Makindo Medical Notes

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

• Secondary Hyperparathyroidism: Pathogenesis, Disease Progression, and Therapeutic Options