Glomus Tumor: An Unusual Cause of Hypophosphatemic Osteomalacia

Abstract

Abstract Background: Tumor-induced osteomalacia (TIO) is a rare condition resulting in hypophosphatemic osteomalacia. We present a rare case of TIO secondary to glomus tumor. Clinical Case: A 39-year-old woman with history of chronic sinusitis presented with progressively worsening generalized body pain and muscle weakness of eight months duration. Examination showed decreased muscle strength in bilateral upper and lower extremities and congenital cleft palate. Laboratory work up revealed elevated alkaline phosphatase 603 U/L (44–147 U/L), low serum phosphorus 1.5 mg/dL (3.5–5.0 mg/dL), normal serum calcium 8.9 mg/dL (8.3–10.4 mg/dL), normal 25-hydroxyvitamin D 32 ng/dL (30–100 ng/dL), elevated 1,25-dihydroxyvitamin D 62 g/mL (20–45 pg/mL), elevated intact PTH level 99.01 pg/mL (8–74 pg/mL), high normal 24 hour urinary phosphate levels 1100 mg/dl, and elevated FGF23 level 128 RU/mL (<108 RU/mL). Fractional excretion of filtered phosphate (FEPO4) [FEPO4 = (Urine phosphate / Serum phosphate) / (Urine creatinine / Serum creatinine) * 100] was 107.54 % (normal range <20%). Tubular reabsorption of phosphate (TRP) [Percentage TRP = 100 * {1- (Urine phosphate / Serum phosphate) / (Urine creatinine / Serum creatinine)}] was -7.54 %. Tubular maximum reabsorption of phosphate to glomerular filtration rate (TmP/GFR) calculated using formula [TmP/GFR = TRP x serum phosphate] was -0.1131 mg /dL (2.8–4.2 mg/dL). Bone densitometry revealed normal bone density and parathyroid scintigraphy was negative for adenoma. Clinical symptoms along with biochemical evidence of phosphate wasting confirmed by low TRP and an unsuppressed FGF23 levels suggested oncogenic osteomalacia as underlying etiology. Whole body bone scan demonstrated increased radiotracer uptake in the elbows, spine, sacroiliac joints, knees, ankles and multiple ribs suggestive of inflammatory process. MRI of paranasal sinuses revealed large soft tissue mass occupying right frontal, ethmoid, maxillary and sphenoid sinuses suggestive of sinonasal polyposis. 99mTc-Octreotide scan confirmed increased uptake in the nasopharynx. The sinonasal mass was resected and pathology revealed the mass to be a glomus tumor confirmed on immune histochemical studies with positive staining for vimentin and SMA and Ki67 of 5–10 %. Postoperatively, phosphorus levels normalized to 3 mg/dl on day 7. Conclusion: Glomus tumor as cause of TIO is extremely rare however localization and surgical resection of tumor can result in complete resolution of biochemical and clinical manifestations.