Makindo Medical Notes

Related Subjects: |PTH Physiology |Calcium Physiology |Magnesium Physiology |Calcitonin |Hypocalcaemia |Hypercalcaemia |Hypomagnesaemia |Hypermagnesaemia |Primary Hyperparathyroidism |Familial hypocalciuric hypercalcaemia (FHH) |Sarcoidosis

Hypoparathyroidism most commonly results from anterior neck surgery (≈75% of cases). The condition leads to low PTH, hypocalcaemia, and hyperphosphataemia, with potentially life-threatening neuromuscular and systemic complications.

📖 About

• Rare endocrine disorder caused by inadequate secretion of parathyroid hormone (PTH).
• Classically presents with features of hypocalcaemia.
• See also: linked articles on calcium physiology & hypocalcaemia management.

🧾 Aetiology

• Primary: Autoimmune destruction, genetic syndromes (e.g. DiGeorge, Bartter’s), idiopathic.
• Secondary: Anterior neck surgery (thyroidectomy, parathyroidectomy), radiation injury, hypomagnesaemia (inhibits PTH secretion).
• Biochemistry: Low PTH, low calcium, high phosphate, normal ALP.

🧬 Definition (per guidelines)

• Albumin-adjusted hypocalcaemia confirmed on ≥2 occasions, ≥2 weeks apart.
• PTH undetectable or inappropriately low (<20 pg/mL) in the presence of hypocalcaemia.
• Phosphate usually high or upper-normal.
• After neck surgery, chronic hypoparathyroidism is defined after 6 months.

🩺 Clinical Features

• Neuromuscular irritability: tingling, cramps, carpopedal spasm, seizures, stridor.
• Chronic complications: basal ganglia calcification, nephrocalcinosis, ectopic calcium deposits (joints, eyes, skin, vasculature).
• Long-standing disease can lead to impaired renal and skeletal health.

🔍 Investigations

• Bloods: Ca²⁺ low, Phosphate high, PTH low, Mg²⁺ (exclude deficiency), U&E, vitamin D metabolites.
• ECG: Prolonged QTc interval.
• Urine: 24-hr calcium, creatinine clearance, stone risk profile.
• Imaging: Renal US/CT (nephrocalcinosis), skull X-ray (calcifications).
• BMD: DXA scan to assess bone mineral density.

💊 Management

• Correct Mg²⁺ first if deficient.
• Activated vitamin D analogues (e.g. Calcitriol 1,25(OH)₂D) ± oral calcium supplements.
• Thiazide diuretics with low salt diet → reduce urinary calcium loss.
• Phosphate binders + low phosphate diet if hyperphosphataemia persists.
• PTH replacement therapy (recombinant PTH) – emerging option in refractory/chronic cases.
• Regular monitoring for renal function, nephrocalcinosis, and calcium/phosphate balance.

📚 References

• Management of Hypoparathyroidism: Guidelines
• Review of Hypoparathyroidism (NCBI)

Cases — Primary & Secondary Hypoparathyroidism

• Case 1 — Post-Thyroidectomy Hypocalcaemia ⚠️ (Primary): A 52-year-old woman undergoes total thyroidectomy for multinodular goitre. On day 2 post-op, she develops perioral tingling, hand cramps, and a positive Trousseau’s sign. Bloods: Ca²⁺ 1.75 mmol/L (low), PO₄³⁻ high, PTH low. Diagnosis: Primary hypoparathyroidism due to surgical damage to parathyroid glands. Management: IV calcium gluconate acutely; long-term oral calcium + alfacalcidol/calcitriol.
• Case 2 — Autoimmune Hypoparathyroidism 🧬 (Primary): A 30-year-old woman with Addison’s disease presents with muscle cramps, cataracts, and seizures. Bloods: low Ca²⁺, high phosphate, low PTH. Diagnosis: Autoimmune primary hypoparathyroidism (part of polyglandular autoimmune syndrome). Management: Calcium + active vitamin D analogues; monitor renal function and Ca²⁺ levels closely.
• Case 3 — CKD-Related Secondary Hypoparathyroidism 💧 (Secondary): A 65-year-old man with CKD stage 5 (on haemodialysis) develops bone pain and pruritus. Bloods: Ca²⁺ low–normal, phosphate high, PTH elevated. Diagnosis: Secondary hyperparathyroidism due to CKD, causing hypocalcaemia. Management: Phosphate binders, vitamin D analogues (alfacalcidol), optimise dialysis, consider calcimimetics.
• Case 4 — Vitamin D Deficiency 🌥️ (Secondary): A 45-year-old man with coeliac disease and poor sunlight exposure presents with diffuse bone pain and proximal muscle weakness. Bloods: Ca²⁺ low, phosphate low, PTH elevated, Vit D low. Diagnosis: Secondary hypoparathyroidism due to vitamin D deficiency. Management: Oral vitamin D supplementation, calcium replacement, treat underlying malabsorption.

Teaching Commentary 🧠

- Primary hypoparathyroidism = low PTH → low Ca²⁺, high phosphate (classically after thyroid surgery or autoimmune). - Secondary hypoparathyroidism = compensatory ↑PTH due to chronic hypocalcaemia (from CKD, Vit D deficiency, malabsorption). - Symptoms: paraesthesia, tetany, seizures, psychiatric changes, prolonged QT. - Management always targets the cause: replace calcium & vitamin D in primary; treat CKD or Vit D deficiency in secondary. ⚠️ Key distinction = **PTH levels** (low in primary, high in secondary).