Endocrine Abstracts

A 49-year-old male with a history of hypertension, hypothyroidism, obstructive sleep apnoea, and prostatitis presented to the emergency department with a presyncopal episode and tachycardia (140 bpm). Notably, the patient’s mother had recently passed away from metastatic small bowel neuroendocrine tumour (NET). Laboratory findings revealed severe hypophosphataemia (phosphate: 0.36mmol/l, calcium: 2.41mmol/l, PTH: 8.7 pmol/l), initially managed with intravenous phosphate. Within a week of discharge, he was readmitted for recurrent hypophosphataemia and discharged on oral phosphate. His medical history included similar admissions with critically low phosphate levels (as low as 0.18mmol/l), previously attributed to diarrhoeal illness. At the endocrine clinic, further investigations showed persistently low phosphate, elevated 24-hour urinary phosphate (82mmol/day), and raised fibroblast growth factor (FGF-23) at 135 IU/ml (reference range: <100). He was prescribed alfacalcidol (0.75 mcg) and sando-phos (6 tablets daily) which stabilized his phosphate levels. Unexpectedly, gallium DOTATATE PET/CT (Ga-68 DOTATATE) imaging revealed a 15mm somatostatin receptor-expressing mesenteric nodal deposit, suggestive of a NET. No primary tumour was identified on somatostatin receptor (SSTR) imaging, contrast enhanced CT or capsule endoscopy. Following discussion at the NET MDT, the patient underwent a small bowel wedge resection and excision of mesenteric nodes, which identified a well-differentiated small bowel grade 1 NET (Ki67 <3%) staged as pT4N1R1. Postoperative phosphate levels stabilized at 0.89mmol/l, allowing him to discontinue alfacalcidol and phosphate supplementation.

Conclusion: To our knowledge, this is the first reported case of tumour-induced osteomalacia secondary to a small bowel NET. It highlights the need to consider tumour-induced osteomalacia in the differential diagnosis, the critical role of somatostatin receptor (SSTR) imaging, and multidisciplinary management in diagnosing and treating NETs with paraneoplastic manifestations.