Page 86 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 4-1 Integumentary System

ACANTHOSIS NIGRICANS

Acanthosis nigricans is a commonly encountered skin
dermatosis that can be seen in various clinical scenarios.
It is overwhelmingly associated with obesity but can Velvety hyperpigmented plaques
occur secondary to medications, endocrine disorders and patches in the axilla
such as the HAIR-AN syndrome (hyperandrogenism,
insulin resistance, and acanthosis nigricans), diabetes,
and internal malignancies. This last type is clinically
distinctive and manifests in a unique manner.
Clinical Findings: Classic cases of acanthosis nigri-
cans affect the nape of the neck, the axillae, and the groin
regions. Native Americans and African Americans are at
a significantly increased risk for development of acan-
thosis nigricans. The slow, insidious onset of patches and
plaques with a velvety, hyperpigmented, thickened,
rough surface is characteristic of acanthosis nigricans.
Maceration with a malodorous smell is often noted. The
patients are for the most part asymptomatic, although
some complain of intermittent pruritus. The clinical
findings in association with obesity are enough to make
the diagnosis. A thorough history should be taken to rule
out a medication-induced form of acanthosis nigricans.
The only routine laboratory testing performed is screen-
ing for occult diabetes. Patients with obesity are at higher
risk for diabetes later in life, and lifelong follow-up and
screening by their primary care physician is required.
Many medications have been shown to induce
acanthosis nigricans. They include niacinamide, gluco-
corticoids, insulin, and some birth control pills. The
medication most commonly associated with acanthosis
nigricans is niacinamide. Most cases resolve or improve
greatly with discontinuation of the medication. The
appearance is often identical to that of classic acanthosis
nigricans, but the history is suggestive, with the timing
of rash onset related to the introduction of the causative
medication.
Malignancy-associated acanthosis nigricans is often
widespread and involves unique areas, including the
mucous membranes, palms, and soles. This form has a
rapid onset and affects different areas of the body than
the classic form of acanthosis nigricans does. The palms
and soles are often involved, and the face can be
involved. Any case in which there is rapid onset of
acanthosis nigricans in a widespread distribution, often Acanthosis nigricans. Hyperpigmented plaques on
in a nonobese individual, warrants proper evaluation to the dorsal foot with accentuation of the skin lines
rule out an internal malignancy. Referral to a gastroen-
terologist and an internist for cancer screening is of
utmost importance.
A few endocrine disorders can be associated with
acanthosis nigricans, most frequently diabetes mellitus
and the HAIR-AN syndrome It is associated with
insulin resistance and also with hyperandrogenism.
Rare causes of acanthosis nigricans include the
familial forms, which are inherited in an autosomal
dominant fashion.
Pathogenesis: The skin thickening and clinical find-
ings are possibly caused by an increase in insulin-like
growth factor receptor, fibroblast growth factor recep- medication’s local effects on the skin in genetically which the skin findings of acanthosis nigricans will
tor, and epidermal growth factor receptor and their predisposed individuals. resolve. Temporizing methods of therapy include the
subsequent effects on the skin. The reason it affects Histology: Epidermal hyperplasia, acanthosis, and use of keratolytic agents such as lactic acid to help thin
certain regions preferentially is unknown. Malignancy- papillomatosis are present. There is minimal to no the plaques and make them less noticeable. These
associated acanthosis nigricans is believed to be caused inflammatory infiltrate, and the dermis is essentially agents are difficult to use in the axillae because of sting-
by some cytokine or growth factor directly secreted by normal in appearance. Extensive hyperkeratosis with a ing. The topical use of tretinoin cream has also been
the tumor, possibly in the fibroblast growth factor mild excess of melanin production likely explains the successful. Destructive laser therapies have been used
receptor class of molecules. The tumor causes the clini- hyperpigmentation seen in acanthosis nigricans. with varying success.
cal findings by secreting these substances. Acanthosis Treatment: Treatment is often difficult unless the Treatment of malignancy-associated acanthosis
nigricans is believed to be a paraneoplastic process in afflicted individual makes a conscious effort to get to an nigricans is directed at the underlying malignancy.
these cases. Medication-induced acanthosis nigricans ideal body weight and to get his or her diabetes under Removal of the tumor may result in complete resolu-
is poorly understood but is possibly related to the excellent control. This is the only likely scenario in tion of the skin disease.

72 THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS