buffered charcoal yeast
    extract (BCYE) demonstrates a coccobacillary pathogen. Which of the
    following is the most likely causative organism?
    A. Legionella pneumophila
    B. Listeria monocytogenes
    C. Spirillium minus
    D. Staphylococcus aureus
    E. Streptococcus pneumoniae

    33>An experimental serologic test is developed to detect the presence of
    HIV antibody. Epidemiological analysis reveals the results shown
    People with HIV antibody People without HIV antibody
    Positive test 100 50
    Negative test 20 950
    What is the sensitivity of this test?
    A. 11%
    B. 67%
    C. 83%
    D. 95%
    E. 98%

    34>A 30-year-old pregnant woman of Jewish descent presents to a physician

    with painful oral ulcers. Physical examination demonstrates widespread
    erosions of her mucous membranes. Close examination reveals a friable
    mucosa, but no well-defined aphthous ulcers. Biopsy of perilesional
    mucosa demonstrates acantholysis; direct immunofluorescence
    demonstrates an intraepidermal band of IgG and C3. Which of
    the following is the most likely diagnosis?
    A. Bullous pemphigoid
    B. Dermatitis herpetiformis
    C. Herpes simplex I
    D. Herpes simplex II
    E. Pemphigus vulgaris

    35>A 40-year-old woman presents to the emergency department because of
    hematuria. Laboratory analyses show significant proteinuria, bacteria
    and white cells in the urine, and a blood urea nitrogen (BUN) of
    40 mg/dL with a creatinine of 4.0 mg/dL. Ultrasonography reveals
    enlarged kidneys, and she is given a provisional diagnosis of
    polycystic renal disease. Which of the following is likely to
    be decreased in this patient?
    A. Creatinine clearance
    B. Extracellular sodium concentration
    C. Glucose clearance
    D. Plasma creatinine levels
    E. Plasma inulin levels

    36>During development, the formation of the kidney is induced by which of
    the following structures?
    A. Allantois
    B. Mesonephric duct
    C. Mesonephros
    D. Metanephric duct
    E. Urogenital ridge

    37>A premature infant develops progressive difficulty breathing over the first
    few days of life. Deficient surfactant synthesis by which of the following
    cell types may have contributed to the baby's respiratory problems?
    A. Alveolar capillary endothelial cells
    B. Bronchial mucous cells
    C. Bronchial respiratory epithelium
    D. Type I pneumocytes
    E. Type II pneumocytes

    38>A surgeon performs an exploratory laparotomy, producing a large incision in
    the patient's abdomen. Poor blood supply to which of the following is most
    likely to cause problems during the healing process?
    A. Adipose tissue
    B. Aponeuroses
    C. Loose connective tissue
    D. Muscle
    E. Skin

    39>Which of the following would be expected to be decreased in a patient with
    chronic hypertension secondary to renal artery stenosis?
    A. Atrial natriuretic peptide levels
    B. Blood urea nitrogen (BUN) levels
    C. Glomerular filtration rate in response to captopril
    D. Net acid excretion
    E. Potassium secretion

    40>A patient, who appears to be female, is found to be 46,XY. The patient's
    vagina is very shallow, ending in a blind pouch, and there are palpable
    masses in the labia. The diagnosis of testicular feminization syndrome
    is made. Which of the following was most likely present during the early
    fetal life of this individual?
    A. A streak ovary
    B. A uterus
    C. An oviduct
    D. Depressed levels of testosterone
    E. MIF (Mullerian inhibitory factor)

    41>A healthy 42-year-old woman with a history of anxiety attacks sits in the
    hospital waiting room as her 3-year-old daughter undergoes open heart
    surgery for a septal malformation. The woman experiences a feeling of
    suffocation and is obviously hyperventilating. She informs her husband
    that she feels faint and has blurred vision. Which of the following is
    most likely to relieve the symptoms caused by hyperventilation?
    A. Breathing a 10% oxygen/90% nitrogen mixture
    B. Breathing 100% nitrogen
    C. Breathing in and out of a plastic bag
    D. Intravenous administration of bicarbonate
    E. Lying down


    42>Which of the following occurs at the darkly stained band indicated by the
    A. Acrosome reaction
    B. Aromatase acts on testosterone
    C. Capacitation
    D. Implantation receptors are exhibited
    E. Meiosis is resumed


    43>A 38-year-old AIDS patient presents to his physician's office in Kansas
    City, Missouri, complaining of fever for the past week and an increasing
    headache. He also states that sunlight hurts his eyes and that he has
    been feeling nauseated and weak. His past medical history is significant
    for Pneumocystis pneumonia and a total CD4 count of 89. Current
    medications are trimethoprim/sulfa and indinavir. Cerebrospinal
    fluid (CSF) reveals 4 WBC, and budding encapsulated yeast
    forms grow on Sabouraud's agar. Which of the following is
    an accurate description of the morphology of the infectiou
    s form of the organism responsible for the man's illness?
    A. Broad-based, budding yeasts
    B. Budding yeasts in a "pilot's wheel" arrangement
    C. Cylindrical arthroconidia
    D. Encapsulated budding yeasts
    E. Filamentous molds
    F. Septate hyphae with microconidia and macroconidia

