Nummular dermatitis is a chronic recurring rash that seems to occur more frequently during the drier, colder months. The lesions usually appear as round or oval-shaped plaques or patches of very dry skin.
Nummular dermatitis usually starts as small papules (bumps) or vesicles (small blisters) that become eroded and crusted. The affected skin is often very itchy and there is sometimes a burning sensation. Areas most commonly involved include the lower legs, buttocks, forearms and the backs of the hands.
This type of eczema is often seen in older individuals. Similar looking round patches of dermatitis may be seen in children with atopic dermatitis.
Although the cause is unknown, minor skin injury, prolonged water exposure or stress may cause this condition to flare. Sensitivity reactions to cobalt, chromates or cobalt can be contributing factors. Flares of nummular dermatitis can also be attributed to a drug allergy.
Other conditions that can resemble nummular dermatitis include psoriasis, tinea corporis and parapsoriasis (although this is usually not itchy). . Skin conditions with superficial similarities include impetigo, Bowen's disease and mycosis fungoides.
If the diagnosis is in doubt, a KOH preparation (potassium hydroxide test to determine fungal infections), bacterial swabs or biopsy may be required. Patch testing may also be useful. In some cases where a contact dermatitis can be identified, clearing can be achieved by avoidance of the allergen.
It is important to reduce contact with irritants. During flares, tap water compressing can sometimes have a drying effect on lesions that are weepy or if pus is present. The mainstay of therapy is the use of mid to high potency topical corticosteroid ointments. Occasionally, tar creams or ointments such as 10% liquor carbonis detergens (LCD) in hydrophilic petrolatum can be utilized.
Oral antibiotics are sometimes required when there is a secondary infection. In very stubborn or severe cases, narrow-band ultraviolet B (UVB) phototherapy, psoralen combined with ultraviolet A (PUVA), oral prednisone, or cyclosporine may be used.
Incorporating emollient-based moisturizers and cleansers as part of daily routine skin care is essential for successfully managing eczema. A persistent feature of eczema is dry skin that is caused by a combination of genetic and environmental factors. Some medical treatments for eczema can further worsen existing dryness, itching, and irritation.
Mild cleansers not only remove impurities and prepare the skin to receive medication, but are unlikely to disrupt the delicate balance of the skin barrier. In addition, treatment of the skin with moisturizers can repair the skin barrier by covering fissures and providing a protective film to reduce the penetrability of microbes, allergens and irritants, and inhibit water loss.
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