What is discoid eczema?
Discoid eczema, also known as nummular dermatitis, is a common type of eczema / dermatitis, in which there are round or oval, blistered or dry, skin lesions.
What is the cause of discoid eczema?
The cause of discoid eczema is unknown. Some cases are associated with Staphylococcus aureus infection.
The eruption can be precipitated by:
- Localised injury such as scratch, insect bite or thermal burn
- Impetigo or wound infection
- Contact dermatitis
- Dry skin
- Varicose veins (varicose eczema)
- Other skin problem
Who gets discoid eczema?
Discoid eczema can affect children and adults. It is slightly more prevalent in adult males than females. In males over the age of 50 years, there is an association with chronic alcoholism.
What are the clinical features of discoid eczema?
There are two forms of discoid eczema:
- Exudative acute discoid eczema: oozy papules and plaques
- Dry discoid eczema: subacute or chronic erythematous, dry plaques
Both forms of discoid eczema are usually more prevalent on the limbs than the trunk, but the rash may be widespread. Although often bilateral, the distribution is often asymmetrical.
Individual plaques are well-demarcated, mostly 1–3 cm in diameter, and inflamed. The majority of patches are round or oval, hence the name ‘discoid‘ or ‘nummular’ (coin shape). The plaques are usually very itchy but sometimes don't itch at all. The skin between the patches is usually normal, but may be dry and irritable.
Severe discoid eczema may generalise, with numerous small to large itchy lesions appearing all over the body due to autoeczematisation reaction.
The patches may clear up without leaving a sign. However, in darker skins, marks may persist for months. These may be dark brown (postinflammatory hyperpigmentation) or paler than surrounding skin (postinflammatory hypopigmentation).
More images of Discoid eczema ...
What tests should be done?
In most cases, no investigations are necessary as the appearance of discoid eczema is quite characteristic. Bacterial swabs may reveal Staphylococcus aureus colonisation or infection. Scrapings are commonly taken for mycology, as discoid eczema can look very similar to tinea corporis (ringworm infection).
Sometimes patch testing is arranged to see whether there could be a contact allergy responsible for the dermatitis. In most cases no specific allergy can be found.
What is the treatment of discoid eczema?
As discoid eczema is associated with loss of skin barrier function, it is important to:
Protect the skin from injury.
As this type of dermatitis often starts off as minor skin injuries, protect all your skin carefully. If the hands are affected, use gloves and tools to make sure the skin is not irritated by friction, detergents, solvents, other chemicals or excessive water.
Apply emollients frequently
Emollients include bath oils, soap substitutes and moisturizing creams. They can be applied to the dermatitis as frequently as required to relieve itching, scaling and dryness. Emollients should also be used on the unaffected skin to reduce dryness. It may be necessary to try several different products to find one that suits. Many people find one or more of the following helpful: sorbolene, glycerine & cetomacrogol cream, white soft paraffin/liquid paraffin mixed, fatty cream, wool fat lotions.
Anti-inflammatory treatments include:
Topical steroids are anti-inflammatory creams or ointments available on prescription which may clear the dermatitis and reduce irritation. The stronger products are applied to the patches just once or twice daily for 2–4 weeks. They are repeated from time to time. Mild ones such as hydrocortisone are safe for daily use if necessary.
Antibiotics (most often flucloxacillin) are often prescribed if the dermatitis is blistered, sticky or crusted. Sometimes discoid eczema clears completely on oral antibiotics, only to recur when they are discontinued.
Other treatments sometimes prescribed for severe discoid eczema include:
Antihistamine pills may reduce the itching, and are particularly helpful at night-time. They do not clear the dermatitis. Non-sedating antihistamines appear less useful for discoid eczema than first-generation antihistamines taken at night to help sleep.
Ultraviolet radiation (UV) treatment
Phototherapy several times weekly for 6–12 weeks can reduce extent and severity of discoid eczema.
Intralesional steroids are sometimes injected into one or two particularly stubborn areas of discoid eczema. This treatment is unsuitable for multiple lesions.
Systemic steroids are reserved for severe and extensive cases of discoid eczema. They are usually prescribed for a few weeks, while continuing steroid creams and emollients on residual dermatitis.
Other oral treatments
Persistent and troublesome discoid eczema is occasionally treated with methotrexate, azathioprine or ciclosporin. These medicines have important risks and side effects and require careful monitoring by a specialist dermatologist. They may be more suitable in many cases than long-term s steroids.
Discoid eczema can usually be controlled with the above measures, although it has a tendency to recur when the treatment has been stopped. In most patients the dermatitis eventually clears up completely.
On DermNet NZ:
- Atopic dermatitis
- Patch testing
- Topical steroids
- Systemic steroids
- Dermatitis online course for health professionals
Books about skin diseases:
See the DermNet NZ bookstore