Hyperparathyroid Crisis
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Direct answer
A serum calcium above 14 mg/dL (about 3.5 mmol/L) with vomiting, abdominal pain, dehydration, altered sensorium or arrhythmia in a patient with markedly elevated parathyroid hormone is parathyroid crisis — a rare, life-threatening end of unrecognised primary hyperparathyroidism, usually from a parathyroid adenoma and occasionally a carcinoma. Management is sequenced: aggressive isotonic saline resuscitation first (several litres in 24 hours, restoring intravascular volume and driving calciuresis), then antiresorptives — intravenous zoledronate 4 mg for durable control, calcitonin for a fast but transient effect with tachyphylaxis, denosumab when bisphosphonates are contraindicated — with dialysis against a low-calcium dialysate for renal failure. Once stabilised, localisation (sestamibi, ultrasound, 4D-CT) and parathyroidectomy in the same admission are curative; waiting weeks risks another crisis.
What you must remember
- Numbers that define the syndrome: total calcium typically above 14 mg/dL (3.5 mmol/L), PTH in the hundreds to over a thousand pg/mL, and a short QT interval with bradyarrhythmias on ECG — hypercalcaemia shortens QT, the mirror image of hypocalcaemia.
- Precipitants: dehydration, intercurrent illness, thiazides, immobilisation, contrast load; many patients have had years of mild "stones and bones" complaints before tipping.
- Saline first, drugs second: 200-500 mL/hour isotonic saline to correct volume depletion and establish a diuresis, with potassium and magnesium monitored and replaced.
- Drug layering: calcitonin acts within hours but tachyphylaxis appears within about 48 hours; zoledronate 4 mg intravenously works over 2-4 days but needs adequate renal function; denosumab is the option in renal failure.
- Dialysis: low-calcium dialysate for the oliguric or severely renally impaired patient — it removes calcium directly.
- Definitive treatment is surgical: parathyroidectomy after stabilisation cures; localisation studies precede it, and intra-operative PTH monitoring confirms adequate resection.
- Differential of severe hypercalcaemia: malignancy (PTH-related protein, osteolysis — endogenous PTH suppressed), thyrotoxicosis, immobilisation, sarcoidosis and other granulomatous disease, milk-alkali; the intact PTH assay separates parathyroid from all the rest.
- Post-operative trap: hungry bone syndrome — profound hypocalcaemia, hypophosphataemia and hypokalaemia as mineral floods into demineralised bone; monitor and replace aggressively.
Working through the crisis, step by step
Picture a 54-year-old woman brought in with five days of vomiting and confusion: calcium 16.2 mg/dL, PTH 1,240 pg/mL, creatinine 1.8. Step one is ABC with cardiac monitoring — short QT, no digoxin on board. Step two is fluids: isotonic saline at 200-300 mL/hour adjusted to her cardiac reserve, correcting the dehydration that both caused and perpetuated the crisis; you chart urine output and re-check electrolytes six-hourly. Step three layers the drugs on day one — calcitonin for immediate effect plus zoledronate for the sustained fall — and holds dialysis in reserve. Step four, as calcium drifts below 12-13 mg/dL and her sensorium clears, is localisation: sestamibi and ultrasound, with 4D-CT if discordant. Step five is parathyroidectomy during the same admission, because the only durable drop in PTH comes from removing the adenoma. The sixth step is the one trainees forget — serial calcium, phosphate and potassium for the first 72 hours post-operatively, because hungry bone syndrome can drop calcium to symptomatic levels faster than oral supplements can match.
How the exam frames it
The examiner's first trap is "treat the number, not the patient": a calcium of 12 in an asymptomatic outpatient is a different disease from 16 with vomiting and confusion, and the stem's symptoms decide urgency. The second trap is the PTH assay question — in hypercalcaemia of malignancy the intact PTH is low or normal (suppressed by the calcium), so an elevated PTH in a crisis points back to the parathyroid. The third is sequencing: bisphosphonate before fluids is wrong, and so is sending the unstable patient for a sestamibi scan. Finally, know the two ECG facts — hypercalcaemia shortens the QT interval, and a patient on digoxin becomes toxic at lower calcium levels — plus hungry bone syndrome as the post-operative plot twist.
Frequently asked questions
What calcium level defines parathyroid crisis?
A total serum calcium above 14 mg/dL (about 3.5 mmol/L) with symptoms and markedly raised PTH is the commonly quoted threshold. Symptoms, not the number alone, drive urgency.
What is the first step in management?
Aggressive isotonic saline resuscitation — typically 4-6 litres in the first 24 hours with cardiac monitoring. Volume correction precedes every drug.
Why give calcitonin and zoledronate together?
Calcitonin lowers calcium within hours but tachyphylaxis develops in about 48 hours, while zoledronate takes days to act but sustains the fall. Layering them covers the gap.
When is dialysis used?
In severe renal failure or when fluids and drugs fail, haemodialysis with a low-calcium dialysate removes calcium directly. It is a bridge to parathyroidectomy.
What is hungry bone syndrome?
Severe post-operative hypocalcaemia with hypophosphataemia as mineral deposits into long-deminerised bone. It demands close monitoring and intravenous calcium replacement.