Author: Vanessa Ngan, Staff Writer, 2004.
Acanthosis nigricans is a skin disorder characterised by darkening (hyperpigmentation) and thickening (hyperkeratosis) of the skin, occurring mainly in the folds of the skin in the armpit (axilla), groin and back of the neck.
Acanthosis nigricans is not a skin disease per se but a cutaneous sign of an underlying condition or disease.
There are two important types of acanthosis: benign and malignant. Although classically described as a sign of internal malignancy, this is very rare. Benign types, sometimes described as ‘pseudoacanthosis nigricans’ are much more common.
The cause for acanthosis nigricans is still not clearly defined but it appears to be related to insulin resistance. It has been associated with various benign and malignant conditions. Based on the pre-disposing conditions, acanthosis nigricans has been divided into 7 types.
|Types of acanthosis nigricans|
|Obesity-associated acanthosis nigricans||
|Syndromic acanthosis nigricans|
|Benign acanthosis nigricans||
|Drug-induced acanthosis nigricans||
|Hereditary benign acanthosis nigricans||
|Malignant acanthosis nigricans||
|Mixed-type acanthosis nigricans||
It is very important to differentiate acanthosis nigricans related to malignancy from that related to benign conditions. Tumours in malignant acanthosis nigricans are usually very aggressive and spread quickly. Death often occurs soon after. If malignant acanthosis nigricans is suspected in a patient without known cancer, it is extremely important to perform a thorough workup for underlying malignancy and identify a hidden tumour. If the tumour can be successfully treated, the condition may resolve.
Other causes of acanthosis nigricans may be identified by screening for insulin resistance and diabetes mellitus.
The primary aim of treatment is to correct the underlying disease process. Often correcting the underlying cause results in resolution of the lesions.
In hereditary acanthosis nigricans, lesions tend to enlarge gradually before stabilising and/or regressing on their own.
There is no specific treatment for acanthosis nigricans. Treatments considered are used primarily to improve cosmetic appearance and include topical retinoids, dermabrasion and laser therapy.
Final outcome of acanthosis nigricans varies depending on the cause of acanthosis nigricans. Benign conditions either on their own or through lifestyle changes and/or treatment have good outcomes. However, the prognosis for patients with malignant acanthosis nigricans is often poor. The associated cancer is often advanced and the average survival of these patients is approximately 2 years.
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