Discoid eczema

Discoid eczema, also known as nummular dermatitis, is a common type of dermatitis. It can occur at any age and affects males and females equally.

What is the cause of discoid eczema?

The cause of discoid eczema is unknown. There are dry and wet types.

In most cases, discoid eczema does not run in families. It does not result from food allergy. It is not infectious to other people, although it sometimes becomes secondarily infected by bacteria.

• Minor skin injury such as an insect bite or a burn may start it off.
• In some children, it is a manifestation of atopic dermatitis.
• Autoeczematisation or id reactions can present as discoid eczema.
• It may be termed ‘varicose eczema’ when it runs along the leg veins or may complicate gravitational eczema.
• Dry skin in the winter months can cause dry non-itchy round patches.
• The wet type presents as crusted or blistered patches.

What does it look like?

Discoid eczema can affect any part of the body particularly the lower leg. One or many patches appear, and may persist for weeks or months.

The majority of patches are round or oval, hence the name ‘discoid‘ or ‘nummular’ dermatitis, which refers to their disc or coin shape. They can be several centimetres across, or as small as two millimetres.

The patches are pink, red, or brown and well defined. They have a dry cracked surface or a bumpy, blistered or crusted surface. Discoid eczema may be extremely itchy, or scarcely noticeable. 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).

Nummular dermatitis

More images of nummular dermatitis ...

Investigations

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.

Treatment

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.

Emollients
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: aqueous cream, glycerine & cetomacrogol cream, white soft paraffin/liquid paraffin mixed, wool fat lotions.

Topical steroids
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 about 15 days. They are repeated from time to time. Mild ones such as hydrocortisone are safe for daily use if necessary.

Oral or topical antibiotics
Antibiotics (most often flucloxacillin) are important if the dermatitis is weeping, sticky or crusted. Sometimes nummular dermatitis clears completely on oral antibiotics, only to recur when they are discontinued.

Oral antihistamines
Antihistamine pills may reduce the itching, and are particularly helpful at night-time. They do not clear the dermatitis. Newer non-sedating antihistamines appear less useful for this condition, possibly because part of the effect of the conventional type is due to making the person sleepy.

Phototherapy
Ultraviolet light treatment several times weekly can help. It may take several months to control the eczema but is worthwhile for more severe cases.

Systemic steroids
Steroids by mouth or injection are reserved for severe and extensive cases of nummular dermatitis. Systemic steroids are usually only necessary for a few weeks, and any residual dermatitis can be treated satisfactorily with steroid creams and emollients.

Nummular dermatitis can usually be controlled with the above measures, although it has a tendency to recur when the treatment has been stopped. Make sure the skin is kept well moisturised, and protected from injury. Eventually, the dermatitis clears up completely.