Electrolyte Disorders (Calcium, Magnesium, Phosphate) — DCE Clinical Case

Calcium-focused history — what you must establish

• The symptom pattern: perioral and digital paraesthesia, cramps, carpopedal spasm episodes, and red-flag neurological symptoms — stridor, seizures, syncope or palpitations (long QT) — plus their temporal relationship to the surgery [2].
• The surgical and endocrine context: indication for thyroidectomy, final histology (any parathyroid tissue in the specimen), voice change since surgery (recurrent laryngeal nerve), and whether calcium and PTH were ever checked post-operatively [2].
• The modifiers: current calcium/vitamin D therapy and adherence, PPI or diuretic use, alcohol, bowel symptoms suggesting malabsorption, menstrual and fracture history (chronic hypocalcaemia and vitamin D deficiency both speak to bone) [4] [5].
• The impact: work, driving (seizure and arrhythmia safety), mood and cognition — the quality-of-life burden of hypoparathyroidism is part of the assessment, not a soft extra [3].

Systematic examination routine

1. General inspection first: is there carpopedal spasm at rest? Look at the neck for the thyroidectomy scar; inspect for cataracts (chronic hypocalcaemia) and any band keratopathy at the limbus; note habitus — short stature, round facies and brachydactyly would redirect you toward a GNAS imprinting disorder rather than surgical hypoparathyroidism [2].
2. Chvostek sign: tap the facial nerve just anterior to the tragus, over the parotid, and watch for ipsilateral twitching at the mouth or eye. Perform it gently on both sides [1].
3. Trousseau sign: inflate the sphygmomanometer cuff above systolic pressure for up to 3 minutes and watch the hand — carpopedal spasm is thumb adduction with metacarpophalangeal flexion and interphalangeal extension (the main d'accoucheur hand). Release promptly once positive; it is uncomfortable [2].
4. State the sensitivity honestly, aloud: Hoffman's clinical study found Chvostek positive in a substantial minority of people with normal calcium, and both signs can be absent in chronic, adapted hypocalcaemia — the signs support the diagnosis, they never exclude it [1].
5. Complete the circuit: brief neuromuscular screen (proximal myopathy of osteomalacia), an offer of ECG for QT prolongation, and the blood set: corrected calcium, phosphate, magnesium, PTH, 25-OH vitamin D and renal function [2] [5].

Presentation template (deliver this to the examiner)

"This 52-year-old woman, two years post-total-thyroidectomy, describes perioral paraesthesia and cramps. She has no carpopedal spasm at rest. Chvostek sign is positive on the right and Trousseau sign is positive at 90 seconds of cuff inflation — findings consistent with latent hypocalcaemia, most likely post-surgical hypoparathyroidism, acknowledging these signs support but do not exclude the diagnosis. She has a low surgical scar with a normal voice, no cataracts, and no features of Albright hereditary osteodystrophy. I would confirm with corrected calcium, phosphate, magnesium, PTH and vitamin D, check an ECG for QT prolongation, and — if confirmed — treat with oral calcium plus calcitriol targeting the low-normal range with a normal urine calcium, while checking her magnesium" [1] [2] [3].

Discussion questions

"Both your signs were negative. Does that exclude hypocalcaemia?" — "No. Chronic hypocalcaemia adapts, and latent tetany signs are insensitive — Hoffman found Chvostek positive in some normocalcaemic people and absent in a proportion of genuinely hypocalcaemic patients. The biochemistry decides; the signs only shift probability" [1].

"Her calcium is 1.92 with a PTH of 1.8 pmol/L (low). What is your interpretation?" — "Inappropriately low PTH with hypocalcaemia is parathyroid failure — in her case almost certainly surgical. The two things I check before settling are magnesium, because severe hypomagnesaemia suppresses PTH secretion and action and reverses with replacement, and the phosphate, which should be relatively high in hypoparathyroidism and low in vitamin D deficiency where the PTH would be appropriately high" [2] [4] [5].

"Why calcitriol rather than ordinary vitamin D?" — "PTH drives renal 1-alpha-hydroxylation. Without PTH she cannot efficiently activate cholecalciferol, so the backbone of chronic therapy is oral calcium plus calcitriol or alfacalcidol. The target is symptom relief at a low-normal calcium with a normal urine calcium — she has lost the PTH brake on renal calcium excretion, so overtreatment buys nephrocalcinosis, and chronic monitoring includes urine calcium and periodic renal imaging" [2] [3].

"She calls you tonight with worsening cramps and a tight feeling in her throat. What do you do?" — "That is possible laryngospasm — she comes in now. Symptomatic acute hypocalcaemia gets IV calcium gluconate 10% 10–20 mL slowly over 10–20 minutes with ECG monitoring, never pushed, followed by a titrated infusion, magnesium correction, and then consolidation onto oral calcium and calcitriol before discharge" [2] [3].