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Acanthosis nigricans (AN) is a diffuse, velvety thickening and
hyperpigmentation of the skin, chiefly in axillae and other body
folds, the etiology of which may be related to factors of hereditary,
associated endocrine disorders, obesity, drug administration, and,
in one rare form, malignancy.
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- Type 1—Hereditary Benign AN No associated endocrine
disorder.
- Type 2—Benign AN Associated with insulin resistance
(IR): IR diabetes mellitus (DM), hyperandrogenism, acromegaly, gigantism,
Cushing’s disease, glucocorticoid therapy, diethylstilbestrol,
oral contraceptives, growth hormone, hypogonadism, Addison’s
disease, hypothyroidism.
- Type 3—Pseudo-AN Obesity-induced IR, darker skin
types.
- Type 4—Drug-induced AN Nicotinic acid, stilbestrol
in young males, oral contraceptives.
- Type 5—Malignant AN Paraneoplastic, usually adenocarcinoma;
less commonly, lymphoma.
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Age Any age. Peak: puberty to adulthood.
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Incidence 7% of the population.
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Race African Americans > Hispanics
> Caucasians.
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Epidermal changes of AN are likely caused by triggers that stimulate
keratinocyte and fibroblast proliferation. In type 2, benign AN,
the trigger is likely insulin or an insulinlike growth factor. In type
5, malignant AN, the trigger is likely the tumor or tumor secretions.
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AN has an asymptomatic, insidious onset. The first visible change
is darkening of pigmentation which gradually progress to velvety
plaques that may be pruritic.
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Color Dark brown to black, hyperpigmented,
skin appears dirty.
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Palpation Velvety, rugose, mammillated.
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Distribution Posterior neck (Fig.
18-1) > axillae, groin > antecubital, knuckles, submammary, umbilicus,
areola.
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Mucous Membranes Oral, nasal, laryngeal,
and esophagus: velvety texture with delicate furrows.
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Nails Leukonychia, hyperkeratosis.
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Other Skin tags in same areas.
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Ocular Papillomatous lesions on
the eyelids and conjunctiva.
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Benign AN Obesity or underlying
endocrine disorder.
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Malignant AN Underlying malignancy,
gastric adenocarcinoma (70%).
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Differential
Diagnosis
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AN can be confused with confluent and reticulated papillomatosis
of Gougerot and Carteaud (CRP), terre firme, hypertrichosis, Becker’s
nevus, epidermal nevus, hemochromatosis, Addison’s, or
pellagra.
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Laboratory Examinations
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Dermatopathology Papillomatosis,
hyperkeratosis; epidermis thrown into irregular folds, showing varying
degrees of acanthosis.
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- Type 1: Accentuated at puberty, and, at times, regresses
when older.
- Type 2: Prognosis related to severity of IR. AN may regress
subsequent to treatment of the IR state.
- Type 3: AN may regress subsequent to significant weight loss.
- Type 4: Resolves when causative drug discontinued.
- Type ...