Definition

Eczema is a non-infective inflammatory skin condition that shows itching, redness and scaling. Eczema represents a reaction pattern to a variety of stimuli, some of which are recognized but many of which are unknown. Eczema and dermatitis mean the same thing and may be used interchangeably. ‘Atopy’ defines those with an inherited tendency to develop asthma, allergic rhinitis, conjunctivitis or atopic eczema and is present in 15–25% of the population. Atopics produce high levels of circulating immunoglobulin (Ig) E antibodies, commonly to inhalant allergens (e.g. house dust mite).

Classification

The current classification of eczema is unsatisfactory in that it is inconsistent. However, it is difficult to provide a suitable alternative as the aetiology of most eczemas is not known. Different types of eczema may be recognized by morphology, site or cause. A division into endogenous (due to internal or constitutional factors) and exogenous (due to external contact agents) is convenient (Table 1). However, in clinical practice, these distinctions are often blurred and, not infrequently, the eczema cannot be classified. A further division into acute (Fig. 1) and chronic (Fig. 2) eczema can be made in many cases according to the morphology of the eruption.

Table 1 A classification of eczema

Fig. 1 Acute dermatitis (eczema).

Erythema and oedema are seen with papules, vesicles and sometimes large blisters. Exudation and crust formation follow. The eruption is painful and pruritic. This case resulted from a contact allergy to a locally applied cream.

Fig. 2 Chronic dermatitis (eczema).

Lichenification, scaling and fissuring of the hands due to repeated exposure to irritants. Allergic contact dermatitis cannot be excluded on the appearance alone.

Acute eczema

In acute eczema, epidermal oedema (spongiosis), with separation of keratinocytes, leads to the formation of epidermal vesicles (Fig. 3a). Dermal vessels are dilated, and inflammatory cells invade the dermis and epidermis.

Fig. 3 The histology of (a) acute and (b) chronic dermatitis.

Definition