Parathyroid Disorders govern calcium and phosphate homeostasis through PTH. Hyperparathyroidism (excess PTH) produces hypercalcemia — the classic board mnemonic is "bones, stones, groans, and psychic moans": bone pain/pathologic fractures, renal stones/polyuria, GI upset (nausea, constipation, anorexia), neuropsychiatric symptoms (depression, confusion, fatigue). Primary hyperparathyroidism: parathyroid adenoma. Treatment: surgical parathyroidectomy. Hypoparathyroidism (PTH deficit) — most commonly from incidental parathyroid removal during thyroidectomy — produces hypocalcemia: tetany, Trousseau sign (carpal spasm with BP cuff inflated above systolic for 3 minutes), Chvostek sign (facial twitch when tapping anterior to the ear over CN VII), laryngospasm, prolonged QT interval, and seizures. Boards test post-thyroidectomy monitoring: calcium check within 24–48 hours, calcium gluconate at bedside, Trousseau and Chvostek assessment, and safe IV calcium administration (slow drip — IV push calcium causes fatal cardiac dysrhythmia).