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Chapter 1. Acanthosis Nigricans

Definition

Pigmented plaques formed by confluence of smooth-surfaced soft papules, some of which may become polypoid, traversed by accentuations of skin folds. This disease has a predilection for intertriginous regions. The condition may develop consequent to obesity, an endocrine disorder, or a malignant neoplasm in an internal organ. Morphologically, i.e., clinically and histopathologically, the appearance of the altered skin is the same, irrespective of cause.

Course

Acanthosis nigricans tends to persist unless its cause is identified and corrected. For example, lesions of acanthosis nigricans secondary to an endocrine disorder, such as diabetes mellitus or hypothyroidism, disappear when that abnormality has been remedied by appropriate hormonal therapy. Lesions consequent to the effects of a malignant neoplasm in an internal organ, such as an adenocarcinoma of the stomach or the colon, may regress entirely after complete surgical extirpation of the inciting neoplasm, if that neoplasm has not yet metastasized.

Integration: Unifying Concept

Whether acanthosis nigricans is a consequence of an endocrine disorder or of a malignant neoplasm in an internal organ, the morphologic attributes are the same, clinically and histopathologically. When the cause of acanthosis nigricans is remedied, whether by treatment of the endocrine abnormality or by excision of a malignant neoplasm, the lesions of acanthosis nigricans wane and may disappear altogether.

The morphologic features of the confluent and reticulated papillomatosis of Gougerot and Carteaud seem to be those of a muted expression of acanthosis nigricans on an anterior aspect of the trunk.

The mechanism whereby acanthosis nigricans and its variants come to be formed is not known, but in some patients, evidence implicates insulin as an etiologic factor (insulin resistance). In patients with acanthosis nigricans who harbor an internal malignancy, humoral growth factors produced by the neoplastic cells may be important in the formation of the skin lesions.

Therapy

Treatment of lesions of acanthosis nigricans themselves is ineffective. Therapy must be directed at the pathologic process responsible for the development of acanthosis nigricans, such as obesity, an endocrinopathy, or an internal malignancy.

Distribution

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Fig. 1-1

Widespread acanthosis nigricans. This implies concurrence of an internal malignancy.


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Fig. 1-2

Confluent papillomatosis of the lips and buccal mucosa.


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Fig. 1-3

Bilateral involvement of the axillae in this obese young man with an endocrine disorder.


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Fig. 1-4

The neck is a favorite site.


Individual Lesions

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Fig. 1-5

Closely set tiny papules in linear array.


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Fig. 1-6

Lesions situated over joints. Note how dark are the fingers in contrast to the rest of the skin.


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Fig. 1-7

Pigmented plaque with mammillated surface.


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Fig. 1-8

Pigmented, slightly elevated plaque with a gently papillated smooth surface, in this instance punctuated by atrophic striae.


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Fig. 1-9

Polypoid excrescences, as well as subtle papules. Grooves that traverse plaques represent accentuation of skin lines.


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Fig. 1-10

Ill-defined plaque, thrown into folds, made up of prominent, smooth-surfaced papules, some of them polypoid.


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Fig. 1-11

Pigmented plaque in which skin folds are accentuated.


New! Additional Images

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Fig. 1-12

Acanthosis nigricans: Brown papules, some of which have become confluent to form a plaque, are intersected by lines normal for skin. The dark brown macule is a Clark’s nevus.