Hypophosphatemic osteomalacia in neurofibromatosis 1 associated with intracranial gliomas and congenital renal agenesis: A rare case report and review of the literature

INTRODUCTION: Neurofibromatosis Type 1 (Nf1), also termed von Recklinghausen disease, is a rare autosomal dominant genetic disorder accompanied by several osseous and skeletal manifestations. In NF, hypophosphatemia linked to secondary hyperparathyroidism due to Vitamin D deficiency and low calcium intake has been reported as a risk factor for low bone mass density (BMD), but reports of NF1 associated oncogenic hypophosphatemic osteomalacia (HO) are extremely rare. CASE REPORT: We report a patient with NF1 associated with intracranial low-grade gliomas and congenital renal agenesis suffering from HO. Bone defects and deformities such as generalized bone pains located in feet, ankles and lower limbs, thoracic scoliosis, mild bowing of long bones of lower limbs, stress fractures, and old fractures as well as with altered bone metabolic serum markers were present. After 8 weeks of follow-up, it was observed that the combination of oral administration of phosphate and Vitamin D improved her medical symptoms without significant changes in phosphate levels or BMD. CONCLUSION: Although renal agenesis is not correlated with hypophosphatemia, the coexistence of NF1, renal congenital deformities, and low-grade gliomas may contribute to disease severity. Conventional treatment with high doses of oral calcitriol associated with phosphate is efficient to improve the clinical and laboratory symptoms of the disease.