Acanthosis nigricans is a skin condition where there is the appearance of dark brown to black patches on the skin. This darkening is known as hyperpigmentation. The affected part of the skin might have a velvety appearance. Usually the skin in the body folds are affected, like the neck, armpit, groin and forehead. It may be accompanied by a foul odor. As such there is no specific treatment for acanthosis nigricans but treatment of the underlying cause leads to improvement of the affected area to some extent.
Broadly acanthosis nigricans can be divided into two types – benign and malignant – depending upon the underlying causes.
The benign form of acanthosis nigricans occur due to excessive body weight, family history of acanthosis nigricans and in people having hormonal problems like hypothyroidism (underactive thyroid) and insulin resistance. It usually develops gradually over months and years.
The malignant form of acanthosis nigricans is found in patients with cancerous tumours of the internal organs like the stomach, colon and liver. This variety of acanthosis nigricans may occur before or after the occurrence of the tumour. Another characteristic feature of this variety is that the onset and rate of progression is very rapid.
The change in the skin is the only presenting symptom of acanthosis nigricans. However, it is not only the colour that changes. There may also be changes in the appearance and texture of the skin. All these changes usually progress gradually over months to years. Sometimes there may be associated bad smell and itchy sensation but most people do not experience any itch.
Commonly affected areas include the neck folds, armpits, groin area, forehead, skin over the joint areas of fingers (knuckles) and toes. Rarely the lips, soles, palms and even the skin on other areas of the body may be affected. Depending on the cause of acanthosis nigricans, there may also be other symptoms of the causative condition.
For example, there may be darkening of the skin with weight gain, constipation and fatigue in hypothyroidism.
The exact cause of acanthosis nigricans is not known but it tends to arise secondary to a number of known diseases. Common conditions include:
- Diabetes especially the insulin resistance.
- Excessive body weight – being obese or overweight.
- Hormonal disorders including:
– Polycystic ovarian syndrome (PCOS)
– Cushing’s disease and other adrenal gland disorders.
– Growth hormone disturbances.
- Cancer involving the stomach, liver, ovary, breast or prostate or tumors of lymph nodes (lymphoma).
- Intake of certain drugs like glucocorticoids, nicotinic acid, growth hormone, stilbesterol and so on.
- Genes(familial variety) may also lead to acanthosis nigricans from birth or during childhood.
There is no specific treatment for the darkening of the skin itself. Sometimes laser therapy is used to reduce skin thickness and antibacterial soaps are prescribed to control the bad smell. Treatment of acanthosis nigricans involve management of underlying condition like losing weight in obese patients, taking drugs to control hormonal disorders like polycystic ovarian syndrome or hypothyroidism, and even surgical removal of cancerous tumor. These measures may help in improving the skin appearance but treatment is primarily indicated for managing the underlying condition first, rather than just to treat the skin changes.