PART 18 — PARATHYROID

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Study use: Rapid revision of parathyroid embryology, PTH physiology, calcium–phosphate interpretation, primary/secondary/tertiary hyperparathyroidism, hypoparathyroidism, FHH, pseudohypoparathyroidism, hungry-bone syndrome, MEN associations, parathyroid surgery, and calcium emergencies.

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Priority Guide: 🔴 Core / Must Know | 🟠 Important | 🟡 Additional

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🎯 High-Yield Overview

• 3rd pharyngeal pouch → inferior parathyroids + thymus; 4th pouch → superior parathyroids.
• PTH → serum Ca↑, renal phosphate reabsorption↓, 1α-hydroxylase↑ → calcitriol↑.
• Hypercalcemia + non-suppressed PTH → primary/tertiary HPT or FHH; hypercalcemia + suppressed PTH → PTH-independent cause.
• Primary HPT → usually single adenoma; classic labs = Ca↑ + PTH↑/inappropriately normal + phosphate↓.
• Severe HPT bone clues → subperiosteal resorption, salt-and-pepper skull, osteitis fibrosa cystica, brown tumors.
• Biochemical diagnosis precedes localization; ultrasound/sestamibi localize an abnormal gland for surgery.
• CKD secondary HPT → PTH↑ + phosphate often↑ + Ca low/normal; vitamin-D deficiency → phosphate often↓.
• Tertiary HPT → long-standing secondary disease becomes autonomous → PTH↑↑ + Ca↑.
• Hypoparathyroidism → PTH↓ + Ca↓ + phosphate↑; pseudohypoparathyroidism → PTH↑ + Ca↓ + phosphate↑.
• FHH → mild lifelong hypercalcemia + low urinary calcium; parathyroidectomy usually does not help.
• Hungry-bone syndrome after parathyroidectomy → Ca↓ + phosphate↓ from rapid skeletal remineralization.

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RED FLAGS: Severe hypercalcemia with dehydration, confusion, arrhythmia or renal dysfunction; severe hypocalcemia with tetany, seizure, laryngospasm or QT prolongation; and postoperative neck swelling with respiratory distress require urgent management.

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1. EMBRYOLOGY, ANATOMY & PTH PHYSIOLOGY

2. PRIMARY HYPERPARATHYROIDISM & BONE DISEASE

3. DIAGNOSIS, LOCALIZATION, FHH & PARATHYROID SURGERY

4. SECONDARY & TERTIARY HYPERPARATHYROIDISM