Hypophosphatemic Osteomalacia associated with Neurofibromatosis Type-1: A case report and literature review

Abstract

Introduction: Skeleton abnormalities are not uncommon in neurofibromatosis type-1 (NF1), which usually manifest as congenital malformations, such as scoliosis and sphenoid wing dysplasia. However, very rare cases of NF1 have been associated with hypophosphatemic osteomalacia (HO), which is characterized with later onset in adulthood, severe hypophosphatemia and disorder of the mineralization of organic bone matrix. Patient concerns: Here we reported a rare case of a 29-year-old woman presented with weakness and pain in lower limbs for 18 months and aggravated for half a year. On physical examination, her lower limbs’ myodynamia reduced and tenderness in multiple bone areas was detected. Light brown patches and scattered nodules could be seen on her skin, and a soft subcutaneous mass was found in the low back. Laboratory evaluation showed hypophosphatemia. Bone ECT suggested multiple abnormal bone metabolism and MRI scan of lumbosacral spine revealed numerous fractures. Neuroimaging indicated the neurofibromas, and then the biopsy of the subcutaneous lump confirmed neurofibromatosis. Diagnosis: HO associated with NF1 was diagnosed, based on the presence of café-au-lait spots and the results of bone ECT scan and biopsy. Interventions: The patient was treated with oral calcitriol, calcium carbonate d3 and phosphorus, as well as intramuscular carbocalcitonin. Outcomes: During hospitalization, her serum phosphorus level increased and symptoms improved. Conclusion: The case reported here calls attention to that when NF1 patients manifested with weakness and neurology diseases have been excluded, HO should be taken into consideration.