USMLE Step 1 Question 375

Question:

A 26 year old female presents to the physician after falling and injuring her hand in a squash game. An x-ray of the patient’s hand is shown. The physician notes that the patient is of short stature and obese. In addition, the physician is able to elicit twitching of the facial muscles after tapping the patient’s cheek right in front of her ear. The physician suspects an underlying genetic condition. Which of the following laboratory abnormalities is this patient likely to have as a result of the genetic condition?

Correct Answer: D.  Hypocalcemia

This patient likely has pseudohypoparathyroidism, an autosomal dominant genetic disorder in which the kidneys are unresponsive to parathyroid hormone, leading to hypocalcemia, and hyperphosphatemia.
The cluster of obesity, short stature, shortened 4th and 5th metacarpals and hypocalcemia is characteristic of pseudohypoparathyroidism. The physician was able to elicit a Chvostek sign (twitching of facial muscles after tapping the facial nerve just in front of the ear) which is a sign of hypocalcemia. (Choice D) Excess growth hormone (Choice A) is likely to be seen in acromegaly, a condition in which the pituitary gland secretes excess growth hormone and causes the liver to produce more IGF. Patients usually present with large hands, feet, increased jaw size and frontal bossing (increased forehead prominence).

Hypercortisolism (Choice B) would be seen in Cushing’s syndrome, which could be due to a pituitary adenoma secreting excess ACTH or to primary adrenal hyperplasia, both possibly associated with MEN syndromes. Cushing’s is associated with osteoporosis, but characteristic physical findings include truncal obesity, moon facies and purple skin striae, none of which are mentioned in the question.

Hypoaldosteronism (choice C) would be seen in Addison’s disease, or primary hypoaldosteronsm (Conn Syndrome), in which the adrenal glands are unable to secrete aldosterone. There is an association with skin hyperpigmentation due to Melanocyte Stimulating Hormone.

Hypophosphatemia (choice E) is likely to be seen in hyperparathyroidism, in which the excess parathyroid hormone causes phosphate to be spilled into the urine. Hyperparathyroidism is usually due to a parathyroid adenoma, which could be due to genetic conditions such as MEN I (Multiple Endocrine Neoplasia).