Abstract 159: Glomus tumour presenting with oncogenic osteomalacia

Introduction: Tumour induced osteomalacia (TIO) is a rare paraneoplastic syndrome of mostly, benign mesenchymal tumours. Glomus tumours causing TIO is a very rare entity. We present a case of unresectable locally invasive glomus tympanicum with hypophosphatemic osteomalacia being misdiagnosed as bone metastases. Case Synopsis: 55 year old man presented with difficulty walking for the 2 years and wheel chair bound for 3 months. Past medical history revealed multiple surgeries for recurrent glomus tympanicum -left ear in 2011, 2013 and 2015. Tumour recurred in 2019-unresectable. Due to his bone pain, a Tc 99 MDP scan done showed increased tracer uptake in multiple ribs bilaterally and iliac bones which was interpreted as metastasis - given radiation therapy and chemotherapy. On examination- Lower limb power was 3/5 bilaterally. Other systemic examination was normal. Investigations showed S. Calcium of 8.5 mg/dl, S. phosphorus – 1.3 mg/dl with ALP- 424 IU/L, 25 (OH) D- 21 ng/ml, S. creatinine -0.9 mg/dl and iPTH-115 pg/ml. His 24 hour urine Calcium, Phosphorus and Creatinine were 107 mg, 588 mg and 1260 mg per day. Tubular reabsorption of phosphorus was 70% with TmP GFR of 1.1 suggesting renal phosphate wasting. MRI spine showed multiple vertebral compression fractures and insufficiency fractures of iliac bones suggestive of metabolic bone disease. FGF 23 was 555.6 RU/ml (0-150). Hence tumour induced osteomalacia was diagnosed. Ga DOTANOC showed only the Left glomus tumour and no other lesion. He was started on oral phosphate and Vitamin D. After 3 months his bone pains have reduced by 40-50%, he is walking independently and his S. Phosphorus levels have increased to 2.5 mg/dl.