Nummular Dermatitis 

  • Author: Jami L Miller, MD; Chief Editor: William D James, MD   more...
 
Updated: May 20, 2011
 

Background

Nummular (meaning "coin-shaped") dermatitis is a form of eczema. Nummular dermatitis is characterized by round-to-oval erythematous plaques most commonly found on the arms and legs. Lesions often start as papules, which then coalesce into plaques with scale. Early nummular dermatitis lesions may be studded with vesicles containing serous exudate. They are usually very pruritic.

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Pathophysiology

Nummular dermatitis is a condition confined to the skin. It has recently been classified as a form of atopic dermatitis.

Little is known about the pathophysiology of nummular dermatitis, but it is frequently accompanied by xerosis. Dryness of the skin results in dysfunction of the epidermal lipid barrier; this may allow permeation of environmental allergens, which induce an allergic or irritant response.[1, 2] This is supported by one study that showed that elderly patients with nummular dermatitis had increased sensitivity to environmental aeroallergens compared with age-matched controls. This impaired cutaneous barrier in the setting of nummular dermatitis may also lead to increased susceptibility to allergic contact dermatitis to materials such as metals.

Onset has been associated with medications. Onset of severe, generalized nummular lesions has been reported in association with interferon and ribavirin therapy for hepatitis C.[3, 4] Association with use of inhibitors of tumor necrosis factor has also been reported.[5]

Onset has also been described in association with mercury in dental amalgams. Hypersensitivity to the metals in the mouth is posulated to be sufficient to drive an immune response that results in cutaneous nummular plaques.

Because of the intense pruritus associated with nummular dermatitis, the potential role of mast cells in the disease process has been investigated. Increased numbers of mast cells have been observed in lesional compared with nonlesional samples in persons with nummular dermatitis.

One study identified neurogenic contributors to inflammation in both nummular dermatitis and atopic dermatitis by investigating the association between mast cells and sensory nerves and identifying the distribution of neuropeptides in the epidermis and upper dermis of patients with nummular eczema. Researchers hypothesized that release of histamine and other inflammatory mediators from mast cells may initiate pruritus by interacting with neural C-fibers. The research showed that dermal contacts between mast cells and nerves were increased in number in both lesional and nonlesional samples of nummular eczema compared with normal controls. In addition, substance P and calcitonin gene-related peptide fibers were prominently increased in lesional samples compared with nonlesional samples from patients with nummular eczema. These neuropeptides may stimulate release of other cytokines and promote inflammation.[6, 7, 8]

Other research has demonstrated that mast cells present in the dermis of patients with nummular eczema may have decreased chymase activity, imparting reduced ability to degrade neuropeptides and protein. This dysregulation could lead to decreased capability of the enzyme to suppress inflammation.

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Epidemiology

Frequency

United States

The prevalence of nummular dermatitis is 2 cases per 1000 people. Dermatitis (eg, atopic, asteatotic, dyshidrotic, nummular, hand) is one of the most common dermatologic conditions.

International

The incidence internationally is the same as it is in the United States.

Mortality/Morbidity

  • Pruritus, often worst at night, may cause irritability, insomnia, or both.
  • Secondary infection may result in lesions that ooze serosanguineous exudate. The most common organism revealed by culture is Staphylococcus aureus.
  • Generalized flares may require bed rest, oral antibiotics, a cool environment, systemic antibiotics, and/or systemic steroids.
  • Increased contact sensitivity to environmental antigens (especially metals) could limit ability to tolerate those antigens, especially clothing, metal snaps, jewelry, dental amalgams or occupational exposure.

Race

No racial predilection has been observed for nummular dermatitis.

Sex

Nummular dermatitis is more common in males than in females (see Age below).

Age

Nummular dermatitis has 2 peaks of age distribution. The most common is in the sixth to seventh decade of life. This is most often seen in males. A smaller peak occurs in the second to third decade of life, which is most often seen in association with atopic dermatitis. This is more often seen in females. It is uncommon in children.

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Contributor Information and Disclosures
Author

Jami L Miller, MD  Assistant Professor, Division of Dermatology, Department of Internal Medicine, Vanderbilt University Medical School; Director of Phototherapy Unit, Vanderbilt University Medical Center; Consulting Attending Physician, Nashville Veterans Affairs Medical Center

Jami L Miller, MD is a member of the following medical societies: American Academy of Dermatology, American College of Physicians, and American Medical Association

Disclosure: Nothing to disclose.

Specialty Editor Board

John D Wilkinson, MD, MBBS, MRCS, FRCP  Chairman, Clinical Director, Department of Dermatology, Amersham Hospital and High Wycombe Hospital, UK

John D Wilkinson, MD, MBBS, MRCS, FRCP is a member of the following medical societies: American Academy of Dermatology and Royal College of Physicians

Disclosure: Nothing to disclose.

Richard P Vinson, MD  Assistant Clinical Professor, Department of Dermatology, Texas Tech University Health Sciences Center, Paul L Foster School of Medicine; Consulting Staff, Mountain View Dermatology, PA

Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Association of Military Dermatologists, Texas Dermatological Society, and Texas Medical Association

Disclosure: Nothing to disclose.

Paul Krusinski, MD  Director of Dermatology, Fletcher Allen Health Care; Professor, Department of Internal Medicine, University of Vermont College of Medicine

Paul Krusinski, MD is a member of the following medical societies: American Academy of Dermatology, American College of Physicians, and Society for Investigative Dermatology

Disclosure: Nothing to disclose.

Catherine M Quirk, MD  Clinical Assistant Professor, Department of Dermatology, University of Pennsylvania

Catherine M Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology

Disclosure: Nothing to disclose.

Chief Editor

William D James, MD  Paul R Gross Professor of Dermatology, University of Pennsylvania School of Medicine; Vice-Chair, Program Director, Department of Dermatology, University of Pennsylvania Health System

William D James, MD is a member of the following medical societies: American Academy of Dermatology and Society for Investigative Dermatology

Disclosure: Elsevier Royalty Other

References

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Dry, scaling plaque of nummular dermatitis (size, 3 X 5 cm) on the shin.
 
 
 
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