Welcome to the Rare Classroom, a new series from Patient Worthy. Rare Classroom is designed for the curious reader who wants to get informed on some of the rarest, most mysterious diseases and conditions. There are thousands of rare diseases out there, but only a very small number of them have viable treatments and regularly make the news. This series is an opportunity to learn the basics about some of the diseases that almost no one hears much about or that we otherwise haven’t been able to report on very often.

Eyes front and ears open. Class is now in session.

The disease that we will be learning about today is:

Acanthosis Nigricans

What is Acanthosis Nigricans?

• Acanthosis nigricans is a condition in which areas of skin develop hyperpigmentation and a velvet-like texture.
  • These areas are often poorly defined, and the skin develops a brownish or blackish coloration.
• The condition tends to in certain areas, such as the navel, forehead, neck, armpits, and groin.
• Acanthosis nigricans is linked to diseases impacting the endocrine system, such as hyperinsulinemia and insulin resistance. These often occur in diabetes.

How Do You Get it?

• Most patients are less than 40 years old.
• Acanthosis nigricans can have several different causes. In fact, there are six different forms, most of which are distinguished by their cause.
  • Type I is inherited in an autosomal dominant fashion. The condition can appear at birth or in childhood.
  • Type II is the result of endocrine syndromes (including rare diseases) such as:
    • Metabolic syndrome, insulin resistance, diabetes, polycystic ovarian disease, Cushing’s disease, acromegaly, hypothyroidism, Addison’s disease, lipoatrophic diabetes, pinealoma, Prader-Willi syndrome, among others
  • Type III is linked to obesity and has no direct cause otherwise, though insulin resistance may be the main factor.
  • Type IV is related to the use of certain drugs, such as growth hormone, nicotinic acid, combined oral contraceptives, and glucocorticoids
  • Type V occurs alongside cancer and is classified as a paraneoplastic syndrome. While it can occur alongside a wide variety of cancers, it is most commonly associated with gastrointestinal adenocarcinomas, ovarian cancer, prostate cancer, and breast cancer.
  • Acral acanthotic anomaly refers to an abnormal form of acanthosis nigricans that appears on the tops of the feet, knuckles, knees, and elbows. These patients are otherwise healthy.
• The mechanism involves an increase in the activation of growth factor receptor proteins, such as insulin-like growth factor receptor, epidermal growth factor receptor, and fibroblast growth factor receptor. This causes a proliferation of cells in the skin such as keratinocytes and fibroblasts.

What Are The Symptoms?

• The defining symptom of acanthosis nigricans is areas of skin that are relatively darker than other areas, increased in thickness, and have a velvety texture.

How Is It Treated?

• People that are diagnosed with acanthosis nigricans should be screened for diabetes or cancer in some cases.
• In mild cases, topical skin creams can normalize skin appearance.
• Lifestyle changes, such as exercise and dietary changes, can also help improve symptoms.
• Selenium sulfide has also been documented as an effective therapy.
• Treatment of the underlying condition (cancer, diabetes, endocrine dysfunction, etc.) can also resolve acanthosis nigricans.

Where Can I Learn More???

• Check out our cornerstone on this disease here.
• Learn more about this condition from the American Academy of Dermatology Association.