Acanthosis Nigricans

Dr. Apratim GoelMBBS,MD,DNB

March 23, 2020

March 23, 2020

Acanthosis Nigricans
Acanthosis Nigricans

Acanthosis nigricans is a skin condition marked by hyperpigmentation - seen as dark patches - and a velvet-like thickening of the skin, especially in the skin fold regions like the neck, groin and under the arms. 

The symptoms appear as dark spots, thick velvet-like skin, bad odour, itching and skin tags. The symptoms can also be seen in the mucous membrane of the mouth and nose.

The cause of acanthosis nigricans can be a genetic disposition, obesity, diabetes, hyperinsulinemia, medications, autoimmune disease and rarely cancer.

The treatment of this condition focuses on the treatment of the underlying cause and also lightening the pigmented skin.

Acanthosis nigricans types

There are various types of acanthosis nigricans that affect the human body:

  • Obesity-associated acanthosis nigricans: It is one of the most common types of acanthosis nigricans and is seen in obese people. In many of these patients, the obesity is usually due to insulin resistance. Insulin is a hormone that maintains blood sugar levels in the body.
  • Syndromic acanthosis nigricans: This type is seen in people who are suffering from a syndrome such as Crouzon’s syndrome, Cushing’s syndrome, or polycystic ovary syndrome (PCOS)
  • Benign acanthosis nigricans: This type is also known as an acral acanthotic anomaly, where acral stands for peripheral body parts. Its symptoms are limited to the elbows, knees, knuckles, and dorsal surfaces of the feet.
  • Drug-induced acanthosis nigricans: This type is seen in people who take various medications like nicotinic acid, corticosteroids, contraceptive pill, growth hormone therapy, estrogen, and injectable insulin.
  • Hereditary benign acanthosis nigricans: This type is genetically acquired by people and can be seen at any stage of life.
  • Malignant acanthosis nigricans: This type can be a sign of an underlying malignant (cancerous) condition. Around 90% of malignant acanthosis nigricans cases indicate underlying stomach cancer.
  • Autoimmune acanthosis nigricans: This type is seen in people with autoimmune diseases like systemic lupus erythematosus, Hashimoto’s thyroiditis or Sjogren’s syndrome.
  • Unilateral acanthosis nigricans: This type is also known as nevoid acanthosis nigricans and presents symptoms unilaterally; that is, only on one side of the body. The symptoms can manifest at any stage of life.
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Acanthosis nigricans symptoms

The symptoms of acanthosis nigricans are: 

  • Dark pigmentation of the skin
  • Pigmentation is mostly seen in the skin folds like underarms, neck, elbows, knees, under the breasts and groin area.
  • Thick blackish-brown velvety-textured patches on the skin 
  • Presence of skin tags in and around the dark area
  • Itching in the affected area
  • Bad skin odour 
  • Papillomatosis (finger-like projections) in the affected mucous membrane

Why acanthosis nigricans causes dark spots in different parts of the body

The reasons for the appearance of dark spots on different parts of the body in acanthosis nigricans are:

  • Genetically acquired: Some people may get this velvety patchy skin due to faulty collagen production as there is a defect in fibroblast growth factor. Fibroblasts are cells that resposible for the production of collagen in the body among other functions. Collagen is the most abundant protein in the body that is present in our bones, tissues, skin, hair, everywhere.
  • Hyperinsulinemia: It is a condition marked by high levels of insulin in the blood which activate the insulin-like growth factor (IGF). Activated IGF increases the growth of keratinocytes and dermal fibroblasts which lead to the development of velvety skin.
  • Insulin resistance: People who have insulin resistance have a high amount of insulin in their blood. This activates IGF and eventually leads to the development of velvet-like thick skin. Insulin resistance usually leads to diabetes.
  • Medications: People who take nicotinic acid, corticosteroids, contraceptives, growth hormone therapy, estrogen therapy, and injectable insulins may present with dark spots on the body.
  • Autoimmune disease: Autoimmune diseases like systemic lupus erythematosus (SLE), scleroderma, Hashimoto’s thyroiditis or Sjogren’s syndrome may develop acanthosis nigricans.
  • Cancer: It is quite rare, but these dark spots can also be a sign of cancers like stomach cancer, breast cancer, tongue cancer and ovarian cancer.

Acanthosis nigricans diagnosis

Acanthosis nigricans can be diagnosed easily by a dermatologist while doing a skin examination.

Since the treatment is linked to the underlying cause, your doctor may recommend tests such as:

  • Blood tests to test the level of insulin in the blood.
  • Antinuclear antibody test (ANA), in case your doctor suspects an autoimmune disease.
  • You should also tell your dermatologist about any medicines you are taking. These could be for conditions like malabsorption syndrome, arthritis, hormonal imbalance or any inflammation. This will help your doctor to determine if your acanthosis nigricans may be linked to certain medicines.
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Treatment of acanthosis nigricans

The treatment of acanthosis nigricans involves the treatment of underlying conditions along with lightening the pigmentation. The treatment involves the following measures:

  • Treatment of diabetes and hyperinsulinemia to control the insulin levels of the body with the help of a balanced diet and medications.
  • Obese people should try to lose weight.
  • Cancer can be treated by tumour excision which is followed by chemotherapy or radiotherapy.
  • The pigmentation stops as soon as the offending medicines in drug-induced acanthosis nigricans are discontinued.
  • To lighten the skin, retinoid rich creams, ointments and gels may be prescribed by the dermatologists.
  • Laser treatments may be given to reduce the thickness of the skin.
  • Antibiotics and antibacterial soaps are given to reduce the bad odour.