follow @PCDSUKCreated: 3rd March 2015 | Last Updated: 30th December 2015
Introduction
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Acanthosis nigricans (AN) is characterised by hyperpigmentation and a velvety thickening of skin predominantly affecting the neck and flexures. In most individuals the condition is regarded as benign, although rarely it is associated with internal malignancy (malignant acanthosis nigricans), especially of the stomach. This chapter is set out as follows: |
Aetiology
Background
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AN has a number of aetiologies whose likely common mechanism is stimulation of tyrosine kinase growth factor receptor signalling pathways in the epidermis. In insulin resistance syndromes high levels of circulating insulin activate the insulin-like growth factor 1 receptor
Causal factors
There are numerous causes of AN, which may occur in isolation or in combination:
- Obesity - often caused by insulin resistance, is the most common cause of AN and usually arises in adults. The dermatosis is weight dependent, and lesions may completely regress with weight reduction
- Hereditary - AN can be inherited as an autosomal dominant trait
- Drugs - appear to be an uncommon cause, and include systemic corticosteroids, nicotinic acid and stilboestrol
- Acral AN - lesions are most prominent over the dorsal surface of hands and feet, and are much more common in darker-skinned individuals
- Malignant acanthosis nigricans - is associated with internal malignancy, usually a gastric adenocarcinoma, although many other carcinomata have been associated
History
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The age at which AN presents depends on the cause:
- In many cases the condition presents in adults
- In hereditary forms, AN tends to arise in childhood
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Malignant AN tends to develop in middle-aged and elderly patients, and is more abrupt in presentation
- The skin changes of AN tend to be asymptomatic, except in malignant AN
Clinical findings
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Distribution
- Symmetrical
- The most common sites are the intertriginous areas of the axilla, groin, anogenital region, and the back and sides of the neck. The neck is the most commonly affected site in children
- The dorsal surfaces of the hands, feet, elbows and knees are involved in acral AN
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Other sites may be affected, and occasionally AN can be widespread
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Morphology
- Lesions begin as hyperpigmented patches, which thicken with a velvety texture
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Many small, papillomatous lesions develop within affected areas
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Malignant AN
- Itch / irritation is common
- Lesions arise more suddenly, are more extensive and severe
- The mucosa, palms and soles are much more frequently involved, and papillomatous thickenings around the lips and eyes may be the presenting feature
- The vast majority of cases of malignant AN are secondary to adenocarinoma of the stomach, but other malignancies sometimes found include other GI tract tumours, lung, uterus, ovaries, and urinary tract
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Additional features that should increase the level of suspicion are:
- Tripe palms, which denotes velvety, rugose thickening of the palms, and is nearly always associated with internal malignancy, usually the stomach or lungs
- The Leser-Trélat sign, characterised by the abrupt appearance of multiple, and sometimes itchy, seborrhoeic keratoses that rapidly increase in their size and number, is also associated with malignancy, usually of the stomach or colon
- Florid cutaneous papillomatosis (FCP), characterised by the rapid onset of numerous warty papules on the trunk and the extremities that are clinically indistinguishable from viral warts, is usually associated with gastric adenocarcinoma
Images
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Figure: 1 AN in the axilla |
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Figure: 2 AN on the neck |
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Figure: 3 Hereditary AN |
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Figure: 4 AN on the elbows |
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Figure: 5 Acral AN in a diabetic patient |
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Figure: 6 Same patient as above |
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Figure: 7 Malignant AN
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Figure: 8 Malignant AN associated with gastric carcinoma |
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Figure: 9 Malignant AN associated with carcinoma of the uterus Copied with kind permission from Dermatoweb |
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Figure: 10 Same patient as above |
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Figure: 11 Malignant AN |
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Figure: 12 Tripe palms Secondary to carcinoma of the bronchus |
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Figure: 13 Same patient as above |
Investigations
- In the majority of patients it is important to test for diabetes mellitus
Management
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There is no useful dermatological treatment for AN
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The primary aim is to correct the underlying cause, which, if possible can lead to an improvement in symptoms:
- Weight loss
- Correct hyperinsulinaemia through diet and medication
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Stop any causal medication in drug-induced AN, if possible
- Patients with suspected malignant AN need urgent referral as a 2 Week Rule. Such patients need a thorough workup for underlying malignancy, although occasionally malignant AN can precede internal manifestations