A dark, thick, velvety patch of skin in the folds on the back of the neck is called acanthosis nigricans. It is most common in darker-skinned individuals, and often asymptomatic. While it is usually associated with a variety of medical conditions and obesity, it can be hereditary and not associated with disease. However, it can be a marker for a more serious condition, and should be evaluated by a doctor.
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Usually this skin change is gradual over months to years; you may not even notice it right away because it often does not hurt, itch or bleed. Sometimes other areas of the body are also affected including your armpits, groin and neck, or even your palms, lips and the soles of your feet. In rare cases, there can be severe itching and this is usually associated with the malignant type that is seen with cancers.
Hormonal conditions, obesity and diabetes are most often associated with this darkness of the skin and its presence can lead to their diagnosis. The high insulin levels and the insulin resistance that occurs in type 2 diabetes or these other metabolic conditions like polycystic ovarian disease (PCOS) is the cause of the skin changes. In a study done by the Annals of Family Medicine in 2007, individuals aged 7 to 39 with acanthosis nigricans were almost twice as likely to have type 2 diabetes.
Certain medications may also cause this thickening of the skin as a side effect. Particularly nicotinic acid and birth control pills. In addition, various cancers, most importantly those of the gastrointestinal and genitourinary systems, can have this skin manifestation.
There is no specific testing that needs to be done on the skin changes other then a physical exam by your doctor, but you should be checked for diabetes and other metabolic disorders. Your doctor may want to do more invasive tests looking for cancer. In rare cases, a biopsy may be needed.
No specific treatment is needed. Losing weight and eating healthier may help minimize the appearance of the dark, thick skin, and may also decrease your chances of developing diabetes. If that doesn't work and you are bothered by the skin changes, various creams or medications may lighten and smooth the skin. Dermatologists may also be able to offer procedures like dermabrasion and laser therapy to treat the skin changes.
Treating the medical conditions or obesity that accompany acanthosis nigricans can cause regression of the skin disease and result in a good prognosis. Recognize this condition early, treat obesity to prevent the development of diabetes and other weight-related diseases. Unfortunately when acanthosis nigricans prompts a diagnosis of cancer, it may already be advanced and associated with a poor prognosis overall.