Linear Nevus Sebaceous Syndrome (LNSS) / Schimmelpenning Syndrome

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By Liji Thomas, MD

Linear nevus sebaceous syndrome (LNSS) is known by several other names, including Jadassohn nevus phakomatosis, Schimmelpenning-Feuerstein-Mims syndrome, and simply Schimmelpenning syndrome.

Clinical Features

LNSS is characterized by the presence of a linear sebaceous nevus with involvement of other systems, in particular the eye, the brain, and the bones. Mental disability and epileptic seizures are often present, and other organs may also be affected.

Sebaceous Nevus

The sebaceous nevus is usually large and may contain other abnormal cells. it is most often found on the scalp, the face, or the neck. While often unnoticed at birth, it becomes active and enlarges with the onset of puberty, appearing rough and warty, scaling, or thickened. By itself it does not produce any symptoms.

Central Nervous System

The linear sebaceous nevus is associated with various central nervous system anomalies, such as seizures, mental retardation, or hemimegalencephaly. Vascular anomalies of the cerebral vessels and malformations of various parts of the brain have also been reported.

Bone Deformities

The affected individual may have impaired bone formation, leading to dysplasia or hypoplasia of various bones including the skull and long bones. A special type of this syndrome is associated with hypophosphatemia and vitamin D-resistant rickets, which manifests with bowing of the legs, bone pain, height loss, and multiple fractures of the ribs and bones.

Heart Defects

Cardiac defects such as coarctation of the aorta have also been known to occur.

Ocular Changes

There may also be ocular signs and symptoms such as strabismus, coloboma, or missing parts of the iris, lenticular cataracts, vascular malformations of the eye, or retinal defects.

Cancers

Certain malignant tumors may also occur at a higher frequency in this syndrome with age. They include basal cell or squamous cell carcinomas of the skin.

Other Syndromes Associated with Sebaceous Nevi

Certain other conditions are also found to be present along with a sebaceous nevus, such as:

Phacomatosis Pigmentokeratotica

This syndrome consists of a sebaceous nevus with speckled lentiginous nevus, often associated with other anomalies such as neurological and skeletal defects.

Didymosis Aplasticosebacea

Here a sebaceous nevus occurs along with aplasia cutis congenital, usually of the scalp.

SCALP syndrome

This is a syndrome comprising sebaceous nevus, central nervous system defects, aplastia cutis congenita, limbal dermoid, and pigmented nevus.

Etiology

Schimmelpenning syndrome is caused by sporadic (not inherited) somatic mutations in a cell belonging to the ectodermal germline in the embryo. This is a post-zygotic mutation, and usually affects the HRAS, KRAS and NRAS genes. The presence of mosaicism in this condition refers to the occurrence of the mutation in only some cells but not all, that is, the presence of more than one cell line in the same individual.

Diagnosis and Management

Diagnosis of sebaceous nevus syndrome is made on the basis of the clinical manifestations of a sebaceous nevus, with involvement of the central nervous system or other organ systems. Testing is often required to identify other lesions in an individual with a large sebaceous nevus with any other clinical features. Management is symptomatic and may include attention to bony changes, visual alteration, and remedial education. Anti-epileptic medication may be required to control seizures. Removal of the nevus is recommended in case of cosmetic indications, as well as if there is any suspicion of malignant change.