    44>To which of the following diseases is pyruvate kinase deficiency most
    similar clinically?
    A. a-thalassemia
    B. b-thalassemia
    C. Glucose-6-phosphate dehydrogenase deficiency
    D. Hereditary spherocytosis
    E. Iron deficiency anemia

    45>A 60-year-old male with angina comes to the emergency room with severe
    chest pain unresponsive to sublingual nitroglycerin. An EKG shows ST
    segment elevation in the anterolateral leads, and thrombolytic therapy
    is initiated. If streptokinase is given to this patient, it may produce
    thrombolysis after binding to which of the following proteins?
    A. Antithrombin III
    B. Fibrin
    C. Plasminogen
    D. Protein C
    E. Thrombomodulin

    46>A child is brought to the pediatrician because of perianal itching, which
    has been disturbing the child's sleep. Physical examination reveals scaly
    skin in the perianal region. The physician instructs the parents to place
    transparent tape on the perianal region the next morning, and then retur
    n to the office. In the office, the tape is transferred to a microscope
    slide, and low-power examination of the tape reveals oval eggs that are
    flattened along one side. The microorganism most likely responsible for
    the child's symptoms is
    A. Ancylostoma duodenale
    B. Ascaris lumbricoides
    C. Enterobius vermicularis
    D. Necator americanus
    E. Trichuris trichiura

    47>A healthy, 37-year-old, recently divorced woman loses her job at the auto
    factory. She picks up her three young children from the factory day care
    center and gets into an automobile accident on the way home. Her
    5-year-old son, who was not wearing a seat belt, sustains a severe
    head injury. The woman was not hurt in the accident, but is
    hyperventilating as she sits in the waiting room at the hospital.
    She complains of feeling faint and has blurred vision. Which of
    the following is decreased in this woman?
    A. Arterial oxygen content
    B. Arterial oxygen tension (PO2)
    C. Arterial pH
    D. Cerebral blood flow
    E. Cerebrovascular resistance

    48>A 66-year-old man with urinary retention secondary to prostatic hyperplasia
    develops a spiking fever and tachypnea. Physical exam reveals intercostal
    muscle retractions and bilateral inspiratory crackles. A chest x-ray
    exhibits bilateral interstitial and alveolar infiltrates. Arterial blood
    gases demonstrate severe hypoxemia. Blood cultures would most likely
    A. gram-negative diplococci
    B. gram-negative rods
    C. gram-positive cocci
    D. gram-positive diplococci
    E. gram-positive rods

    49>A patient arrives in the emergency room after having attempted suicide by
    lacerating his wrist. No major artery was damaged, but the nerve that is
    immediately lateral to the flexor digitorum superficialis tendon is cut.
    Which of the following actions will no longer be possible?
    A. Abduction of the second digit
    B. Adduction of the second digit
    C. Adduction of the thumb
    D. Flexion at the interphalangeal joint of the thumb.
    E. Opposition of the thumb

    50>A 48-year-old female is being treated for breast carcinoma. Over the past
    few days, she has been complaining of dysuria and frequency. Laboratory
    examination revealed the presence of microscopic hematuria. The next day
    the patient developed gross hematuria. Which of the following agents
    most likely caused the development of these signs and symptoms?
    A. Cyclophosphamide
    B. Mitomycin
    C. Paclitaxel
    D. Tamoxifen
    E. Vincristine


    1>The correct answer is C. This is a classic presentation of a patient with carpal tunnel syndrome, which typically affects females between the ages of 40 and 60 who chronically perform repetitive tasks that involve movement of the structures that pass through the carpal tunnel. One important structure that passes through the carpal tunnel is the median nerve. Patients often note a tingling, a loss of sensation, or diminished sensation in the digits. There is also often a loss of coordination and strength in the thumb, because the median nerve also sends fibers to the abductor pollicis brevis, flexor pollicis brevis, and the opponens pollicis. A final function of the median nerve distal to the carpal tunnel is control of the first and second lumbricals which function to flex digits two and three at the metacarpophalangeal joints and extend interphalangeal joints of the same digits.
    Abduction of the fifth digit (choice A) is a function controlled by the ulnar nerve, which does not pass through the carpal tunnel.
    Adduction of the thumb (choice B) is a function of the adductor pollicis, which is the only short thumb muscle that is not innervated by the median nerve, but rather by the deep branch of the ulnar nerve.
    Sensation of the lateral half of the dorsum of the hand (choice D) is mediated by the radial nerve, which also does not pass through the carpal tunnel.
    Sensation over the lateral aspect of the palm (choice E) is mediated by the median nerve, however the branch innervating the palm (palmar cutaneous branch of the median nerve) passes superficial to the carpal tunnel.
    Sensation over the medial aspect of the dorsum of the hand (choice F) is mediated by the ulnar nerve.
    Sensation over the medial aspect of the palm (choice G) is mediated by the ulnar nerve.

