What is the most common cause of primary hyperparathyroidism?

• A. Parathyroid adenoma
• B. Parathyroid hyperplasia
• C. MEN I
• D. Secondary to CKD

Answer: (A)

Primary hyperparathyroidism occurs when one or more parathyroid glands secrete excess PTH on their own. The most common scenario is a solitary parathyroid adenoma—a benign tumor on a single gland—that autonomously produces PTH, leading to elevated calcium levels. This single-gland issue accounts for the majority of cases, making it the typical cause.

Hyperplasia of multiple glands is less common and can be seen with certain syndromes or sporadically. MEN I can involve the parathyroids but is not the predominant cause. Secondary hyperparathyroidism, such as that due to chronic kidney disease, is a different process where PTH elevation is compensatory, not driven by a primary gland tumor.