Rare hyperparathyroidism

Rare hyperparathyroidism (Orphanet code 181408) is a broad classification encompassing uncommon forms of hyperparathyroidism — a condition in which one or more of the parathyroid glands produce excessive parathyroid hormone (PTH). This group includes various genetic and sporadic disorders that lead to abnormally elevated PTH levels, resulting in disrupted calcium and phosphorus metabolism. The parathyroid glands, located in the neck near the thyroid, normally regulate calcium homeostasis, but in these rare forms, overproduction of PTH causes hypercalcemia (elevated blood calcium), which can affect multiple organ systems including the skeletal, renal, gastrointestinal, and neurological systems. Key clinical features may include bone pain, osteoporosis, pathological fractures, kidney stones (nephrolithiasis), nephrocalcinosis, muscle weakness, fatigue, cognitive difficulties, abdominal pain, nausea, and polyuria. In severe or neonatal forms, life-threatening hypercalcemia can occur. The rare forms of hyperparathyroidism may be associated with hereditary syndromes such as multiple endocrine neoplasia (MEN types 1, 2A, and 4), hyperparathyroidism-jaw tumor syndrome (HPT-JT), familial isolated hyperparathyroidism (FIHP), or neonatal severe primary hyperparathyroidism (NSHPT). These conditions involve mutations in genes such as MEN1, RET, CDKN1B, CDC73 (HRPT2), and CASR, among others. Treatment depends on the specific underlying cause and severity. Surgical removal of the affected parathyroid gland(s) — parathyroidectomy — remains the primary curative treatment for most forms. Medical management with calcimimetics (such as cinacalcet) may be used in patients who are not surgical candidates or as a bridge to surgery. Monitoring of calcium levels, renal function, and bone density is essential. Genetic counseling is recommended for hereditary forms to identify at-risk family members and guide surveillance strategies.

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