Background
Nummular (ie, round or coin-shaped) dermatitis (nummular eczema) is an inflammatory skin condition characterized by the presence of well-demarcated round-to-oval erythematous plaques. Since its first description by Deverigie in 1857, it has been reported in all age groups and in all body areas, but it is most commonly found on the upper and lower extremities. [1]
The term nummular dermatitis has been used both as a label for an independent disease and as a description of lesion morphology that can be found in many different diseases, including atopic dermatitis, contact dermatitis, and asteatotic eczema. This discussion focuses on the independent disease entity described in the literature. Other names that have been used for this condition include diskoid eczema and orbicular eczema.
Signs and symptoms
The lesions most often start as papules, which coalesce into plaques; they are usually scaly. Early lesions may be studded with vesicles containing serous exudate. Nummular eczema usually is highly pruritic. Many precipitating factors have been reported, including dry skin, contact allergies, weather (particularly winter), nutritional issues, and emotional stress.
Workup
Tinea corporis should be excluded by scraping and microscopically analyzing a potassium hydroxide preparation of a lesion.
For lesions that have erythema spreading away from the lesions, suggesting cellulitis, swab culture of the exudate may be helpful. First-generation cephalosporins are still usually effective first-line treatment. As methicillin-resistant Staphylococcus aureus (MRSA) becomes more common in a community, the culture results help in the choice of appropriate antibiotic therapy for treatment-resistant cases of documented secondarily infected lesions.
If the history is suggestive of infection, a workup for infection (eg, with Helicobacter pylori or Giardia) should be considered.
Management
Treatment includes moisturizers and topical steroids. If there is an overt infection, a combination of a topical antibiotic and a steroid ointment may be used. Nighttime use of antihistamines can help with sleep. Severe or generalized flares may be treated with dressings on top of the steroid ointment. Oral or parenteral steroids may be used in severe flares, followed by topical therapy. Oral antibiotics, such as dicloxacillin, cephalexin, or erythromycin, should be used in cases of secondary infection.
Pathophysiology
Little is known about the pathophysiology of nummular eczema, but as with most other forms of dermatitis, the cause is likely to be a combination of epidermal lipid barrier dysfunction and an immunologic response.
Nummular eczema is known to be frequently accompanied or preceded by xerosis. Dryness of the skin results in "leaking" of the epidermal lipid barrier; this allows environmental allergens and bacteria to penetrate the skin and induce an allergic or irritant immune response. [2] A study by Aoyama et al showed that elderly patients with nummular dermatitis were more sensitive to environmental aeroallergens than age-matched control subjects were. [3] This impaired cutaneous barrier in the setting of nummular eczema may also lead to increased susceptibility to allergic contact dermatitis to materials such as metals, soaps, and chemicals. [1]
Nummular eczema has been associated with medications. Theoretically, it can be initiated by any medication that induces dryness of the skin, particularly diuretics and statins. the onset of severe, generalized nummular lesions has been reported in association with interferon and ribavirin therapy for hepatitis C. [4, 5] Other medications that influence immune response may also induce nummular eczema, including tumor necrosis factor (TNF) inhibitors [6] and guselkumab. [7]
Nummular eczema can occur after surgery. A review of 1662 Japanese women found that nummular eczema developed in almost 3% of patients undergoing breast reconstruction, presumably due to surgical cleansers or bandage tape. [8] Kost et al reported two cases of nummular eczema developing as a postoperative complication of total knee arthroplasty in elderly women. [9]
The onset of nummular dermatitis 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 eczema, the potential role of mast cells in the disease process has been investigated. Increased numbers of mast cells have been observed in lesional samples as compared with nonlesional samples in persons with nummular dermatitis.
One study identified neurogenic contributors to inflammation in both nummular eczema 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. [10] Researchers hypothesized that release of histamine and other inflammatory mediators from mast cells might initiate pruritus by interacting with neural C-fibers. The number of dermal contacts between mast cells and nerves was increased in both lesional and nonlesional samples from patients with nummular eczema as compared with normal control subjects.
