Natural course and characteristics of cutaneous neurofibromas in neurofibromatosis 1

Neurofibromatosis 1 (NF1) is characterized by cutaneous, neurological and osseous manifestations. Most NF1 patients develop cutaneous neurofibromas. However, time-dependent change with aging and the predilection site of cutaneous neurofibromas remain unclear. To clarify the natural course and characteristics of cutaneous neurofibromas, a retrospective study was conducted for 57 NF1 patients who were treated at the Department of Dermatology of Tottori University Hospital between January 2007 and April 2016. For each patient, we investigated the time-dependent changes and the numbers of cutaneous neurofibromas in four body surface regions. There was a positive correlation between age and number of cutaneous neurofibromas (r = 0.75, P < 0.001). Cutaneous neurofibromas were located on the trunk (60.2%), lower limbs (16.1%), upper limbs (14.4%), and head and neck (9.2%). There was no significant relationship between each body type (e.g. obese or thin) and cutaneous neurofibromas. With respect to the year-to-year percentage change in cutaneous neurofibromas, the average annual rate of increase was 0.21 (range, -0.71 to 1.2). The number of cutaneous neurofibromas had increased in approximately 61% of the patients 1 year later. Our data will enable physicians to estimate the overall state of cutaneous neurofibromas in NF1 and will be useful for handling cutaneous manifestations before they become a serious condition.