Tubular phosphate transport: a comparison between different methods of urine sample collection in FGF23-dependent hypophosphatemic syndromes.

OBJECTIVES: Tubular maximum phosphate reabsorption per glomerular filtration rate (TmP/GFR) is used to evaluate renal phosphate reabsorption and it is a useful tool for the differential diagnosis of hypophosphatemic syndromes. TmP/GFR is typically calculated from fasting plasma and second morning void urine samples, obtained 2 h after the first void (TmP/GFR 2 h). The purpose of this study was to evaluate if TmP/GFR calculated from 24 h urine collection (TmP/GFR 24 h) can be used as an alternative for TmP/GFR 2 h in patients with urine phosphate wasting. METHODS: We enrolled adult patients with X-linked hypophosphatemia (XLH) or tumor-induced osteomalacia (TIO). All patients underwent blood and urine sample collections, to calculate TmP/GFR 24 h and TmP/GFR 2 h. RESULTS: Twenty patients (17 XLH and 3 TIO), aged 24-78 years, were included. All patients had low TmP/GFR 2 h (0.35 mmol/L, IQR 0.24-0.47 mmol/L) and TmP/GFR 24 h (0.31 mmol/L, IQR 0.22-0.43 mmol/L). The concordance correlation coefficient between TmP/GFR 2 h and TmP/GFR 24 h was 0.86 (95 % CI: 0.69-0.93), with a systematic bias of 0.05 mmol/L (95 % limits of agreement: -0.10 to 0.20). Furthermore, in 70 % (i.e., 14 patients out of 20) and 80 % (i.e., 16 patients out of 20) of cases the difference between TmP/GFR 2 h and TmP/GFR 24 h was within ±30 % and ±35 %, respectively. CONCLUSIONS: Despite TmP/GFR 2 and 24 h show a relatively suboptimal agreement, the difference between the two parameters appears to be small and not clinically significant in the setting of adult patients with FGF23-dependent urine phosphate wasting and secondary hypophosphatemia.

Hepatitis C-associated Osteosclerosis (HCAO): Long-Term Follow-Up of a New Case Recovered After Antiviral Treatment.

Hepatitis C-associated osteosclerosis (HCAO) is a very rare condition that can be observed in a small number of patients with Hepatitis C Virus (HCV) infection. HCAO is usually characterized by widespread bone sclerosis, associated with severe bone pain, and increased levels of bone turnover markers, especially alkaline phosphatase (ALP). In this report, we present the case of a 55-year-old woman who was affected by HCV and came to our attention for severe and diffuse bone pain. Radiological studies showed bone sclerosis, and bone mineral density (BMD) was markedly increased, as well as serum ALP levels. The patient was initially treated with intravenous pamidronate, which provided only a transient benefit on clinical symptoms. Then antiviral therapy for HCV (interferon-alfa and ribavirin) was started and it was effective in making the viral load undetectable. After a long follow-up period, we observed a persistent remission of bone pain, a reduction in BMD together with a progressive trend toward the normalization of bone turnover markers. In conclusion, HCAO, although rare, should be considered among the potential causes of increased bone mass in patients with HCV infection, and treatment for the underlying infection may be effective in controlling the manifestations of this disease.