Complete Guide to Acanthosis Nigricans 

• Acanthosis nigricans is a pigmentary disorder that causes dark plaques to develop in body folds and creases
• It is most often caused by obesity and a condition called insulin resistance
• Weight loss is the most effective way to treat obesity-related acanthosis nigricans
• Other treatments include topical creams, oral medications and laser therapy

Acanthosis nigricans is a skin condition in which dark, thickened, velvety patches of skin develop on the body, usually in creases or folds. It is most often caused by obesity and type 2 diabetes.

Treatment involves identifying and managing the underlying disorder. There are also several treatments available to improve the appearance of skin including keratolytics, depigmenting creams, laser therapy and chemical peels. 

What Is Acanthosis Nigricans?

Acanthosis nigricans is a skin condition that is most commonly caused by insulin resistance and obesity but is also associated with hormonal disorders, reactions to certain medications and less often, cancer. It is characterized by darkening and thickening of the skin.

This skin condition typically occurs in those under the age of 40 and is more common among skin of color than those with lighter skin tones, such as Caucasians or Asians. Other than possible itchiness, there are usually no other symptoms that accompany this condition.

Skin changes first present as gray-brown or black pigmentation that is dry, rough and thick, and covered with small growths called papillomatous lesions. These are responsible for the velvety texture of the plaques.  Over time, larger wart-like growths can develop. 

While acanthosis nigricans itself is not cause for alarm, it can indicate an underlying health problem and serve as an important warning sign for type 2 diabetes or polycystic ovary syndrome (PCOS).  

Common areas where it appears 

Lesions most often occur in skin folds; for example, on the neck, armpits (axillae) and groin, with the neck being the most common area. They can also develop in creases behind the knees, at the elbows or under the breasts. 

Causes and Risk Factors

One factor linked to causing this condition is thought to be higher levels of insulin which stimulate insulin-like growth factor 1 (IGF-1) receptors on skin cells which results in abnormal cell growth. In a process called hyperkeratosis, the outer layer of skin thickens, and for skin of color which naturally has more pigment, this buildup causes darker patches of skin.      

Diabetes

There is a common link between obesity, diabetes and acanthosis nigricans and this is related to issues with insulin. People with type 2 diabetes have hyperinsulinemia (high insulin levels) and insulin resistance, meaning their cells don’t respond normally to insulin. 

Insulin resistance leads to glucose and insulin levels that are higher than normal. Without treatment, type 2 diabetes is likely to develop. In individuals with acanthosis nigricans, the severity of their skin condition may be linked to how high their insulin levels are. 

Rarer causes

In addition to obesity and insulin resistance, several other medical conditions and causes have also been linked to this skin condition.

• Hormonal disorders such as Cushing’s syndrome, polycystic ovary syndrome (PCOS) and Addison’s disease 
• Metabolic syndrome is associated with obesity and insulin resistance, as well as increased cholesterol and blood pressure 
• Drug-induced acanthosis nigricans has been strongly linked to nicotinic acid and insulin; other medications include steroids and oral contraceptives 
• Cancer has been associated with acanthosis nigricans and include cancers of the internal organs (e.g., gastric adenocarcinoma, ovarian cancer) or lymphoma   

Picture of Acanthosis Nigricans 

Acanthosis nigricans is characterized by symmetrical, hyperpigmented plaques of skin that are velvety in texture. These plaques are thick and covered with small growths, and with time larger growths can develop. They most commonly occur in body creases and folds. 

Similar conditions

• Fungal infections such as tinea versicolor interfere with normal pigmentation of the skin and cause extensive dark or scaly patches on the body 
• Melasma is a pigmentation disorder that causes irregularly shaped dark patches of skin on the face, neck and chest 
• Postinflammatory hyperpigmentation (PIH) refers to darkened areas of skin that remain once inflammation from a skin injury or condition has resolved. 

