Endocrine Abstracts

Objective: Tumor-induced osteomalacia is a rare paraneoplastic syndrome in which fibroblast growth factor 23 (FGF-23) hyperproduction by tumor causes renal phosphate wasting, severe hypophosphatemia and osteomalacia. Localization of the tumor can be a major diagnostic challenge.

Material and methods: We present a clinical case concerning a 62-year old woman previously diagnosed with hypophosphatemic osteomalacia, with a slight improvement of clinical and laboratory manifestations after initiation of medical treatment.

Results: The patient had 10-year history of pronounced lower back pain, decrease in height by 16 cm during life, multiple atraumatic fractures of the ribs and pelvic bones. 6 years earlier she underwent surgical treatment for the mass lesion of the proximal part of the left femur (histologic examination – osteoma). She was diagnosed with hypophosphatemic osteomalacia 4 years earlier and received treatment with alfacalcidol 3 mcg/day, cholecalciferol 15 000 IU/week, calcium 1000 mg/day. The examination showed low serum P level 0.6 mmol/l (0.74–1.52), elevated PTH 111 pg/ml (15–65), normal levels of total and albumin-adjusted serum Ca, a slight increase in alkaline phosphatase (ALP) 158 IU/l (50–150) and CTx 0.836 ng/ml (0.01–0.69), 25(OH)D 23.4 ng/ml. Low tubular maximum reabsorbtion of phosphate corrected for glomerular filtration rate (TmP/GFR) 0.45 indicated renal phosphate wasting. Considering likely ectopic hyperproduction of FGF-23, we performed whole body scintigraphy with somatostatin analogue, which revealed focal intensive radiotracer uptake in left inguinal region. CT scan of the pelvic area excluded the presence of a primary focus in the area of a previously removed osteoma. After tumor-removal surgery, follow-up blood test on the 3rd day showed normalization of serum P level. Four months after surgical procedure, P level remained within the normal range, TmP/GFR showed no renal phosphate wasting. Ca level also remained within the normal range, while elevation of ALP 209 IU/l (40–150) as well as PTH 99 pg/ml (15–65) was observed, 25(OH)D 20.4 ng/ml. Marked elevation of osteocalcin 153 ng/ml (11–43) and CTx 2.34 ng/ml (0.01–0.69) suggested intense bone remodeling. Therapy with alfacalcidol, cholecalciferol and calcium was continued with increase of calcium dose up to 2000 mg/day.

Conclusion: The diagnosis of tumor-induced osteomalacia is challenging and is commonly delayed for years. Attention to biochemical values (especially serum P level) and thorough use of imaging techniques are the key steps. Only surgical removal of causative tumor can provide complete cure.