Severe Hypophosphatemia: The Hidden Truth.

Abstract

A 52-year-old woman presented with a 14-year history of progressive proximal muscle weakness and myalgia. She had been wheelchair-bound for the previous 10 years, with a significant loss of height since the onset of symptoms. She was previously healthy, with no family history of metabolic bone disease. Clinical examination revealed a proximal myopathy, short stature with marked kyphoscoliosis and pectus carinatum. Her admission laboratory investigations showed severe hypophosphatemia, with a serum phosphate of 0.87 mg/dL (0.28 mmol/L [reference interval 2.5–4.5 mg/dL; 0.8–1.4 mmol/L]). 25-Hydroxy vitamin D (25-OHD) was reduced with a normal 1,25-dihydroxy vitamin D (1,25-OHD). Laboratory results are summarized in Table 1. Of note, the tubular maximum reabsorption of phosphate for glomerular filtration rate (TmP/GFR) was 0.8 mg/dL (0.22 mmol/L [reference interval 2.0–3.4 mg/dL; 0.80–1.35 mmol/L]), suggestive of renal phosphate wasting. Fibroblast growth factor 23 (FGF-23) was elevated at 9207 pg/mL (reference interval 12–49 pg/mL). Despite phosphate and vitamin D replacement, the hypophosphatemia persisted.