Nevus Sebaceous Syndrome

Nevus sebaceous (NS) is a hamartomatous disorder of the skin and adjacent tissues characterized by epidermal, follicular, sebaceous, and apocrine gland abnormalities. It occurs in approximately 1 in 1,000 live births. A hyperactivation of Ras pathways has been recently assumed to be the cause of this phenotype. NS lesions may be isolated or coupled with extracutaneous manifestations, mostly of the central nervous, ocular, and skeletal systems, or kidneys; in this case, the term NS syndrome is used. Cutaneous distribution of NS usually follows the linear patterns known as lines of Blaschko, with lines that do not follow the segmental trajectory of the peripheral sensory nerves but instead reflect the streams or trends of growth of embryonic tissues. Histological characteristics of the lesions appear to be actually more decisive than the clinical evaluation to distinguish between the types of epidermal nevus: the typical NS has both papillated epidermal hyperplasia and a predominance of subjacent abnormal follicular-sebaceous glands. Seizures, mental retardation, and/or cognitive developmental delay are the most common neurologic abnormalities associated with NS and usually are present within the first months of life; eye and skeletal involvement may be present as well. The definitive treatment of NS is full-thickness excision. However, the necessity and timing of excision to prevent possible future malignancy are not clear; lasers and photodynamic therapy are alternatives currently being explored for the treatment of NS, with varying degrees of success.