Parathyroid Disorders: Calcium Homeostasis
Disorders of the parathyroid gland are defined by abnormal secretion of Parathyroid Hormone (PTH), directly affecting serum calcium and phosphate levels.
1. Primary Hyperparathyroidism
- Etiology: Most commonly a parathyroid adenoma.
- Labs: Increased PTH, Increased Calcium, Decreased Phosphate.
- Clinical Presentation (“Bones, Stones, Groans, and Psychiatric Overtones”): Osteitis fibrosa cystica (bone pain), nephrolithiasis (kidney stones), abdominal pain (pancreatitis/ulcers), and depression/lethargy.
2. Hypoparathyroidism
| Condition | Key Mechanism |
|---|---|
| Surgical | Accidental removal of glands during thyroidectomy. |
| DiGeorge Syndrome | Developmental failure of 3rd/4th pharyngeal pouches (no parathyroids/thymus). |
| Pseudohypo | End-organ resistance to PTH; high PTH, low calcium, high phosphate. |
3. Exam Must-Knows
- Signs of Hypocalcemia: Chvostek sign (facial twitching with tapping) and Trousseau sign (carpal spasm with blood pressure cuff).
- Pseudohypoparathyroidism Type 1A: (Albright hereditary osteodystrophy) Presents with short stature, short 4th/5th digits, and cognitive impairment.
Pathology Board Hint: Always check the phosphate levels! Hyperparathyroidism lowers phosphate (via kidney excretion), whereas hypoparathyroidism raises phosphate (due to lack of excretion). If you have high PTH but LOW calcium, look for the clinical features of resistance (Pseudohypoparathyroidism).