Key Facts

Hypoparathyroidism requires active vitamin D (not standard cholecalciferol) because PTH is needed for 1α-hydroxylation. Over-treatment causes hypercalciuria and nephrocalcinosis. Post-surgical hypoparathyroidism is often transient.

Epidemiology

Relatively uncommon. Post-surgical: most common cause (~75%). Transient hypocalcaemia after thyroid/parathyroid surgery: ~10-30%; permanent: ~1-2%.

Aetiology

Post-surgical (thyroidectomy, parathyroidectomy), autoimmune (isolated or APS-1), congenital (DiGeorge/22q11 deletion), hypomagnesaemia, infiltrative, radiation, idiopathic.

Pathophysiology

PTH deficiency → reduced bone resorption → reduced calcium mobilisation; reduced renal calcium reabsorption; reduced renal phosphate excretion (→ hyperphosphataemia); reduced 1α-hydroxylation of vitamin D → reduced intestinal calcium absorption. Net result: hypocalcaemia with hyperphosphataemia. The calcium × phosphate product may be elevated → ectopic calcification risk (basal ganglia, cataracts, kidneys).

Neuromuscular (Hypocalcaemia)

• Perioral paraesthesia, digital paraesthesia (fingers, toes)
• Muscle cramps, carpopedal spasm
• Tetany
• Laryngospasm (life-threatening)
• Seizures (hypocalcaemic)

Signs

• Chvostek sign: tapping facial nerve anterior to ear → ipsilateral facial twitch (positive in ~10% of normal people)
• Trousseau sign: inflate BP cuff >SBP for 3 minutes → carpopedal spasm (main d'accoucheur) — more specific than Chvostek
• Prolonged QT interval on ECG

Chronic

• Dry skin, brittle nails, alopecia
• Dental enamel hypoplasia (if childhood onset)
• Cataracts (posterior subcapsular)
• Basal ganglia calcification (Fahr syndrome/disease if extensive)
• Cognitive impairment, depression

Red Flags

• Post-thyroidectomy: perioral tingling → check calcium urgently
• Laryngospasm → emergency
• Prolonged QT → cardiac arrhythmia risk

Biochemistry

• Serum calcium (adjusted): low (<2.1 mmol/L)
• Phosphate: high (>1.5 mmol/L)
• PTH: low or inappropriately normal
• Magnesium: check (correct if low — PTH secretion requires magnesium)
• ALP: normal or low (vs elevated in vitamin D deficiency)
• 25-OH vitamin D: check and replace if deficient
• Renal function: U&Es

Monitoring During Treatment

• 24-hour urine calcium: target <7.5 mmol/day (over-treatment → hypercalciuria → nephrocalcinosis)
• Renal USS: periodic screening for nephrocalcinosis/stones

ECG

• Prolonged QT interval (hypocalcaemia)

Other

• CT brain: basal ganglia calcification (chronic hypoparathyroidism)
• Genetic testing: if DiGeorge/APS-1 suspected

Acute Severe Hypocalcaemia (Symptomatic/Ca²⁺ <1.9 mmol/L)

• IV calcium gluconate 10%: 10mL (2.25 mmol) over 10 minutes, then infusion (40mL 10% calcium gluconate in 500mL 0.9% NaCl over 12-24 hours)
• Cardiac monitoring
• Check magnesium and replace if low (IV magnesium sulphate 8 mmol over 20 minutes)
• Start oral calcium and active vitamin D as soon as possible

Chronic Management

• Oral calcium: calcium carbonate 1-3g/day elemental calcium in divided doses (taken with meals for absorption)
• Active vitamin D: alfacalcidol 0.5-2μg OD or calcitriol 0.25-1μg BD (must use active form — PTH required for 1α-hydroxylation of standard vitamin D)
• Target: serum calcium low-normal range (2.0-2.25 mmol/L) — avoid pushing too high (hypercalciuria)
• Cholecalciferol supplementation may also be given (for general vitamin D sufficiency)

Recombinant PTH

• Natpara (rhPTH 1-84): recombinant PTH for refractory hypoparathyroidism inadequately controlled on calcium + vitamin D; reduces calcium/vitamin D supplementation needs; specialist use

Monitoring

• Serum calcium: weekly initially, then 3-6 monthly when stable
• Phosphate, renal function: regularly
• 24-hour urine calcium: 6-12 monthly (target <7.5 mmol/day)
• Renal USS: annually (nephrocalcinosis screening)

Referral Criteria

• Endocrinology: all chronic hypoparathyroidism
• Clinical genetics: DiGeorge, APS-1

Post-surgical transient: resolves in days-weeks in most. Permanent: lifelong treatment needed; good quality of life achievable with adequate replacement. Risk of long-term complications: nephrocalcinosis (~15-30%), renal impairment, basal ganglia calcification, cataracts. Over-treatment is as dangerous as under-treatment (hypercalciuria, renal stones). With optimal management, life expectancy is near-normal.

Causes of Hypocalcaemia — PTH-Based Differential

DiGeorge Syndrome (22q11 Deletion)