    2> The correct answer is D. The smooth part of the right atrium (the sinus venarum) is derived from the sinus venosus. The coronary sinus and the oblique vein of the left atrium also derive from the sinus venosus.
    The bulbus cordis (choice A) gives rise to the smooth part of the right ventricle (conus arteriosus) and the smooth part of the left ventricle (aortic vestibule).
    The primitive atrium (choice B) gives rise to the trabeculated part of the right and left atria.
    The primitive ventricle (choice C) gives rise to the trabeculated part of the right and left ventricles.
    The truncus arteriosus (choice E) gives rise to the proximal part of the aorta and the proximal part of the pulmonary artery.

    3>The correct answer is A. Chronic lymphocytic leukemia (CLL) is typically a disease of the elderly, with 90% of cases occurring after the age of 50; the median age is 65. Patients will typically present with a complaint of chronic fatigue and/or lymphadenopathy. Approximately 50% of all patients with CLL present with an enlarged liver and/or spleen. CLL typically pursues an indolent course but can occasionally present as a rapidly progressive disease. The hallmark of CLL is the isolated lymphocytosis in which the white blood cell count is usually greater than 20,000/mL and between 75% and 98% of the circulating cells are small "mature" lymphocytes. Chlorambucil is classified as a nitrogen mustard, a subcategory of the alkylating agents. It is primarily used to treat chronic lymphocytic leukemia and ovarian carcinoma; it can also be used to treat Hodgkin's disease and various other lymphomas.
    Cisplatin (choice B) is an alkylating agent indicated for the treatment of metastatic testicular and ovarian tumors in combination with other agents.
    Dacarbazine (choice C) is a cytotoxic agent with alkylating properties. It is used as a single agent or in combination with other antineoplastics in the treatment of metastatic malignant melanoma, refractory Hodgkin's disease, and various sarcomas.
    Tamoxifen (choice D) is an antiestrogen hormone used in the palliative treatment of breast cancer in patients with estrogen-receptor-positive breast cancer.
    Vinblastine (choice E) is a mitotic inhibitor antineoplastic agent indicated for the treatment of Hodgkin's disease and non-Hodgkin's lymphomas, choriocarcinoma, lymphosarcoma, and neuroblastoma, as well as various other types of cancer.

    4>The correct answer is E. The mediastinum is divided into four regions. The region above the manubriosternal junction (level of fourth thoracic vertebra) is the superior mediastinum. The region below the manubriosternal junction is divided into the anterior mediastinum (anterior to the pericardium), the middle mediastinum (within the pericardium), and the posterior mediastinum (posterior to the pericardium). The thoracic duct enters the thorax through the aortic hiatus of the diaphragm. At this point it lies in the posterior mediastinum, the region posterior to the pericardium. As it ascends through the thorax and passes the level of the fourth thoracic vertebra, it enters the superior mediastinum.
    The anterior mediastinum (choices A and B) contains the thymus and fatty connective tissue.
    The middle mediastinum (choices A, C, and D) contains the heart and the roots of the great vessels.
    In addition to the thoracic duct, the superior mediastinum (choices B, D, and E) contains the ascending aorta, aortic arch, branches of the aortic arch, descending aorta, superior vena cava, brachiocephalic veins, thymus, trachea and esophagus.
    In addition to the thoracic duct, the posterior mediastinum (choices C and E) contains the descending aorta, azygos vein, hemiazygos vein and the esophagus
    5The correct answer is C. The boy probably has Klinefelter's syndrome (47, XXY), which has the typical presentation described in the question. The condition arises as a result of failure of separation (nondisjunction) of the sex chromosomes, and can be related to either paternal nondisjunction (slightly more common) or maternal nondisjunction.
    Deletions (choice A) are a common form of genetic disease and contribute to many genetic recessive diseases.
    Examples of nondisjunction of autosomes (choice B) include trisomies such as most cases of Down's syndrome (trisomy 21), Edwards' syndrome (trisomy 18), and Patau syndrome (trisomy 13).
    There are two types of translocations: non-Robertsonian (choice D) and Robertsonian (choice E). Non-Robertsonian (reciprocal) translocations result when two non-homologous chromosomes exchange genetic material. Robertsonian translocations are a special type of translocation that involve exchange of genetic material from the long arms of one acrocentric chromosome to the long arms of another acrocentric chromosome, with fusion of the centromeres. Four percent of cases of Down's syndrome are caused by this mechanism.

