A pt with muscle cramps, perioral numbness, and irritability

Discussion in 'USMLE STEP 1' started by Guest, Mar 19, 2010.

  1. Guest

    Guest Guest

    A 45-year-old male presents to the physician with muscle cramps, perioral numbness, and irritability over the past 3 to 4 months. Lab results reveal hypocalcemia, normal albumin level, and hyperphosphatemia. Parathyroid hormone level is decreased. Alkaline phosphatase level is normal. Which of the following is most likely causing this clinical scenario?

    A. Bone metastases
    B. Hashimoto's thyroiditis
    C. Hypervitaminosis D
    D. Hypomagnesemia
    E. Previous subtotal thyroidectomy
  2. Guest

    Guest Guest

    The answer is E.
    This patient is experiencing symptoms of hypocalcemia secondary to diminished parathyroid hormone (PTH) secretion. This must always be considered in a patient who undergoes total or subtotal thyroidectomy because the parathyroids are nestled in the tissue surrounding the thyroid gland.Surgical attempts to leave portions of the parathyroids intact are sometimes unsuccessful. Other causes of decreased PTH include neck irradiation, autoimmune phenomena (polyglandular autoimmune syndromes),dysembryogenesis (as in DiGeorge's syndrome), or as a result of heavy metal damage (Wilson's disease,hemosiderosis, hemochromatosis).Bone metastases (choice A) would cause hypercalcemia, as a result of osteolysis.Hashimoto's thyroiditis (choice B) is the most common cause of hypothyroidism and results in decreased thyroid hormone and elevated TSH levels. Serum calcium and PTH should be normal.Hypervitaminosis D (choice C) would cause hypercalcemia.Hypomagnesemia (choice D) may cause a functional hypoparathyroidism because magnesium is needed for PTH activity in tissue. However, in such a case, actual PTH levels would not be decreased.

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