Severe Hypophosphatemia and Renal Phosphate Wasting Presenting as Atraumatic Bilateral Hip Pain: Suspected Hypophosphatemic Osteomalacia.

Hypophosphatemic osteomalacia is an uncommon metabolic bone disorder that may present with nonspecific musculoskeletal symptoms, resulting in delayed diagnosis across orthopedic and emergency care pathways. We describe a 55-year-old man who presented through a National Health Service (NHS) orthopedic pathway with progressive atraumatic bilateral hip and groin pain, worsening mobility, proximal muscle weakness, and functional decline, initially managed as presumed mechanical musculoskeletal pain. Plain hip and pelvic radiographs did not identify a structural explanation for the severity of his symptoms. Initial laboratory investigations demonstrated profound hypophosphatemia (0.32 mmol/L) with markedly elevated alkaline phosphatase (428 IU/L), mildly reduced corrected calcium (2.18 mmol/L), elevated parathyroid hormone, and vitamin D insufficiency. Because the severity of hypophosphatemia appeared disproportionate to the degree of vitamin D deficiency, extended metabolic bone investigations were undertaken. Further testing demonstrated renal phosphate wasting with reduced tubular maximum phosphate reabsorption corrected for glomerular filtration rate (TmP/GFR 0.42 mmol/L) and C-terminal fibroblast growth factor 23 (FGF23) above the laboratory reference range (248 RU/mL), supporting suspected FGF23-mediated phosphate-wasting osteomalacia; localization imaging and definitive etiologic classification remained pending at the time of reporting. Severe hypophosphatemia with elevated alkaline phosphatase in patients presenting with unexplained atraumatic bilateral hip or groin pain, proximal weakness, or progressive mobility impairment should prompt consideration of metabolic bone disease and renal phosphate wasting. This case also illustrates that clinically significant osteomalacia may occur despite only mildly reduced calcium concentrations and initially nondiagnostic radiographs. Early biochemical recognition may facilitate timely specialist referral and help reduce diagnostic delay and downstream skeletal morbidity in patients with phosphate-wasting disorders.