    6>The correct answer is A. The probable location of lesions producing visual defects is a favorite USMLE topic (and is also well worth knowing if you have occasion to work up such a patient). Here is a list that may help you sort through these problems:
    Central scotoma ~ macula
    Ipsilateral blindness ~ optic nerve
    Bitemporal hemianopia ~ optic chiasm (choice B)
    Homonymous hemianopia ~ optic tract (choice E)
    Upper homonymous quadrantanopia ~ temporal optic radiations (choice D)
    Lower homonymous quadrantanopia ~ parietal optic radiations (choice C)
    Also, cortical lesions produce defects similar to those of the optic radiations, but may spare the macula.
    --------------------------------------------------------------------------------7>The correct answer is C. This is deja vu ("seen before"), which is the experience of an event, person, or thing as familiar, even though it has never previously been experienced. Severe cases often accompany an underlying neurologic problem.
    Anterograde amnesia (choice A) is the inability to learn new facts. Most commonly, it involves both verbal and nonverbal material, but it can involve one or the other.
    In confabulation (choice B), a patient reports "memories" of events that did not take place at the time in question.
    In jamais vu (choice D), a patient fails to recognize familiar events that have been encountered before.
    In retrograde amnesia (choice E), a patient fails to remember facts or events that occurred before the onset of amnesia.
    --------------------------------------------------------------------------------8>The correct answer is E. Systemic lupus erythematosus (SLE) is a prototype connective tissue disease. The diagnosis requires four criteria to be met from a list of eleven possible criteria: malar rash, discoid rash, photosensitivity, oral ulcers, arthritis, serositis, renal disorder, neurologic disorder, hematologic disorder, immunologic disorder, and antinuclear antibody. This patient also has anti-Sm, which is pathognomonic for SLE, but is only found in 30% of the affected patients. Antinuclear antibodies (ANA) are present in 95-100% of cases of SLE; anti-double-stranded DNA is found in 70% of the cases.
    Generalized fatigue (choice A) due to being a single working mother of two children could well be a possibility, but the presence of the other criteria make SLE more likely.
    Goodpasture's syndrome (choice B) is characterized by linear disposition of immunoglobulin, and often C3, along the glomerular basement membrane (GBM). Glomerulonephritis, pulmonary hemorrhage, and occasionally idiopathic pulmonary hemosiderosis occur.
    Mixed connective tissue disease (choice C) is an overlap syndrome characterized by a combination of clinical features similar to those of SLE, scleroderma, polymyositis, and rheumatoid arthritis. These patients generally have a positive ANA in virtually 100% of the cases. High titer anti-ribonucleoprotein (RNP) antibodies may be present, generating a speckled ANA pattern. Anti-RNP is not pathognomonic for mixed connective tissue disease, since it can be found in low titers in 30% of the patients with SLE.
    Scleroderma (choice D) is characterized by thickening of the skin caused by swelling and thickening of fibrous tissue, with eventual atrophy of the epidermis. ANA are often associated with the disease, but the staining pattern is generally nucleolar.
    --------------------------------------------------------------------------------9>The correct answer is D. Specificity refers to how well a test identifies persons who do not have the disease in question. In the example, 2900 women do not have breast cancer, and 2540 of these women have a negative test. Specificity is given by (true negatives)/ (true negatives + false positives) = 2540/(2540+360) = 2540/2900.
    Choice A, 90/100, represents the sensitivity of the test; that is, the proportion of women with the condition who test positive.
    Choice B, 90/450, gives the predictive value of a positive test. Of the 450 women who tested positive, 90 actually had the condition.
    Choice C, 2540/2550, gives the predictive value of a negative test. Of the 2550 who tested negative, 2540 did not have cancer.
    Choice E, (90+2540)/3000, refers to the efficiency of a test; that is, the proportion of all subjects who were correctly classified by the test.
    --------------------------------------------------------------------------------10>The correct answer is A. The disease is Pneumocystis pneumonia, which is caused by an agent now believed to be a fungus rather than a true bacteria. Pneumocystis carinii pneumonia is seen in immunocompromised patients, particularly in those with AIDS, cancer, and in malnourished children. It can be the AIDS-defining illness.
    Congestive heart failure (choice B) predisposes the patient to pulmonary edema.
    Pulmonary embolus (choice C) can cause pulmonary infarction or sudden death.
    Rheumatoid arthritis (choice D), particularly in miners, can cause formation of lung nodules similar to subcutaneous rheumatoid nodules.
    Systemic lupus erythematosus (choice E) can cause pleuritis, but is not associated with a significantly increased incidence of pneumonia.
    --------------------------------------------------------------------------------11>The correct answer is C. The disease is Fragile X Syndrome, which is a familial form of mental retardation that is roughly as common as Down's syndrome. The phenotype has a variable expression, but can include large head circumference at birth, perinatal complications (premature birth, asphyxia, seizures), and possibly increased incidence of sudden infant death syndrome. Later, mental retardation, particularly involving language, and symptoms suggestive of attention deficit disorder and/or autism may appear. Features suggestive of connective tissue disorder (lax skin and joints, flat feet, large ears) are common. After puberty, there may be a long narrow face with prominent jaw and nasal bridge. Macro-orchidism is also common after puberty. Mitral valve prolapse and aortic root dilatation, which may appear in late adolescence or adulthood, are among the most serious complications of this disorder.
