Disseminated secondary eczema

What is disseminated secondary eczema?

Disseminated secondary eczema is an acute, generalised eczema/dermatitis that arises in response to a prior localised inflammatory skin disease.

It is also called an id reaction, autosensitisation dermatitis and autoeczematisation.

What causes disseminated secondary eczema?

The cause of disseminated secondary eczema is unknown. Theories have suggested it is an immune response to some component of the skin and/or to circulating infectious agents or cytokines (messenger proteins).

Who gets disseminated secondary eczema?

Disseminated secondary eczema can occur in children and adults, but is more often diagnosed in the elderly with a neglected primary rash on the lower leg.

The most common types of eczema / dermatitis that precede disseminated secondary eczema—an eczematid—are:

• Chronic venous eczema
• Acute contact eczema
• Acute or chronic discoid eczema

Infections preceding disseminated secondary eczema include:

• Fungal infection, eg inflammatory tinea pedis or animal kerion—a dermatophytide
• Bacterial infection, eg wound infection or thermal burn—a bacterid
• Viral infection, eg molluscum contagiosum
• Arthropod infestation eg scabies or lice —a pediculid

What are the clinical features of disseminated secondary eczema?

Disseminated secondary eczema presents as an acute, symmetrical, generalised acute eczema. It tends to be extremely itchy, disturbing sleep.

• Forearms, lower legs, thighs and trunk are commonly affected.
• Appearance varies and includes blisters, bumps, crusted plaques (discoid eczema), follicular papules, morbilliform eruption, targetoid lesions and pompholyx (blisters on palms and soles).
• Occasionally, the patient may feel unwell with fever and loss of appetite.

Non-eczematous id reactions include erythema nodosum, Sweet syndrome, guttate psoriasis and blistering diseases.

How is disseminated secondary eczema diagnosed?

The clinical features of disseminated secondary eczema are characteristic. Finding the cause depends on taking a careful history of the initial site of a skin problem. Sometimes the patient does not associate a chronic minor rash with their current widespread and symptomatic eruption.

Additional investigations that may be considered include:

• Dermatoscopy of hair shafts for nits (head lice) and burrows for scabies mites
• Swabs of crusted areas or pustules for bacteriology
• Scrapings of scaly annular or hairless plaques for mycology
• Skin biopsy of primary lesion and/or secondary rash (histology is spongiotic dermatitis)
• Blood count in an unwell patient
• Referral for patch tests, if there is suspicion of contact allergy

Patch testing should not be undertaken during the acute phase of disseminated secondary eczema, but may be planned in several months when it has settled.

What is the treatment for disseminated secondary eczema?

The primary rash needs to be treated vigorously. This may require systemic therapy, eg antibiotics for bacterid or oral antifungal for confirmed dermatophytid.

The secondary eczema is often extensive and highly symptomatic. Treatment may entail:

• Referral for specialist assessment and treatment, including admission to hospital
• Wet wraps or dressings for weeping eczematous plaques
• Potassium permanganate 1:10,000 soaks for localised oozing, infected areas
• Potent topical corticosteroid creams for 1-3 weeks
• Systemic corticosteroids, eg prednisone or prednisolone for several weeks
• Oral sedating antihistamines at night