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Comedo Nevus

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Comedo nevus (Nevus comedonicus), a lesion of the pilosebaceous unit, presents at birth or within the first two decades of life as a group of prominent comedones that are usually asymptomatic.

Location & Appearance: The comedones are unilateral and often arranged in a linear pattern on the skin of face, neck or upper trunk. Rare sites include inguinal region, palm and wrist. In rare cases, the comedones are more extensive with generalized distribution over the body. The lesions appear as slightly elevated papules with keratinaceous plugs mimicking comedones. Some cases show inflammatory changes, sinuses, fistulae and scarring.

Associated conditions: Comedo nevus may be associated with other skin conditions such as icthyosis, trichilemmal cysts, accessory breast tissue, hidradenoma papilliferum, syringocystadenoma papilliferum, pilar sheath acanthoma, basal cell carcinoma, and squamous cell carcinoma.

Nevus Comedonicus Syndrome: It consists of comedo nevus, spinal deformities (spina bifida, scoliosis, fused vertebrae, hemivertebrae), finger/toe deformities, cataracts, microcephaly, and seizures.

Molecular Genetics: Comedo nevus may be a mosaic form of Apert's syndrome. Nevus comedonicus syndrome shares many of the skeletal deformities with Apert's syndrome. Both conditions show a mutation in the fibroblastic growth factor receptor 2 (FGFR2). In comedo nevus, this mutation is not seen in the unaffected skin.

Microscopically, the epidermis is hyperkeratotic and may show a combination of atrophy and acanthosis. There are numerous cystically dilated hair follicles plugged with keratinaceous debris. Leakage of cyst contents into the surrounding may incite a granulomatous inflammation as well as foreign body giant cell reaction.

Case History: A 54 y/o male presented with lesions on the nape of his neck on the right side. They were associated with irritation and had been present for 5 years. There were no extracutaneous manifestations of nevus comedonicus syndrome. The image shows multiple honey comb-like linear pits (comedones) many of which are clearly plugged with keratinaceous material.

Case courtesy of: Dr. Sanjay D. Deshmukh (Professor of Pathology) & Dr. Vishal A. Indurkar (Associate Professor of Dermatology), Dr. Vithalrao Vikhe Patil Medical College and Hospital, Ahmednagar, India.

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