    Aortic regurgitation related to aortic root dilatation, not stenosis (choice A), can be a problem in this population.
    Common congenital cardiac malformations such as atrial septal defect (choice B) or ventricular septal defect (choice E) are not features of Fragile X syndrome, but can be seen with Down's syndrome.
    Tricuspid atresia (choice D) is a serious congenital cardiac malformation limiting flow into the right ventricle, but it is not part of Fragile X syndrome.
    --------------------------------------------------------------------------------12>The correct answer is E. Because the right main bronchus is wider and more vertical than the left, foreign objects are more likely to be aspirated into the right main bronchus. The superior segmental bronchus of the lower lobar bronchus is the only segmental bronchus that exits from the posterior wall of the lobar bronchi. Therefore, if a patient is supine at the time of aspiration, the object is most likely to enter the superior segmental bronchus of the lower lobe.
    None of the segmental bronchi of the left lung (choices A and D) are likely to receive the object because the object is less likely to enter the left main bronchus.
    The apical segment of the right upper lobe (choice B) is not likely to receive the foreign object because of the sharp angle that the upper lobar bronchus makes with the right main bronchus and the sharp angle that the apical segmental bronchus makes with the lobar bronchus.
    The medial segmental bronchus of the right middle lobe (choice C) arises from the anterior wall of the right middle lobar bronchus. Therefore, when the patient is supine, the effect of gravity will tend to prevent the object from entering this segmental bronchus.
    --------------------------------------------------------------------------------13>The correct answer is A. The disease described is Huntington's disease, which is now known to be related to an expanded trinucleotide tandem repeat on the short arm of chromosome 4. The number of trinucleotide repeats frequently increases in succeeding generations during the process of spermatogenesis.
    Prader-Willi and Angelman syndromes are frequently cited examples of genetic diseases involving genomic imprinting (choice B).
    Duchenne's muscular dystrophy is an example of a disease that is frequently due to a large deletion in a single gene (choice C).
    Single amino acid substitutions (choice D) are common in recessive diseases such as sickle cell anemia.
    Translocations (choice E) occur in disorders such as chronic myelogenous leukemia (CML; Philadelphia chromosome) and some cases of Down's syndrome.
    --------------------------------------------------------------------------------14>The correct answer is A. The mass is an abdominal aortic aneurysm, typically found in older men. Such aneurysms are almost always related to the formation of complicated atherosclerotic plaques in the aorta. Associated coronary artery disease is commonplace.
    Bacterial infection (choice B) can cause "mycotic" aneurysms; these usually involve smaller vessels.
    The small berry aneurysms that can involve the circle of Willis are congenital anomalies (choice C).
    Cystic medial degeneration (choice D) is related to the development of dissecting aneurysms (actually dissecting hematomas).
    Tertiary syphilis (choice E) typically causes aneurysms of the root and arch of the aorta, rather than the descending aorta.
    --------------------------------------------------------------------------------15>The correct answer is C. The cell is spindle-shaped like a fibroblast; however, the difference is that the cytoplasm contains several bundles of microfilaments. These bundles are parallel to the long axis of the cell and are seen immediately beneath the cell membrane and within the cytoplasm. Densities, comparable to Z-lines, can be seen along some of these bundles. The microfilaments are responsible for the contractile properties of this cell. These contractile properties, in addition to the cell's ability to link with collagen, function in wound closure in the healing process. Dupuytren's contracture, which is a contracture of the palmar fascia, is caused by interaction of these cells with collagen fibrils of the fascia.
    The endothelial cell (choice A) lines vessels. There are no vessels in the photomicrograph.
    The myoepithelial cell (choice B) contains microfilaments and is contractile. However, it is closely associated with glandular epithelium (not apparent here).
    The pericyte (choice D) is a multipotential connective tissue cell found near or around blood vessels, but it does not contain microfilament bundles such as these. There are no vessels apparent in the photomicrograph.
    The smooth muscle cell (choice E) is joined by junctions to other smooth muscle cells, arranged in bundles. Microfilaments make up most of the cytoplasm of such cells, with the nucleus in a central location.
    --------------------------------------------------------------------------------16>The correct answer is B. The structure of the cochlea is complex. The organ of Corti contains hair cells from the cochlear branch of the vestibulocochlear nerve (CN VIII). These cells rest on the basilar membrane (choice A), which separates the scala tympani (choice D) from the scala media. The hairs of the hair cells are embedded in the tectorial membrane, and movement of the basilar membrane below the cells tends to bend the hairs, which generates action potentials by the hair cells. The tectorial membrane that lies on the hair cells does not form a boundary between the different scala; the membrane separating the scala media from the scala vestibuli (choice E) is Reissner's (vestibular) membrane (choice C).
