What are the other Names for this Condition? (Also known as/Synonyms)

• Acral Acanthotic Anomaly
• Acral AN
• Benign Acanthosis Nigricans

What is Acral Acanthosis Nigricans? (Definition/Background Information)

• Acanthosis Nigricans (AN) is a skin condition that causes thick, velvety, and darkened skin areas (due to increased thickness of epidermis). It commonly affects the skin of the armpits, the groin region, head and neck (back of the neck), and anal/genital region.
• Acanthosis Nigricans is not contagious and it cannot be transmitted from one individual to another. But, it is associated with many disorders, such as obesity, diabetes, and malignancy
• Acral (indicating peripheral body parts) Acanthosis Nigricans is one among the 7 types of Acanthosis Nigricans. It is different from the other types of Acanthosis Nigricans in that the lesions are present on the skin overlying the ankle, knee, fingers, and toes
• It has to be noted that generally other Acanthosis Nigricans subtypes more commonly involve the flexures (such as the armpits, groin region), head, and back of the neck regions
• Acral Acanthosis Nigricans affect individuals who are usually healthy and have no associated diseases/conditions, unlike other forms of AN that is seen in association with an underlying condition
• Acral Acanthosis Nigricans is usually diagnosed by a thorough clinical history and physical examination. Even though it is a benign condition, dermatologist consultation and testing is necessary to rule out other causes of the condition
• There is no definitive treatment for Acral Acanthosis Nigricans. However, certain treatment modalities may be used for cosmetic reasons. The prognosis is typically good with no known major complications being noted

Who gets Acral Acanthosis Nigricans? (Age and Sex Distribution)

• Individuals of any age group can be affected by Acral Acanthosis Nigricans, but it is most commonly seen in adult population
• Both males and females of all races and ethnicities can be affected
• However, it more commonly affects individuals of darker skin tones. Thus, people of African origin are affected more than other populations

What are the Risk Factors for Acral Acanthosis Nigricans? (Predisposing Factors)

Following are the known risk factors of Acral Acanthosis Nigricans:

• Individuals with darker skin tones or individuals of African origin have a higher risk
• It usually affects healthy individuals compared to other types for unknown reasons

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one's chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Acral Acanthosis Nigricans? (Etiology)

• Acral Acanthosis Nigricans commonly affects individuals with darker skin tones (of African origin) without any apparent precipitating factors
• Other factors may play a role with respect to other types of Acanthosis Nigricans, such as insulin resistance, cancer, medications, etc.
• Insulin resistance results when the activity of insulin hormone is impaired at the site of its action. Because of insulin resistance, the body secretes more insulin (a condition termed as hyperinsulinemia) as a compensatory mechanism which causes thickening of the epidermis (skin)
• Some scientists also believe that these individuals may have antibodies to the insulin receptor, which causes the insulin resistance

What are the Signs and Symptoms of Acral Acanthosis Nigricans?

The signs and symptoms of Acral Acanthosis Nigricans may include:

• It most commonly presents as hyperpigmented, velvety, poorly-defined skin lesions
• The lesions are limited to the top portion of the feet, elbows, knuckles, and knees (upper and lower extremities)
• The hyperpigmentation can be either brown or black
• The affected individuals are usually healthy

How is Acral Acanthosis Nigricans Diagnosed?

The following procedures may be used to diagnose Acral Acanthosis Nigricans:

• Thorough evaluation of the individual’s medical history and a complete physical examination
• During history-taking, the physicians may enquire about the following:
  • When the symptoms began and whether they are becoming worse
  • List of prescription and over-the-counter medications currently being taken
  • About one’s personal and family history of cancer, diabetes, thyroid abnormalities, ovarian and adrenal gland problems, etc.
• Dermoscopy: It is a diagnostic tool where a dermatologist examines the skin using a special magnified lens
• Wood’s lamp examination: In this procedure, the healthcare provider examines the skin using ultraviolet light. It is performed to examine the change in skin pigmentation
• Various tests and imaging studies to rule out any syndrome/condition that may be associated (or suspected) with AN. This may include cancer, diabetes, obesity, etc.
• A skin biopsy (of the affected skin area) is performed and sent to a laboratory for a pathological examination, who examines the biopsy under a microscope. After putting together clinical findings, special studies on tissues (if needed) and with microscope findings, the pathologist arrives at a definitive diagnosis

Note: A skin biopsy is only rarely performed, when the diagnosis is questionable, or if it resembles other similar skin conditions.

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Acral Acanthosis Nigricans?

The skin lesions of Acral Acanthosis Nigricans generally do not cause any medically-related problems, but it can result in low self-esteem due to cosmetic concerns.

How is Acral Acanthosis Nigricans Treated?

The treatment measures for Acral Acanthosis Nigricans include:

• The treatment of the condition depends upon the underlying cause
• Topical retinoid, bleaching cream, dermabrasion therapy, and long-pulsed alexandrite laser skin therapy are used for addressing the cosmetic issues only. However, they are not a definitive treatment for Acanthosis Nigricans

How can Acral Acanthosis Nigricans be Prevented?

Currently, Acral Acanthosis Nigricans is a condition that has no preventative measures.

What is the Prognosis of Acral Acanthosis Nigricans? (Outcomes/Resolutions)

• In general, Acanthosis Nigricans is a skin sign, which in itself is benign. Thus, the prognosis of Acanthosis Nigricans is excellent with adequate (skin) treatment. However, the overall prognosis depends upon the underlying cause of the condition
• The prognosis of Acral Acanthosis Nigricans is excellent with no associated major complications being noted

Additional and Relevant Useful Information for Acral Acanthosis Nigricans:

• When the biopsied skin tissue is seen by a pathologist under the microscope, the lesions may demonstrate a benign epidermis with hyperkeratosis, papillomatosis, thickening of epidermis (Acanthosis), hyperkeratosis, increased number of melanocytes (melanocytic hyperplasia), and lymphocytic inflammation
• Interestingly, there are only fewer acanthosis with no hyperpigmentation that do not fit the histologic terminology. The hyperpigmented appearance is actually due to hyperkeratosis
• Microscopically, all the 7 types of Acanthosis Nigricans share similar features