Treatment Options

Because acanthosis nigricans is usually a sign of an underlying medical problem—most often insulin resistance—the main goal is to identify and treat the underlying issue. This can mean weight loss and dietary changes for those who are obese or treatment of the primary condition.

As well, there are also treatment options available to improve the appearance of the skin. These include topical creams, oral medications and cosmetic procedures.

Lifestyle changes

Successful weight loss can bring a dramatic change to skin along with a wealth of health benefits. Lifestyle changes such as diet and exercise may be recommended as well as medications prescribed for weight loss. Bariatric surgery is another option to help with obesity.

Losing weight has been shown to normalize blood glucose levels. In one study, researchers found that for people with type 2 diabetes, 36% could achieve remission at 24 months, due to weight loss.

Topical creams 

There are several topical creams available to improve the appearance of plaques.

Hydroquinone

Hydroquinone is a topical application that can lighten the skin by inhibiting melanin synthesis. Frequently, this compound is used alongside a retinoid and corticosteroid for greater results. 

Retinoids

Retinoid creams, such as adapalene and tretinoin, can effectively improve the appearance of hyperpigmented patches by lightening the skin. They do so by encouraging skin cell turnover and by hindering melanin production.

Vitamin D 

Calcipotriol D is a vitamin D derivative that is termed an antiproliferative; as such it inhibits proliferation of  keratinocytes, the skin cells that store pigment which is responsible for skin’s color. 

Cosmetic Procedures

Several professional procedures can effectively reduce the appearance of dark patches of skin and reduce thickened skin.  

Chemical peels

Chemical peels using trichloroacetic acid have been demonstrated to reduce hyperpigmentation and thickening of skin to improve skin’s appearance. 

So too has a combination of salicylic acid and mandelic acid peel along with maintenance therapy using a topical cream. In one study using this combination 100% of patients showed a significant improvement in both pigmentation and thickened skin. 

Laser treatments

Several types of laser treatments have been successful in treating acanthosis nigricans and one such type is fractional lasers to smooth skin and reduce hyperpigmentation.  

Another laser treatment that uses the mineral alexandrite to break down melanin has been shown to be successful in reducing dark patches as well. One study achieved more than a 95% clearance after 7 sessions with no recurrence after 2 years. 

Other treatments 

Oral retinoids are typically used for treatment-resistant cases as they are associated with side effects.

Oral retinoids

Oral retinoids treat acanthosis nigricans by normalizing epithelial growth and suppresses keratinocyte proliferation. Large doses are typically required and results are not immediate; symptoms may return once the medication is stopped.

Oral retinoids include:

• Acitretin
• Etretinate
• Isotretinoin

Metformin

Metformin is an antidiabetic drug that has also been shown to be effective in treating skin disorders, including acanthosis nigricans. Not only does metformin improve the appearance of skin, it also helps treat insulin resistance. Metformin has other advantages: it can also lower blood sugar and aid in weight loss.

When to See a Doctor

If you notice any change in your skin or if you suspect you may have acanthosis nigricans, it is advised to consult with a health care professional, who can examine your skin and if needed, order some tests.

You may be tested for insulin resistance or type 2 diabetes which blood tests to evaluate blood sugar and insulin levels.

If you are concerned that your medication is causing acanthosis nigricans, be sure to check with your healthcare provider before making any medication changes. 

Takeaway

Acanthosis nigricans is a pigmentary disorder that is characterized by dark, thick, velvety patches in skin folds. It is commonly caused by obesity and insulin resistance; it is also linked to hormonal disorders, drug reactions and to a lesser extent, cancer. 

While this skin condition is not cause for concern, anyone with suspected acanthosis nigricans should be evaluated by a health care professional to determine if an underlying disease may be causing it. 

Identification and successful treatment of the primary condition should resolve this pigmentary disorder. Several treatments are also available to reduce the appearance of  dark, thickened plaques including topical and oral medications, as well as chemical peels and laser therapy.