    --------------------------------------------------------------------------------17>The correct answer is C. The pretracheal layer of the cervical fascia runs from the investing layers in both sides of the lateral neck and splits to enclose the thyroid gland. Superiorly, it attaches to the laryngeal cartilages; inferiorly, it fuses with the pericardium. As a result of these connections, the thyroid gland moves with laryngeal movements.
    The carotid sheath (choice A) contains the vagus nerve, internal jugular vein, carotid artery, and lymph nodes.
    The investing layer of the deep cervical fascia (choice B) splits to enclose the trapezius and sternocleidomastoid muscles.
    The prevertebral fascia (choice D) covers muscles arising from the vertebrae.
    The superficial fascia (choice E) is immediately deep to the platysma muscle
    --------------------------------------------------------------------------------18>The correct answer is D. The best markers for identification of B cells are CD19, CD20, and CD21. The CD21 marker is a receptor for EBV (Epstein-Barr Virus).
    The CD3 marker (choice A) is present on all T cells with either a CD4 or CD8 marker. This is the marker that is used to identify total T cell count in a blood sample. The CD3 marker is used for signal transduction in the different T cells.
    The CD4 marker (choice B) is used to identify T helper cells. These are the cells that recognize exogenous peptides presented on MHC class II molecules by macrophages. CD4+ T helper cells are also involved in cell-mediated delayed hypersensitivity, production of cytokines for stimulation of antibody production by B cells, and stimulation of macrophages.
    The CD8 marker (choice C) is used to identify cytotoxic T cells. These are the cells that recognize viral epitopes attached to the MHC class I molecules of a virally infected cell.
    The CD56 marker (choice E) is used to identify NK(natural killer) cells. These cells are important in innate host defense, specializing in killing virally infected cells and tumor cells by secreting granzymes and perforins.
    --------------------------------------------------------------------------------19>The correct answer is A. In a syndrome called cleidocranial dysostosis, absence of part of the clavicles accompanies a broad skull, and facial and dental anomalies. Note that you could also have answered this question by noting that of the bones listed, only the clavicles form by intramembranous ossification.
    The femurs (choice B), metatarsals (choice C), phalanges (choice D), and tibias (choice E) are cartilaginous (formed by endochondral ossification) rather than membranous bones.
    --------------------------------------------------------------------------------20>The correct answer is D. Metformin is a drug that is often used in conjunction with oral hypoglycemic agents for the treatment of NIDDM. Its mechanism of action is two-fold: (1) it decreases the production of glucose in the liver; (2) it increases the uptake of glucose in the liver. Metformin has no effect on the secretion of pancreatic insulin.
    Acetohexamide (choice A) is an oral hypoglycemic agent that is a sulfonylurea derivative. It stimulates secretion of insulin from the pancreas.
    Chlorpropamide (choice B) is an oral hypoglycemic agent that is a sulfonylurea derivative. It stimulates secretion of insulin from the pancreas.
    Glyburide (choice C) is a sulfonylurea derivative that stimulates insulin secretion from the pancreas.
    Tolbutamide (choice E) is a sulfonylurea derivative that stimulates insulin secretion from the pancreas.
    21The correct answer is A. The patient is presenting with signs and symptoms of acute cholecystitis, which is associated with gallstones in more than 90% of all cases. This condition occurs when a stone becomes impacted in the cystic duct and inflammation develops behind the obstruction. The acute attack is often precipitated by a large fatty meal, and is characterized by the sudden appearance of severe, steady pain localized to the epigastrium or right hypochondrium. Laboratory findings often include elevated white blood cells (2,000 - 15,000/mL). Total serum bilirubin values of 1-4 mg/dL may be seen in some instances, and serum amylase may be elevated. In noncomplicated cases, treatment often includes IV alimentation, analgesics, and antibiotics, as well as withholding of oral feedings. Meperidine is the narcotic of choice since it is least likely to cause spasm of the sphincter of Oddi, probably because of its antimuscarinic properties. It is therefore preferred over morphine (choice B), oxycodone (choice D), and propoxyphene (choice E). Furthermore, propoxyphene is a narcotic agonist with mild analgesic properties; hence, it would most likely not be able to effectively treat this patient's severe pain.
    Naproxen (choice C) is a nonsteroidal anti-inflammatory drug (NSAID) indicated for the treatment of mild to moderate pain; this agent would most likely not provide sufficient pain control for this patient.
    --------------------------------------------------------------------------------22>The correct answer is A. When the head of the humerus dislocates from the glenohumeral joint, it exits inferiorly, where the joint capsule is the weakest. Immediately inferior to the glenohumeral joint, the axillary nerve exits from the axilla by passing through the quadrangular space. At this location, the downward movement of the head of the humerus can stretch the axillary nerve. The axillary nerve innervates the deltoid muscle after leaving the axilla.
    The dorsal scapular nerve (choice B) passes along the medial border of the scapula to innervate the rhomboid muscles. The nerve does not pass in the region of the glenohumeral joint.
