IM23.1-3 | Calcium and Parathyroid Disorders — Summary & Reflection

KEY TAKEAWAYS

Calcium homeostasis is maintained by PTH, calcitriol, and calcitonin acting on bone, kidney, and intestine. Normal serum calcium is 2.1–2.6 mmol/L; corrected for albumin as: measured Ca + 0.8 × (4 − albumin g/dL).

Classification of hypercalcaemia by PTH level:
- PTH elevated/inappropriately normal: PHPT (single adenoma 80–85%), FHH (CCR <0.01 — do NOT operate), lithium, tertiary HPT.
- PTH suppressed: malignancy (HHM from PTHrP — most common in hospitalised patients; osteolytic metastases; calcitriol-excess in lymphoma), granulomas (sarcoidosis, TB — calcitriol elevated), vitamin D toxicity, immobilisation, thyrotoxicosis.

Biochemical profile: PHPT = high Ca, high PTH, low phosphate, high urinary Ca, CCR >0.02. Malignancy-HHM = high Ca, suppressed PTH, elevated PTHrP, low phosphate.

Primary hyperparathyroidism: most are asymptomatic; symptoms include nephrolithiasis, reduced BMD, fatigue, polyuria, constipation. Diagnose by elevated Ca + elevated/inappropriately normal PTH + low phosphate. Localise with sestamibi ± ultrasound. Surgery criteria: age <50, Ca >1 mg/dL above normal, T-score < −2.5, eGFR <60, nephrolithiasis, vertebral fracture. Cinacalcet for non-surgical candidates.

Acute hypercalcaemia management: IV 0.9% saline first → IV zoledronic acid (avoid if severe renal impairment) → calcitonin as bridge → glucocorticoids for granulomatous causes → haemodialysis for refractory/severe cases. Frusemide is NOT routine — only for fluid overload.

REFLECT

Consider the opening case: a 58-year-old woman with fatigue, constipation, and 'brain fog' who was prescribed antidepressants before her calcium was checked. PHPT is one of the most commonly missed diagnoses in medicine because its symptoms are non-specific — fatigue and mild cognitive impairment are attributed to age, anxiety, or depression rather than to a biochemical cause. Reflect on what a simple calcium measurement on the first presentation might have changed for this patient. Now consider: how would you approach a patient who asks 'Do I really need surgery if I have no symptoms?' — thinking through the surgical criteria from the Fourth International Workshop guidelines, how would you explain to her why her age of 45 alone places her in the 'recommended surgery' category? Connecting the biochemical mechanism to the patient's individual risk profile is the heart of what competencies IM23.1–23.3 require of you.