Related Subjects:
|PTH Physiology
|Calcium Physiology
|Magnesium Physiology
|Calcitonin
|Hypocalcaemia
|Hypercalcaemia
|Hypomagnesaemia
|Hypermagnesaemia
|Primary Hyperparathyroidism
|Familial hypocalciuric hypercalcaemia (FHH)
|Sarcoidosis
🧪 Secondary Hyperparathyroidism is driven by low calcium, high phosphate, and vitamin D deficiency – often due to chronic kidney disease (CKD). This triggers a compensatory rise in PTH, which can eventually become autonomous (progressing to tertiary hyperparathyroidism).
📖 About
- Defined as a compensatory increase in PTH secretion in response to chronic hypocalcaemia and hyperphosphataemia.
- Most commonly associated with CKD, but also occurs in vitamin D deficiency and malabsorption syndromes.
- Chronic stimulation of parathyroid glands may cause nodular hyperplasia and, over time, autonomous function ➝ tertiary hyperparathyroidism.
🔎 Causes
- 🍳 Low Vitamin D intake/deficiency ➝ impaired calcium absorption.
- 💧 Chronic Kidney Disease ➝ reduced calcium reabsorption, phosphate retention, ↓ 1α-hydroxylase activity ➝ ↓ calcitriol (active vitamin D).
- Malabsorption syndromes (e.g. coeliac disease, IBD).
⚙️ Aetiology & Pathophysiology
- CKD is the primary driver of SHPT due to reduced excretion of phosphate and impaired vitamin D metabolism.
- Resulting hypocalcaemia stimulates parathyroid glands to increase PTH secretion 🦴.
- With persistent stimulation, parathyroid glands undergo hyperplasia and may lose feedback control ➝ tertiary hyperparathyroidism.
🩺 Clinical Features
- Often subtle, dominated by features of underlying CKD.
- Renal osteodystrophy ➝ bone pain, fractures, skeletal deformities.
- Vascular & soft tissue calcification ➝ increased cardiovascular morbidity and mortality 💔.
- Pruritus, muscle weakness, and extraskeletal calcification may develop.
🔬 Investigations
- 🧪 Biochemistry:
- ↑ Urea & Creatinine (reduced eGFR, CKD).
- ↓ or normal calcium.
- ↑ Phosphate (due to retention).
- ↓ 1,25(OH)₂ Vitamin D.
- ↑ ALP (due to increased bone turnover).
- ↑ PTH (appropriate compensatory rise).
- 🦴 X-rays: subperiosteal erosions, osteitis fibrosa cystica, osteomalacia.
- Bone density scans may reveal osteopenia/osteoporosis.
💊 Management
- 🍽️ Diet: Low-phosphate diet + phosphate binders (e.g. calcium carbonate, sevelamer).
- ☀️ Vitamin D analogues: Alfacalcidol or calcitriol to suppress PTH and correct hypocalcaemia.
- 🧪 Cinacalcet: Calcimimetic agent used if PTH remains >85 pmol/L despite other measures.
- 🔪 Parathyroidectomy: For refractory cases or severe bone disease.
- Optimisation of CKD management (dialysis, transplant consideration).
📚 References
