Humoral Hypercalcaemia in Metastatic Gallbladder Cancer Presenting as Delirium: A Case Report.

Hypercalcaemia of malignancy (HCM) is a recognised paraneoplastic complication of advanced cancer, with HHM being mediated predominantly by parathyroid hormone-related protein (PTHrP) secretion. While commonly observed in squamous cell carcinomas, it is exceedingly rare in gallbladder adenocarcinoma, with only isolated case reports described in the literature. We report a man in his 50s with metastatic gallbladder cancer who presented with colicky abdominal pain, constipation, fatigue, low mood, delayed responses and insomnia. Delirium was diagnosed based on the Diagnostic and Statistical Manual of Mental Disorders- 5th Edition criteria. Laboratory evaluation revealed severe hypercalcaemia with a corrected serum calcium of 18.92 mg/dL, suppressed parathyroid hormone of 7.83 pg/mL and markedly elevated PTHrP of 701.3 pg/mL, consistent with HHM. His condition improved with intravenous hydration, bisphosphonates and calcitonin, along with multidisciplinary palliative care addressing psychological, emotional and spiritual concerns. This case highlights the need to recognise hypercalcaemia as a potential cause of delirium, even in rare malignancies, as timely diagnosis may facilitate prompt symptom management and prevent potentially life-threatening complications.