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From Medscape Dermatology Clinic

A Dark Rash Involving the Body Folds

Stanford I. Lamberg, MD
[Medscape Dermatology, 2001. © 2001 Medscape, Inc.]

Case Presentation Patient
A 44-year-old white male with a non-itchy, dark rash of 2 months' duration involving the body folds

The patient has no pertinent medical problems, except for elevated cholesterol and triglycerides. He was being treated with niacin (3 g/day), which he had been taking for 5 months.

Physical Exam
The skin around the neck, axillae, and groin was thickened, dark brown-black, with a velvety surface.

Laboratory Data and Histopathology
None were obtained.

What is your diagnosis?
A. Pellagra

B. Acanthosis nigricans

C. Contact dermatitis

D. Addison's disease

The answer was Acanthosis nigricans.

Discussion of Answer
Pellagra is characterized by a scaly dermatitis with dusky brown pigmentation, and it appears on sun-exposed areas. It results from a deficiency of nicotinic acid, niacin, or its precursor, tryptophan.

Chronic contact dermatitis in the axillae may lead to thickening of the skin and hyperpigmentation, but chronic itching typically accompanies this eruption.

Addison's disease also may present with hyperpigmentation. The pigmentation is darkest on sun-exposed areas, although body folds may be involved. Those affected usually are weak, thin, and gaunt.

Acanthosis nigricans is asymptomatic, brown to black, with a velvety texture. Pedunculated skin tags often are present. The most common sites are the axillae, neck, and groin. If the patient is obese, the eruption may clear with weight loss or correction of the underlying endocrine disorder. Local treatment is not effective.

Acanthosis nigricans usually is classified into 2 types: a benign form, not associated with malignancy, and a malignant form. Patients with the malignant form of acanthosis nigricans tend to be thin and older than 40 years of age, and their eruption is of recent origin. The most common malignancy associated with malignant acanthosis nigricans is abdominal adenocarcinoma, especially of the stomach.

Most patients with the benign form are obese. Some have an endocrinopathy, such as diabetes mellitus, especially of the insulin-resistant type; pituitary or adrenal adenomas; Cushing's syndrome; intake of stilbestrol; or the Stein-Leventhal syndrome (polycystic ovary disease). Other causes include chronic hepatitis and ingestion of large doses of niacin.

Niacin (nicotinic acid) remains a useful drug for hypertriglyceridemia because its use reduces both triglycerides and LDL cholesterol, while it raises HDL cholesterol. However, it worsens control of blood sugar in diabetes mellitus and often produces unpleasant side effects, including cutaneous flushing, pruritus, and gastrointestinal distress due to histamine release. Additional adverse effects include occasional elevated uric acid and liver enzymes, as well as the uncommon side effect of acanthosis nigricans reviewed here.

Niacin was discontinued and replaced with a different lipid-reducing medication. The eruption slowly cleared over the next several months.

• Hud JA Jr, Cohen JB, Wagner JM. Prevalence and significance of acanthosis nigricans in an adult obese population. Arch Dermatol. 1992;128:941-944.
Kurzrock R, Cohen PR. Cutaneous paraneoplastic syndromes in solid tumors. Am J Med. 1995;99:662-671.
• Schwartz RA. Acanthosis nigricans. J Am Acad Dermatol. 1994;31:1-19.
• Stals H, Vercammen C, Peeters C, Morren M. Acanthosis nigricans caused by nicotinic acid: case report and review of the literature. Dermatology. 1994;189:203-206.

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