Acanthosis nigricans: warning signs on the neck

A gray-brown color in the neck or along the bends of the joints? This can be due to the type. The discoloration can also indicate illnesses. Why sufferers should see a doctor

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Has the hair dye reacted with the skin? Does the collar of the newly acquired shirt rub off? Sometimes dirty gray spots on the neck are a mystery to those affected. Especially if they cannot be rubbed off despite intensive washing and brushing. The same spots can appear on the armpits or groin, wherever skin rubs against skin. Although the sight is annoying, very few consider it a reason to see a doctor. But that would be important to rule out diseases that can cause this discoloration.

"Often the patients come to us for a different reason, and I happen to find the discoloration as a secondary finding," says Professor Eggert Stockfleth, Director of the Dermatology Clinic at the Ruhr University in Bochum. This is an extensive, increased pigmentation and keratinization of the skin. Usually it occurs symmetrically. Physicians used to call it "black skin", today it is called Acanthosis nigricans. Several internal diseases can trigger the skin change. If the discoloration is rather diffuse, doctors speak of pseudoacanthosis nigricans. This sub-form particularly affects more heavily pigmented people with a higher body weight and, apart from the problems caused by obesity, usually has no pathological causes.

Acanthosis nigricans on the neck

© Mauritius / Alamy

Tissue sample for diagnosis

Acanthosis describes a thickening of the prickly cell layer in the epidermis, while nigricans means "blackish". The discoloration is therefore due to the fact that many pigmented cells have formed on the affected areas. A punch biopsy can show whether the skin is actually changed in this way. To do this, the dermatologist first numbs the area with a syringe, then takes some skin that is examined.

"The examination is necessary because a number of other skin diseases can cause a similar complexion," says Stockfleth. These include large birthmarks, fungal diseases, pemphigus, Darier's disease (dyskeratosis follicularis) or T-cell lymphomas, i.e. certain forms of leukemia. Atopic eczema in the context of neurodermatitis can also look similar on dark skin.

Often problems with insulin levels

If it is acanthosis nigricans, the doctors investigate why the skin cells in the prickly cell layer have increased. "We don't always find a reason," explains Stockfleth. But often, excess insulin stimulates skin cell growth. For example, increased insulin levels can be an indication of type 2 diabetes. Or to a preliminary stage of diabetes, insulin resistance: the cells of the muscles, the liver and the adipose tissue respond less to insulin, which is why the pancreas releases more insulin into the blood. Another cause of increased insulin levels can be an insulinoma. This is a hormone-producing tumor in the pancreas that releases insulin in an uncontrolled manner. Doctors therefore take blood to identify glucose metabolism disorders and other hormonal disorders.

Exclude tumors

A genetic predisposition can also be the reason for acanthosis nigricans. In rare cases, however, it is also the side effect of a malignant disease, especially tumors of the gastrointestinal tract. "For this reason, the search for a possible cancer is usually an integral part of the examinations," says Stockfleth. The determination of tumor markers in the blood such as CEA and alpha-1-fetoprotein can provide initial clues. Further examinations include gastroscopy and colonoscopy, an ultrasound of the abdomen and x-rays. Lungoscopy and laparoscopy are also possible.

Medicines can also cause changes in the skin: "Above all, substances that interfere with lipid metabolism," says Stockfleth. These include, for example, corticoids such as cortisone, nicotinic acid, birth control pills and fusidic acid.

Therapy depending on the cause

Treatment for acanthosis nigricans depends on the cause. If drugs are the trigger, the doctor will replace them if possible. If there is a preliminary stage of diabetes, Stockfleth advises patients to exercise more, eat more consciously and thereby lose weight. "If the insulin resistance regresses as a result, the chances are good that the discoloration will also decrease," explains the expert. It is similar when other causes are eliminated.

If the skin changes persist anyway, dermatologists use external agents. Zinc-containing powder can dry out the affected areas, salicylic and urea-containing creams soften them, and low-dose vitamin A acid is said to lighten the skin areas. If the skin grows heavily and looks wart-shaped, doctors can remove the affected areas with a small operation. However, the skin changes may reappear after a few months. Usually, health insurance companies will cover the cost of the procedure. If you want to be on the safe side, submit an application in advance.