USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

What is the MCC of autoimmune hypoparathyroidism?

1. Hypoparathyroidism

2. Hypomagnesemia

3. Primary hyperparathyroidism

4. Primary B-cell lymphoma

The correct answer is: Hypoparathyroidism

The most common cause of autoimmune hypoparathyroidism is indeed autoimmune polyglandular syndrome type 1 (APS type 1), where patients can develop autoantibodies that attack the parathyroid glands, leading to deficient parathyroid hormone (PTH) production and resultant hypoparathyroidism. This condition is often associated with other autoimmune disorders such as adrenal insufficiency and candidiasis. In the context of the other answer choices, hypomagnesemia is commonly linked to low parathyroid hormone levels, as magnesium is crucial for PTH secretion and action. However, hypomagnesemia itself is not classified as an autoimmune form of hypoparathyroidism. Primary hyperparathyroidism is typically a result of adenomas or hyperplasia of the parathyroid glands, leading to excess PTH and would not cause the deficiency seen in autoimmune hypoparathyroidism. Primary B-cell lymphoma is unrelated and would not cause hypoparathyroidism. Thus, autoimmune hypoparathyroidism stems primarily from autoimmune conditions that directly target the parathyroid glands, making it the definitive answer.