Discussion

A 22-year-old female presented to the emergency room with intractable bilateral lower extremity pain of 3 months duration, starting 1 month after an uncomplicated Cesarean section. The pain was aching in character, and described as “emanating from [her] bones. ” She reported similar daily pain lasting anywhere from 4 to 8 hours when she was a child, starting at age 5, eventually resolving by age 14, and during each of her other 2 successful pregnancies. Family history was significant for the patient’s brother having similar lower extremity pain when he was a child. Physical examination revealed significant tenderness over the bony prominences of her lower extremities and the inability to ambulate. Otherwise sensation was intact, and peripheral pulses were 2+ bilaterally. A triple phase bone scan was obtained to evaluate for reflex sympathetic dystrophy, and demonstrated decreased tracer uptake in the bony skeleton of the bilateral lower extremities, reflective of diminished hydroxyapatite or bony remodeling (Fig 2). Plain films of her bilateral extremities were normal, showing no evidence of hyperostosis or periostitis. MRI of the lower extremities did not demonstrate any marrow signal abnormalities. Bone mineral densitometry was normal. Her laboratories were significant for normal calcium, magnesium, alkaline phosphatase, and normal creatinine with minimally elevated serum phosphorus at 4.6-5.5 mg/dL. Markers of bone turnover, including N-telopeptide in both the urine and serum, and Bone GLA, were normal. Vitamin D (25), D (1, 25), and PTH were normal. SPEP was negative. ESR was normal. Tubular resorption of phosphate (TRP) was found to be markedly elevated at 97 % (normal being 80-90%), making an unidentified primary defect in renal tubular phosphate excretion a possible explanation for the hyperphosphatemia, and a potential cause for her pain syndrome