Acanthosis nigricans is the result of a hereditary predisposition or associated with some internal cancers, endocrine disturbances, certain medications or obesity. People with acanthosis nigricans are known for their resistance to insulin in diabetics. Sudden appearance of acanthosis nigricans at any age calls for a thorough investigation of body systems to rule out any underlying cancers.
What is the Cause for Acanthosis Nigricans?
As mentioned above, there are many causes for acanthosis nigricans. According to the underlying cause, acanthosis nigricans may be divided into five different types.
- Hereditary Benign Acanthosis Nigricans. This type runs in families and there is usually no associated endocrine disorder. Hereditary acanthosis nigricans usually appears at birth or in early childhood. The skin features may increase at puberty, though many may regress later with age.
- Benign Acanthosis Nigricans. This is associated with certain endocrine disorders. Insulin resistance is an underlying condition in benign acanthosis nigricans. The important hormonal disorders associated with acanthosis nigricans are diabetes, increased androgen secreting tumors, acromegaly or gigantism, Cushing’s syndrome, Addison’s disease , hypothyroidism etc. Course and progression of the disease depends upon the management of underlying disturbance.
- Pseudo-acanthosis Nigricans. Pseudo-acanthosis nigricans is associated with obesity. It starts after puberty and has a direct relationship with increasing weight. It is common among the dark skinned. Insulin resistance is common in pseudo-acanthosis nigricans. Regression of the dark velvety skin is seen with significant reduction of weight.
- Drug induced Acanthosis Nigricans. High dose nicotinic acid, stilbesterol in young males, systemic steroid therapy, certain oral contraceptive pills and growth hormone therapy are some of the causes for drug induced acanthosis nigricans.
- Malignant Acanthosis Nigricans. Acanthosis nigricans could be a forerunner of underlying cancers within the gastrointestinal or genitourinary systems. Less commonly it may be associated with lymphomas. In certain malignancies, acanthosis nigricans may precede the appearance of tumors as early as five years. Successful treatment of the underlying malignancy usually results in complete regression of acanthosis nigricans.
The typical skin features of thickening and dark pigmentations in acanthosis nigricans are caused by certain chemicals secreted by the tumors or due to the effect of hormones, including insulin, on the skin fibroblasts and melanocytes.
How is Acanthosis Nigricans Diagnosed?
Acanthosis nigricans has to be differentiated from confluent and reticulated papillomatosis, pigmented pityriasis versicolor, X-linked Icthyosis, retention hyperkeratosis and excessive nicotinic acid ingestion. Diagnosis of acanthosis nigricans is mainly from the history and clinical presentations.
A complete workout including a hormonal profile, blood sugar, biopsy of the skin and histopathological study and, in case of suspected malignancy, a full body imaging and endoscopy is called for in acanthosis nigricans.
Clinical Features of Acanthosis Nigricans
Irrespective of the cause, all varieties of acanthosis nigricans show a dark pigmentation and thickening of the skin, usually in a symmetrical manner, on the neck, armpits, groins, elbows, behind the knees, around umbilicus and in the perianal region. Skin looks dirty and the surface is wavy and rugose with a velvety appearance. Skin lines show up prominently.
In acanthosis nigricans associated with obesity, the dark, thickened and velvety patches are more pronounced on the apposed surfaces of the folds, especially the thighs. Skin tags appear in large numbers in these patients.
In the severe malignant type, all features of acanthosis nigricans are accentuated: the skin is more thickened, dark and velvety and there is often involvement of the palms, soles, oral cavity and the edges of the lips.
Awareness on how to manage acanthosis nigricans is essential in preventing the serious consequences of this skin marker of internal malignancies.
Sources:
- Pavithran K et al. Disorders of Keratinization. IADVL Textbook of Dermatology. Eds, Valia RG & Valia AR. 3:995-1069; 2008.
- Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology, Fifth Ed, 2005
Disclaimer
The information given in this article is for educational purpose only so that patients are aware of the options available. No diagnosis should be made or treatment undertaken without first consulting your doctor. If you do so, the author or suite101 will not be responsible for any consequences. The images provided are for illustration purpose only.
Hanish Babu - Dr.Hanish Babu, MD is a dermatologist and a feature writer on Suite101.com with more than 200 articles related to skin diseases on the ...
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