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. [10] These neuropeptides may stimulate release of other cytokines and promote inflammation.
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. [11] This dysregulation could lead to decreased capability of the enzyme to suppress inflammation.
Colonization of the skin with S aureus has been described both on lesional skin and in the nares of patients and their close contacts. [12] Whether this is important in the precipitation of disease remains to be determined.
Etiology
The etiology of nummular eczema is unknown and likely multifactorial. Most patients with nummular eczema also have very dry (xerotic) skin. Local trauma (eg, from arthropod bites, contact with chemicals, or abrasions) may precede an outbreak.
Contact dermatitis may play a role in some cases. Contact dermatitis may be irritant or allergic in nature. Sensitivity to nickel, cobalt, or chromates has been reported in patients with nummular dermatitis. In one study, the most frequent sensitizers were colophony, nitrofurazone, neomycin sulfate, and nickel sulfate. In the past, cases of nummular eczema–like eruptions have been caused by ethyl cyanoacrylate–containing glue, thimerosal, mercury-containing dental amalgams, [13] and depilating creams containing potassium thioglycolate. [14]
Venous insufficiency (and varicosities), stasis dermatitis, and edema may be related to the development of nummular eczema on the affected lower extremities.
Autoeczematization (ie, lesional spread from the initial focal site) may account for the presence of multiple plaques.
The onset of severe, generalized nummular lesions has been reported in association with interferon therapy for hepatitis C, as well as exposure to mercury. [4, 5] Various types of eczematous eruptions, including nummular eczema, have been observed following TNF-α–blocking therapy, [6] and nummular dermatitis has also been reported after treatment of psoriasis with guselkumab. [15]
Nummular eczema of the breast has reported in breast cancer patients undergoing mastectomy with subsequent breast reconstruction. [16, 17] In the majority of these patients, this condition developed after the insertion of tissue expanders or breast implants, which suggested that stretching of the skin might play a role in causing it.
In rare cases, nummular eczema has been found in association with infection. It has been reported as a manifestation of giardiasis. [18] In a study that included patients with H pylori infection and nummular eczema, eradication of H pylori led to clearance of the skin lesions in 54% of cases. [19] A case report by Tanaka et al described nummular eczema occurring in association with a dental infection that cleared after the treatment of the infection. [20]
In children, nummular eczema occurs most frequency in association with atopic dermatitis. [21]
Epidemiology
The prevalence of nummular eczema is two cases per 1000 people. Dermatitis in general (eg, atopic, asteatotic, dyshidrotic, nummular, hand) is one of the most common of dermatologic conditions.
Nummular eczema has two peaks of age distribution. The larger peak is in the sixth and seventh decades of life, more often involving males. A smaller peak is in the second and third decades, usually in association with atopic dermatitis and more often involving females (by two thirds, in one study). [22] Although nummular eczema can also occur in children, this is uncommon. [23]
Overall, nummular eczema is more common in males than in females.
No racial predilection has been established; however, in children, nummular dermatitis appears to be more common in those with skin of color. [21]
Prognosis
Nummular eczema tends to be a chronic condition that remits and relapses.
Pruritus, often worst at night, may cause irritability, insomnia, or both. Secondary infection may result in lesions that ooze serosanguineous exudate; the organism most commonly revealed by culture is S aureus. Generalized flares may require treatment with systemic antibiotics, systemic steroids, or both.
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.
Patient Education
Patients should be informed that once nummular eczema develops, it is often recurrent. Avoidance of exacerbating factors and close attention to moisturizing the skin may help reduce the frequency of recurrences.
Patients must be educated about the most important predisposing condition to nummular eczema: dry skin. Use of gentle soaps and copious application of moisturizers, especially while the skin is still damp after bathing, is imperative. Once the lesions develop, use of topical steroids or calcineurin inhibitors helps with the itch and hastens resolution.
For patient education resources, visit the Skin Conditions and Beauty Center. Also, see the patient education article Eczema.
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Dry, scaling plaque of nummular dermatitis (size, 3 X 5 cm) on shin.
