Hypocalcemia and hypophosphatemia due to osteoblastic metastases from central nervous system embryonal tumour

A male in his early 20s presented with severe skeletal pain and diffuse osteosclerosis caused by extensive osteoblastic skeletal metastases from a Central Nervous System (CNS) Embryonal Tumour (WHO Grade 4), leading to hypocalcemia and hypophosphatemia. Biochemical evaluation revealed elevated parathyroid hormone and high vitamin D levels; imaging confirmed widespread osteoblastic metastases. Low urinary fractional excretion of calcium suggested high uptake into the bone. The biochemical profile resembled vitamin D resistance but represents a distinct pathophysiological entity. Pancytopenia due to marrow infiltration precluded chemotherapy and radiotherapy, prompting a focus on supportive and palliative care. Management included oral calcium and phosphorus supplementation alongside symptom control and psychosocial support. This case illustrates the rare metabolic complication of hypocalcemia and hypophosphatemia secondary to osteoblastic metastases in a CNS malignancy. It emphasises recognising such metabolic derangements and adopting a multidisciplinary approach to optimise management and improve patient quality of life.