Dermatitis

Nummular dermatitis

Created 2008.

Learning objectives

  • Identify and manage nummular dermatitis

Clinical features

Nummular dermatitis (or eczema) is also known as discoid eczema (or dermatitis). It has two forms:

  • Exudative (‘wet’) nummular dermatitis
  • Dry nummular dermatitis

Exudative nummular dermatitis
The exudative variant starts acutely and may persist for weeks, months and rarely years. Although it may arise at any age, most subjects are over 50 years. In children, it is often thought to be a type of atopic dermatitis, but in adults it doesn't appear to relate to atopy. It is more common in males than females.

The initial plaque may appear at the site of trauma or infection. For example:

  • Thermal burn
  • Scabies infestation
  • Varicose vein surgery
  • Insect bite
  • Impetigo

Nummular dermatitis is sometimes due to drug allergy (e.g. to interferon alpha, intravenous immunoglobulins, etanercept) or systematised contact allergy, especially to nickel, gold and mercury.

The initial lesions are papules or vesicles, which form confluent plaques. The plaques may be crusted, weeping or blistered and are intensely itchy. Secondary infection with pustules, pain and spreading erythema is not uncommon. Older lesions may be dry and excoriated.

Clusters of round or oval plaques may be localised to lower legs, the backs of the hands or other sites. Nummular dermatitis may also generalise to affect scalp, face, trunk and limbs. Generally the eruption is scattered, but sometimes the plaques are distributed symmetrically. In-between skin appears normal.

Exudative nummular dermatitis

Dry discoid eczema
Dry discoid eczema can be localised or generalised. It often arises as the result of dry skin:

  • In atopics
  • Due to excessive soap and water
  • As a complication of oral retinoids
Dry discoid eczema

Sometimes dry discoid eczema is associated with elevated skin lesions such as seborrhoeic keratoses and melanocytic naevi (Meyerson's naevus).

Autosensitisation dermatitis is a variant of discoid dermatitis affecting the trunk and limbs that follows a severe dermatitis in aother site (an ide reaction). The primary site is most often the lower legs due to stasis dermatitis. Autosensitisation dermatitis can be very extensive

Autosensitisation dermatitis

Investigations

Skin swabs frequently culture abundant Staphylococcus aureus from exudative nummular dermatitis and sometimes from dry discoid dermatitis.

Skin scrapings for microscopy and fungal culture may be necessary to rule out tinea corporis.

Differential diagnosis

Discoid eczema is frequently confused with the following skin disorders:

  • Psoriasis (redder, scalier plaques, symmetrical distribution, typical psoriatic sites)
  • Tinea corporis (grouped lesions, scaly or pustular edge)
  • Contact dermatitis (irregular shaped and sized lesions, contact factors)
  • Lichen simplex (lichenified plaques, may co-exist with nummular dermatitis)
  • Stasis dermatitis (lower legs, circumferential, hyperpigmentation, lipodermatosclerosis)

Management

Management of nummular dermatitis involves:

  • Emollient creams and ointments if the skin is dry, and lotions to soothe as often as desired;
  • Topical corticosteroids: mild potency ointments for dry discoid eczema, potent or ultrapotent creams for exudative nummular dermatitis;
  • Oral anti-staphylococcal antibiotics for secondary infection, and as a trial for several weeks for exudative dermatitis; the most useful are flucloxacillin, dicloxacillin, erythromycin and trimethoprim + sulphamethoxazole;
  • In severe cases, apply wet dressings and prescribe oral corticosteroids for 2 to 4 weeks, slowly reducing the dose and discontinuing within another 4-6 weeks;
  • Resistant cases may require intralesional corticosteroid injections, phototherapy and/or immunosuppressive medications.

Activity

Describe the use of oral corticosteroids in the management of nummular dermatitis. What are the contraindications, precautions, side effects and risks of this treatment and how should you manage these?

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Related information

References:

On DermNet NZ:

Information for patients

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