Segmental distribution of nodules on trunk
The lesions on this patient’s trunk had been growing in size—and number—over the past 42 years. The pattern of these lesions proved helpful in making the diagnosis.
Diagnosis: Segmental neurofibromatosis
Dermatopathologic evaluation of the tissue sample indicated that the lesion was a neurofibroma, and clinical correlation fine-tuned the diagnosis to segmental neurofibromatosis (NF). The diagnosis of segmental NF is clinical with biopsy to confirm the lesions are neurofibromas. Segmental NF is a mosaic form of neurofibromatosis type 1 (NF1) that results from a postzygotic mutation of the NF1 gene. While NF1 is a relatively common neurocutaneous disorder that occurs with a frequency of one in 3000,1 segmental NF is more rare, with an estimated prevalence of one in 40,000.2
NF1 often follows an autosomal dominant inheritance pattern, although up to 50% of patients with NF1 arise de novo from spontaneous mutations.3 NF1 is characterized by multiple café-au-lait macules, axillary freckling, neurofibromas, and Lisch nodules (pigmented iris hamartomas).
Systemic findings that are associated with NF1 include malignant peripheral nerve sheath tumors, optic gliomas, and vasculopathy.3 While patients with segmental NF may exhibit some of these same findings, the distribution of neurofibromas is often limited to one dermatome. Additionally, patients with segmental NF typically do not exhibit extracutaneous lesions, systemic involvement, or a family history of NF.
Rule out these dermatomal lesions
This case highlights a unique pattern of neoplasm development along a dermatome, an area of skin where innervation derives from a single spinal nerve. Symptoms that follow a dermatome often point to a pathology involving the related nerve root.
This differs from Blaschko lines, which form a specific surface pattern that is believed to reflect the migration of embryonic skin cells. Blaschko lines do not follow any known vascular, nervous, or lymphatic structures of the skin. Interestingly, when patients with segmental NF have associated pigmentary lesions, such as café-au-lait macules, these lesions may border Blaschko lines.
