A 40-year-old patient was referred to Clinic of Endocrinology due to hypophosphatemia causing pain, cramps, and weakness of muscles. Moreover, his bone mineral density was very low. The previous treatment with phosphorus and active vitamin D metabolites was ineffective. In lab tests the hypophosphatemia, hyperphosphaturia, and elevated FGF23 levels were found. Somatostatin receptor scintigraphy (SRS) showed increased radiotracer uptake in the right maxillary sinus and CT scans confirmed presence of tumor in this localization. Biopsy and cytological examination created suspicion of mesenchymal tumor—glomangiopericytoma. Waiting for surgery the patient was treated with long acting Somatostatine analogue, and directly before operation short acting Octreotide and intravenous phosphorus were used. Histology confirmed the cytological diagnosis and the phosphatemia return to normal values in 10 days after the tumor removal. 1. Case Report A 40-year-old man was referred to Clinic of Endocrinology due to prolonged, deep hypophosphatemia causing pain, cramps, and weakness of proximal muscles. One year before, during the previous hospitalization (in neurological ward) primary muscle disease had been excluded and diagnosis of osteomalacia had been established. Diagnosis was made on basis of symptoms, low calcium and phosphorus level (2.1？mmol/L and 0.6？mmol/L, resp.), and very low 24？h calcium urine excretion (80？mg/24？h). PTH was then surprisingly normal that is, 57？pg/mL (normal ranges 15–65？pg/mL), and 25OHD3 level was undetectable (<4？ng/mL). There were no fractures in patient’s medical history; however bone mineral density was very low (in all localizations -scores and -scores <？3). Patient was treated for more than one year with calcitriol 1？μg, alfacalcidol 1？μg, calcium 1000？mg, and phosphorus 1500？mg per day. This medication had no effect on serum concentrations of phosphorus and only a moderate effect on clinical symptoms. Patient was under dental treatment (caries and periodontitis). At admission the levels of CPK, calcium, and PTH were normal; 25OHD3 level raised to 29.1？ng/dL (normal ranges 30–80？ng/dL) despite using only little amount of D3 contained in Ca/D3 preparations apart from active metabolites. Alkaline phosphatase (AP) was slightly elevated (137？U/L; normal ranges 40–129？U/L) and serum phosphorus concentration was very low (0.41？mmol/L; normal ranges 0.81–1.45？mmol/L). 24？h urine collection showed high phosphorus excretion (66.5？mmol/24？h, normal ranges 12.00–65.00？mmol/24？h). Bone mineral density was still very low: lumbar spine -score =
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