Nummular Dermatitis
- Author: Jami L Miller, MD; Chief Editor: William D James, MD
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.
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.[3]
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.[4, 5] Association with use of inhibitors of tumor necrosis factor has also been reported.[6]
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.[7, 8, 9]
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.
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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