    The lateral and medial pectoral nerves (choices C and D) branch from the lateral and medial cords of the brachial plexus, respectively, and exit through the anterior wall of the axilla to innervate the pectoralis major and minor. These nerves do not pass in the region of the glenohumeral joint.
    The suprascapular nerve (choice E) is a branch of the upper trunk of the brachial plexus and passes over the superior border of the scapula to innervate the supraspinatus and infraspinatus muscles. This nerve does not pass in the region of the glenohumeral joint.
    --------------------------------------------------------------------------------23>The correct answer is D. This patient most likely has subacute granulomatous (de Quervain's) thyroiditis, which frequently develops after a viral infection. Microscopically, it is characterized by microabscess formation within the thyroid, eventually progressing to granulomatous inflammation with multinucleated giant cells. Clinically, patients may experience fever, sudden painful enlargement of the thyroid, and/or symptoms of transient hyperthyroidism. The disease usually abates within 6 to 8 weeks.
    Diffuse nontoxic goiter (choice A) by definition does not produce hyperthyroidism.
    The hyperthyroidism of Graves disease (choice B) does not spontaneously remit.
    Hashimoto's thyroiditis (choice C) can cause transient hyperthyroidism, but then goes on to cause hypothyroidism.
    Subacute lymphocytic thyroiditis (choice E) can cause transient hyperthyroidism, but is characteristically painless.
    The correct answer is E. Hypersecretion of insulin by a pancreatic b cell tumor is a major cause of fasting hypoglycemia (plasma glucose is not increased, choice D). Symptoms are related to neuroglycopenia and could include recurrent central nervous system dysfunction during fasting or exercise. While proinsulin only makes up approximately 20% of plasma immunoreactive insulin in normal individuals, in patients with an insulinoma it contributes 30-90% of the immunoreactive insulin. Hence, plasma levels of proinsulin are increased. The increased secretion of insulin by the tumor will also lead to an increase in C peptide secretion (not decreased, choice B) since b cells secrete insulin and C peptide on a one-to-one molar ratio. Given the prolonged hypoglycemia, the amount of glycosylated hemoglobin may also be decreased, although this is not a universal finding. Certainly, an increase in glycosylated hemoglobin would not be expected (choice A). Glucagon secretion is increased by hypoglycemia and its plasma level in a patient with an insulinoma would be expected to be increased compared to normal (not decreased, choice C
    --------------------------------------------------------------------------------26>The correct answer is A. This question is really asking you two things. First, it tests whether you know that lymphocytosis is associated with viral infection. Second, it tests your knowledge of lymphocytes' histological appearance. Note that these cells are generally small and normally constitute 25%-33% of leukocytes. Two types of lymphocytes have been distinguished: T cells (involved in cell-mediated immunity) and B cells (involved in humoral immunity).
    Monocytes are precursors of osteoclasts and liver Kupffer cells (choice B) and also give rise to tissue macrophages and alveolar macrophages.
    Platelets contain a peripheral hyalomere and central granulomere (choice C).
    Neutrophils have azurophilic granules and multilobed nuclei (choice D). They increase in number in response to bacterial infection.
    Erythrocytes remain in the circulation for about 120 days (choice E).
    --------------------------------------------------------------------------------27>The correct answer is D. The lesion is a malignant melanoma. Melanomas can develop either de novo or in an existing mole. Sunlight exposure is a significant risk factor and fair-skinned persons are at increased risk of developing melanoma. The most significant factor for long term prognosis is the depth of the lesion, since the superficial dermis lies about 1 mm under the skin surface, and penetration to this depth is associated with a much higher incidence of metastasis than is seen with a more superficial location.
    The circumference of the lesion (choice A) is much less important than depth, since one form of melanoma (superficial spreading) can still have good prognosis despite large size, if it has not extended to the depth of the superficial dermal lymphatic bed.
    The darkness (choice B) or degree of variation in color (choice C) do not have prognostic significance once melanoma is diagnosed.
    Irregularity, or fuzziness at the border (choice E) of a mole-like lesion is a good clue to potential malignancy, but does not affect prognosis once a melanoma is diagnosed.
    --------------------------------------------------------------------------------28>The correct answer is A. Most of the venous drainage of the skin of the lower extremity is to the long saphenous vein, the accompanying lymphatics of which drain into the superficial group of the inguinal lymph nodes. However, the skin drained by the short saphenous vein, including that of the lateral aspect of the dorsum of the foot, is an exception to this rule. Lymphatic fluid from this area drains into lymphatics accompanying the short saphenous vein, then drains into lymph nodes behind the knee in the popliteal fossa.
    The lateral side of the thigh (choice B), the medial side of the leg below the knee (choice C), the medial side of the sole of the foot (choice D), and the medial side of the thigh (choice E) all drain to the superficial inguinal nodes.
