What is it?
Acanthosis nigricans is a skin condition in which the skin in the armpits, around the neck, in the groin and under the breasts becomes thickened and has a dark velvety appearance.
What causes it?
The cause of acanthosis nigricans is not completely understood. It is most frequently seen in overweight patients in whom it is believed to be related to insulin resistance. It can affect 20% of overweight adults and develop in overweight children. The thickened skin is not itchy or sore. This condition is frequently more severe in patients with darker skin colouring.
Endocrine or metabolic disorder(s) – including diabetes mellitus, metabolic syndrome, Cushing syndrome or polycystic ovarian syndrome and thyroid disease can be associated with acanthosis nigricans.
Medications may cause acanthosis nigricans as a side effect. Medications linked to acanthosis nigricans include glucocorticoids, insulin, oral contraceptives, testosterone and aripiprazole nicotinic acid.
Very rarely, sudden onset and widespread acanthosis nigricans involving hands and feet (particularly in a patient who is unwell and has lost weight) may be a manifestation of malignancy associated acanthosis nigricans. The cancers are most frequently in the gastrointestinal tract.
There are some rare inherited causes of acanthosis nigricans. The changes usually develop in early childhood and may be accompanied by other abnormalities in growth and other organs.
What does it look like?
Acanthosis nigricans typically appears as symmetrical thick, raised velvety areas of skin, grey-brown in colour and darker than the surrounding skin. Typically, the back and sides of the neck, underarms and groin are involved. Other skin fold areas can also be affected. Lesions can also occur on the knuckles of the hand, soles of the feet, knees and elbows though this is rare. Frequently many skin tags develop in the affected areas.
It is not uncommon for skin tags to be present in or around the affected area. In rare cases, acanthosis nigricans can appear on mucosal surfaces such as the mouth.
What other problems can occur?
The skin changes of acanthosis nigricans rarely causes complications, however, scratching or excessive scrubbing of the area can cause breaks in the skin and infection.
How is it diagnosed?
The diagnosis is usually made by a dermatologist after taking a history and examining the skin. A skin sample may be taken when the diagnosis is uncertain. As acanthosis nigricans usually indicates an underlying disease process, other tests looking for a disease such as diabetes or insulin resistance may be performed.
How is it treated?
Management of acanthosis nigricans involves correcting the underlying cause.
Weight loss in obese patients can result in significant improvement of lesions or complete resolution. Other treatments may be trialled by your dermatologist. These include topical retinoids or Vitamin D analogues. Lasers have been used to thin the thickened area in a small number of cases.
Things to avoid
People with acanthosis nigricans can sometimes mistakenly believe the skin to be dirty or able to be removed by excessive scrubbing of the affected areas. This should be avoided as it can cause further thickening and darkening of the skin.
What is the likely outcome?
The skin changes in acanthosis nigricans are long lasting and symptomless. On their own the changes in the skin do not normally have long-term physical consequences.
The underlying medical problems need to be identified and remedied. Those with insulin resistance and obesity related acanthosis nigricans are at higher risk of poorer adverse long term health outcomes if they develop diabetes mellitus and associated heart and kidney complications.
In inherited disorders associated with acanthosis nigricans treatment is directed at improving the cosmetic appearance.
The outcome for patients with malignant acanthosis nigricans is often poor.
This information has been written by Dr Artiene Tatian and Dr Deshan Sebaratnam
Last updated 03 April 2018