Skeletal complications in the course of neurofibromatosis in children

Introduction
Type 1 neurofibromatosis (NF1) belongs to the group of phacomatoses characterised by the formation of neurofibromas in the course of the nerves. In some cases, it may also lead to lesser known skeletal symptoms such as disturbances in calcium-phosphate metabolism and decreased bone mineral density.

Aim of the study
The purpose of this work is to analyse possible skeletal complications in the course of neurofibromatosis, based on presentation of patients with NF1.

Material and methods
The study included 10 children diagnosed with NF1 (seven girls and three boys), aged four to 17 years. Medical examinations including evaluation of any motor system abnormalities, anthropometric measurements of body height and weight (to evaluate the respective parameters, centile charts were used from the OLAF project), and bone densitometry using dual-energy X-ray absorptiometry (DXA) were performed. Calcium and phosphate metabolisms were assessed based on laboratory tests (concentration of vitamin D – 25(OH)D, parathormone and alkaline phosphatase levels, and bone turnover markers).

Results
Decreased body height was found in half of the patients (5/10). Typical dysplastic bone lesions were observed in 3/10 children. On densitometry, in nine out of 10 examined children a Z-score decrease to < –1.0 was observed, and in five children this value was ≤ –2.0. Decreased 25(OH)D concentration was found in 7/10 examined children. In three out of 10 patients the osteocalcin level was increased.

Conclusions
NF1 may jeopardise normal development and function of the skeletal system in children – both of the mineral and bone metabolism. Assessment of the motor system and of the calcium and phosphate metabolism should be part of extended diagnosis and monitoring of this disease. Risk factors for bone fractures in children with NF1 are low bone mass and decreased vitamin D concentration.