Eczema – Basic principles/contact dermatitis
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
| Type | Variety |
|---|---|
| Exogenous (contact) | Allergic, irritant Photoreaction |
| Endogenous | Atopic Seborrhoeic Discoid (nummular) Venous (stasis, gravitational) Pompholyx |
| Unclassified | Asteatotic (eczéma craguelé) Lichen simplex (neurodermatitis) Juvenile plantar dermatosis |
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.
Chronic eczema
In chronic eczema, there is thickening of the prickle cell layer (acanthosis) and stratum corneum (hyperkeratosis) with retention of nuclei by some corneocytes (parakeratosis) (Fig. 3b). The rete ridges are lengthened, dermal vessels dilated and inflammatory mononuclear cells infiltrate the skin.
