Hypocalcaemic cardiomyopathy with recurrent heart failure: a natural rechallenge case report with 30-month follow-up.

Background: Hypocalcaemic cardiomyopathy is a rare but potentially reversible cause of heart failure (HF), yet it remains under-recognized in clinical practice. Evidence supporting a direct causal relationship is limited, particularly with regard to relapse and long-term follow-up. Case summary: A 71-year-old woman with post-thyroidectomy hypoparathyroidism presented with new-onset HF characterized by progressive exertional dyspnoea, orthopnoea, and paroxysmal nocturnal dyspnoea. Echocardiography revealed left ventricular and left atrial dilatation with a reduced left ventricular ejection fraction (34%) and severe functional mitral regurgitation. Electrocardiography showed sinus rhythm with prolonged corrected QT interval and T-wave inversion. Coronary angiography excluded significant coronary disease, and no alternative causes of HF were identified. Laboratory testing demonstrated severe hypocalcaemia (1.18 mmol/L) and suppressed parathyroid hormone levels. Despite guideline-directed HF therapy, symptoms failed to improve. Intravenous and oral calcium supplementation, together with calcitriol, led to rapid symptomatic and functional recovery. Two months later, discontinuation of calcium supplementation resulted in recurrent hypocalcaemia and relapse of HF, despite ongoing guideline-directed HF therapy, and again resolved after calcium repletion. During 30 months of follow-up, adherence to supplementation maintained calcium homeostasis and was associated with preserved cardiac function, with no further HF recurrence. Discussion: This case illustrates reversible and recurrent hypocalcaemic cardiomyopathy and highlights the importance of calcium homeostasis. The reproducible dechallenge-rechallenge pattern observed on two occasions provides clinically relevant evidence supporting a causal relationship between hypocalcaemia and myocardial dysfunction. Long-term biochemical monitoring and sustained adherence to calcium and vitamin D supplementation are important to prevent recurrence in patients with hypoparathyroidism.