Acanthosis nigricans

Acanthosis nigricans (AN) is a cutaneous disorder of hyperpigmentation and papillomatosis that may precede or coincide with a variety of benign, familial, or malignant disorders. Most cases of AN are the benign type and manifest as an autosomal dominant disease, a rare congenital disorder, or in association with obesity or diabetes. Patients who are affected usually present in childhood or adolescence with hyperpigmented velvety papillated plaques in flexural areas, such as the neck, axilla, groin, and fingers. Benign AN appears as velvety areas of hyperpigmentation in flexural regions of the body, and only rarely, when it manifests in a more exuberant fashion, will the umbilicus, areolae, or oral cavity be involved. Malignancy-associated AN (MAN) is hypothesized to be due to overproduction of an epidermal growth factor promoter secreted by the associated neoplasm. MAN is most commonly associated with adenocarcinoma of the stomach.

Oral manifestations are most common with MAN, but not the benign type of AN. They are present in 25-50% of patients with MAN. MAN may present with 3 other findings, which are cutaneous and oral papillomatosis, hyperkeratosis of the palms and soles, and a sudden eruption of seborrheic keratosis termed the Leser-Trélat sign. Recognition of these lesions could be vital in the early diagnosis of a potentially fatal adenocarcinoma of the GI tract.

The oral manifestations of MAN involve the lips, tongue, and palate. Gingival hyperplasia may also occur. Nonpigmented hypertrophy of the papillae along the dorsal surface and lateral edge of the tongue yield a characteristic fissured and shaggy texture. The lips are also subject to these papillomatous growths and swelling. The buccal mucosa shows some papillae, but, more commonly, velvety white plaques are present along with the uneven appearance. Interdental gingiva may become so hyperplastic that it interferes with eating as it covers the teeth.

Histologically, the benign and malignant forms of cutaneous AN are not different. Characteristic morphology includes an increase in surface keratin deposits, acanthosis hyperplasia of melanocytes in the spinous layer, and increased melanin deposition in the basal cell layer. Unlike the cutaneous areas of hyperpigmentation, oral lesions do not share the increased deposition of melanin.

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