Adult hypophosphataemic osteomalacia with Fanconi syndrome presenting in a patient with neurofibromatosis.

A patient is described with neurofibromatosis, increasing walking problems and low back pain. Initially, osteoporosis or pressure caused by a neurofibroma was suspected. However, the progressively increasing alkaline phosphatase activity and hypophosphataemia found during laboratory investigations led to metabolic studies which revealed proximal tubular dysfunction. A bone biopsy showed severe osteomalacia. A diagnosis of hypophosphataemic osteomalacia was made based on the Fanconi-syndrome. The association between hypophosphataemic osteomalacia and neurofibromatosis may be akin to the relationship between this type of osteomalacia and mesenchymal tumours, which has been noticed several times in the literature. The underlying mechanism is unknown.