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Linear nevus sebaceus syndrome
Linear nevus sebaceous syndrome (LNSS) is characterized by the association of a large sebaceous nevus, usually appearing on the face or on the scalp, with a broad spectrum of abnormalities that may affect every organ system, including the central nervous system (brain neoplasms, hemimegalencephaly and lateral ventricle enlargement).
The incidence of sebaceous nevi at birth is estimated at 1 in 1000 but the prevalence of these lesions in association with other anomalies, as in the case of LNSS, varies between case reports to around 1:10,000.
Although the terms ``epidermal nevus syndrome'' and ``linear nevus sebaceous syndrome'' are often used interchangeably, epidermal nevus syndrome refers to a group of diseases characterized by the association of all varieties of epidermal nevi with other organ involvement. LNSS strictly applies to patients with a typical midline nevus for which three dermatologic stages have been identified. In stage 1, lasting from birth to puberty, the lesion is small and hairless, and may regress in size. Stage 2 occurs during puberty, and is characterized by gland enlargement and the epidermis becoming verrucous. During stage 3, there is possible malignant transformation of the lesion, with the most common pathology being basal cell epithelioma. The main neurological manifestations are seizures (up to 75% of patients) and intellectual deficit (up to 60% of patients). Many other organ systems may also be involved in this syndrome, including the cardiovascular (aortic coarctation), skeletal (localized cranial fibrous dysplasia, skeletal hypoplasia, formation of bony structures, scoliosis and kyphoscoliosis, vitamin D-resistant rickets and hypophosphatemia), ophthalmologic (strabismus, retinal anomalies, coloboma, cataracts, corneal vascularization, and ocular hemangiomas) and urogenital (horseshoe kidney) systems.
LNSS is a sporadic disease. It is hypothesized that the epidermal nevus syndromes are the result of genetic mosaicism involving a dominant gene.
Due to the potential for multisystem organ involvement, all children with a suspected diagnosis of LNSS should undergo a multisystem evaluation with imaging studies (CT or if possible MRI scanning of the brain), electroencephalogram in case of epilepsy, analysis of skin biopsies and ophthalmic investigation.
Differential diagnosis should include nevus comedonicus syndrome, Becker nevus syndrome, phakomatosis pigmentokeratotica, Proteus syndrome and CHILD syndrome (see these terms).
Management and treatment
The linear nevus sebaceous is usually asymptomatic but because of its cosmetic impact and malignant potential, prophylactic removal of the lesion (preferably before puberty, and sometimes even during infancy or early childhood) may be recommended. Care should be multidisciplinary including mainly orthopedic and ophthalmic follow up. Brain imaging studies should be performed when clinically indicated.
The prognosis depends on the severity of the clinical manifestations and the extent of the multisystem involvement.