Severe Symptomatic Hypercalcaemia in Recurrent Graves’ Disease: When Thyrotoxicosis Is Not the Whole Story

Hypercalcaemia is a recognised but usually mild complication of thyrotoxicosis.We describe a 66-year-old woman with recently relapsed Graves' disease who presented with profound asthenia, anorexia, marked weight loss, progressive functional decline, and an acute confusional syndrome.Investigation revealed severe hypercalcaemia with a markedly elevated parathyroid hormone (PTH) concentration and hypophosphataemia, indicating concomitant primary hyperparathyroidism (PHPT).Graves' disease was confirmed by strongly positive thyroid-stimulating hormone (TSH) receptor antibodies and compatible thyroid ultrasonography.The acute confusional syndrome was considered multifactorial, with metabolic and nutritional contributions.Hydration, electrolyte replacement, and intravenous bisphosphonate therapy progressively reduced serum calcium, with clinical improvement.Hypercalcaemia persisted during followup, and definitive surgical treatment was proposed; however, surgery had not been performed at the time of reporting.The absence of histopathological confirmation precludes differentiation between parathyroid adenoma, hyperplasia, and carcinoma and represents a limitation of this report.This case shows that hypercalcaemia in patients with thyrotoxicosis should not be automatically attributed to thyroid hormone excess.Severe or persistent hypercalcaemia requires systematic investigation, and appropriate interpretation of PTH is essential to recognise dual endocrine pathology that overlapping clinical manifestations may otherwise obscure.