Nummular eczema is a non-infectious condition characterized by round or oval, raised, reddened and often intensely itchy patches on your skin. These lesions typically begin as groups of small bumps or blisters on your arms or legs that eventually coalesce to form coin-shaped plaques. The central portions of older lesions often clear, producing patches that are similar in appearance to ringworm, a fungal infection. Nummular eczema can be resistant to treatment, and it tends to recur. Lesions that are traumatized by scratching or that become infected are more likely to form scars after healing.
Causes and Associations
The cause of nummular eczema is unknown, but it occurs more frequently in people with allergies, pointing to a possible allergic mechanism. Nummular eczema is not contagious. It occurs more commonly if your skin is excessively dry, during the winter and following exposure to environmental irritants, such as wool, lanolin, cosmetics, metals or preservatives. Individual lesions can persist for many weeks despite aggressive treatment, and recurrence – often in the same location as prior eruptions – is the norm. The lesions of nummular eczema usually heal without scarring, but complications can occur.
Post-inflammatory Hyperpigmentation
Nummular eczema is very similar to a condition called atopic, or allergic, dermatitis. The chronic inflammation seen in both conditions involves immune cells that secrete inflammatory chemicals and free radicals into your skin. These substances damage the melanocytes, or pigment-producing cells, in the deeper layers of your skin, provoking the release of melanin, which is subsequently taken up by maintenance cells that can remain in one location for many months or even years. Thus, healing nummular eczema can leave dark splotches in your skin that can, in some cases, be permanent. This tends to be more troublesome in people with darker skin, and it is more likely to occur on your lower legs.
Corticosteroid Complications
Since nummular eczema causes significant discomfort for most patients and is typically slow to resolve, dermatologists frequently prescribe potent medications to reduce your symptoms and to speed healing. Coal tar, corticosteroids and immune-modulating agents are among the most useful topical preparations for nummular eczema. Unfortunately, the long-term use of high-potency, topical corticosteroids can lead to spider veins, stretch marks and localized skin atrophy, which appears as a hollowing or dimpling caused by loss of subcutaneous fat. Like post-inflammatory hyperpigmentation, some of these changes can be permanent.
Scars Can Be Prevented
Nummular eczema can take many weeks to heal, even with effective treatment. Scarring due to nummular eczema can be limited by avoiding trauma, which is usually caused by scratching, and by promptly treating secondary bacterial infections with antibiotics. Aggressive treatment of nummular eczema usually minimizes hyperpigmentation, and judicious use of topical corticosteroids helps to prevent atrophy, striae and spider vein formation. If you have nummular eczema, you probably have an ongoing relationship with a dermatologist who is the best source of information for treating this disorder and preventing its complications.
References
- “California and Western Medicine”; Nummular Eczema; E. D. Chipman; May 1934
- MedlinePlus: Nummular Eczema
- “Indian Journal of Dermatology, Venereology, and Leprology"; Relevance of Patch Testing in Patients With Nummular Dermatitis; D.S.K. Shankar; Nov-Dec 2005
- “The Journal of Clinical and Aesthetic Dermatology”; Postinflammatory Hyperpigmentation: A Review of the Epidemiology, Clinical Features, and Treatment Options in Skin of Color; E. C. Davis, et al.; July 2010
- “American Family Physician”; Choosing Topical Corticosteroids; J. D. Ference, et al.; January 2009
