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

What characterizes the MCC of hypoparathyroidism?

1. Thyroid surgery

2. Autoimmune cause

3. Increased serum phosphorus

4. Calcification of basal ganglia

The correct answer is: Autoimmune cause

The most common cause of hypoparathyroidism is indeed related to thyroid surgery. When the thyroid gland is surgically removed or inadvertently damaged during thyroid surgery, the parathyroid glands can also be affected, leading to decreased levels of parathyroid hormone (PTH) and resulting in hypoparathyroidism. This typically manifests as low serum calcium and potentially increased serum phosphorus due to reduced PTH activity, which helps regulate calcium and phosphorus levels in the body. In the context of hypoparathyroidism, autoimmune causes can lead to varying hormonal deficits but are not the predominant or most common cause compared to surgical intervention. Additional characteristics of hypoparathyroidism can include signs of hypocalcemia, such as tetany, seizures, and neuromuscular excitability, along with potential calcification in the brain, like calcification of the basal ganglia, but these are more complications and do not represent a primary cause. Thus, acknowledging the implications of these conditions helps clarify why surgical intervention is the most common source of hypoparathyroidism, as it is directly associated with a loss of functional parathyroid tissue.