    --------------------------------------------------------------------------------29>The correct answer is E. The child has "rat-bite fever." This occurs in two forms with somewhat similar clinical manifestations. The form this child has is the Haverhill fever form, caused by Streptobacillus moniliformis and characterized by a short (often 1-3 days) incubation period. The Haverhill form is more common in the United States than the Sodoku form, which is caused by Spirillium minus, has a 1-4 week incubation period, and is most prevalent in Japan. One of the problems with diagnosing these diseases is that the victims are usually young children, and the bite site may be inapparent by the time the disease becomes severe enough for the child to be taken to a doctor.
    Borrelia burgdorferi (choice A) causes Lyme disease, which is characterized by an expanding erythematous rash, arthralgias, and eventual nervous system involvement.
    Pseudomonas mallei (choice B) causes glanders, which generally affects horses or humans in close contact with equines.
    Pseudomonas pseudomallei (choice C) causes melioidosis, a rare pulmonary disease found mostly in Southeast Asia.
    Spirillium minus (choice D) causes the Sodoku form of rat-bite fever.
    --------------------------------------------------------------------------------30>The correct answer is A. Urticaria (hives) are pruritic wheals that form after mast cells degranulate and trigger localized dermal edema with dilated superficial lymphatic channels. The mast cell degranulation is sometimes, but not always, triggered by IgE-antigen interactions.
    Granular complement and IgG deposition at the dermal/epidermal junction (choice B) is a characteristic of systemic lupus erythematosus.
    Microscopic blisters (choice C) are a characteristic of dermatitis herpetiformis.
    Munro abscesses (choice D) are a characteristic of psoriasis.
    Solar elastosis (choice E) is found in actinic keratoses.
    --------------------------------------------------------------------------------31>The correct answer is B. Direct inguinal hernias enter the inguinal canal by tearing through the posterior wall of that structure. The typical location for this type of hernia is through the inguinal triangle, bounded laterally by the inferior epigastric artery, medially by the lateral border of the rectus abdominis, and inferiorly by the inguinal ligament. Direct inguinal hernias pass medial to the inferior epigastric artery, whereas indirect inguinal hernias pass lateral to the inferior epigastric artery because the deep inguinal ring is lateral to the artery.
    Indirect inguinal hernias are covered by all three layers of the spermatic fascia (choice A). Direct inguinal hernias are covered by fewer than all three layers because the direct inguinal hernia tears through one or more layers of fascia as it emerges though the abdominal wall.
    The lateral border of the rectus abdominis muscle (choice C) forms the medial border of the inguinal triangle. All inguinal hernias pass lateral to the rectus abdominis.
    Femoral hernias pass posterior to the inguinal ligament (choice D). Inguinal hernias emerge through the superficial inguinal ring, which is superior to the inguinal ligament. Inguinal hernias that descend below the inguinal ligament pass anterior to the ligament.
    Indirect inguinal hernias pass through the deep inguinal ring (choice E); direct inguinal hernias do not. Both types of inguinal hernias pass through the superficial inguinal ring.
    32>The correct answer is A. The patient has a severe, potentially fatal, pneumonia with prominent systemic symptoms. Culture on BCYE is the specific clue that the organism is Legionella pneumophila. The disease is respiratory Legionellosis, also known as Legionnaire's disease, because the disease was first described when it occurred in epidemic form following an American Legion convention at a Philadelphia hotel. Patients tend to be older (40-70 years old) and may have risk factors including cigarette use, alcoholism, diabetes, chronic illness, or immunosuppressive therapy.
    Listeria monocytogenes (choice B) causes listeriosis and is not a notable cause of pneumonia.
    Spirillium minus (choice C) is a cause of rat-bite fever and is not a notable cause of pneumonia.
    Staphylococcus aureus (choice D) can cause pneumonia, but is easily cultured on routine media.
    Streptococcus pneumoniae (choice E) can cause pneumonia, but is easily cultured on routine media.

    --------------------------------------------------------------------------------33The correct answer is C. Sensitivity is defined as the ability of a test to detect the presence of a disease in those who truly have the disease. It is calculated as the number of people with a disease who test positive (true positive) divided by the total number of people who have the disease (true positive + false negative). In this case, sensitivity equals the number of people with HIV antibody who test positive (100) divided by the total number of people who have HIV antibody (120). This yields 100/120 = 83% (not a very sensitive test).
    11% (choice A) corresponds to the prevalence of the disease in the tested population, which in this case equals the total number of people with HIV antibody (true positive + false negative = 100 + 20 = 120) divided by the total number of people tested (100 + 20 + 50 + 950 = 1120). This yields 120/1120 = 11%.
    67% (choice B) corresponds to the positive predictive value of the test, which equals the number of people with the disease who test positive (true positives = 100) divided by the total number of people testing positive (all positives = 50). This yields 100/150 = 67%.
    95% (choice D) corresponds to the specificity of the test, which equals the number of people without HIV antibody who test negative (950) divided by the total number of people without HIV antibody (10
  2. DrArnab

    DrArnab Guest

    are these real USMLE questions?
  3. Guest

    Guest Guest

    plz where are the ans for 34-50?

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