Classification of eczema
This is a messy legacy from a time when little was known about the subject. As a result, some terms are based on the appearance of lesions, e.g. discoid eczema and hyperkeratotic eczema, while others reflect outmoded or unproven theories of causation, e.g. infective eczema and seborrhoeic eczema. Classification by site, e.g. flexural eczema and hand eczema, is equally unhelpful.
Eczema is a reaction pattern. Many different stimuli can make the skin react in the same way, and several of these may be in action at the same time (Fig. 7.1). This can make it hard to be sure which type of eczema is present; and even experienced dermatologists admit that they can only classify some two-thirds of the cases they see. To complicate matters further, the physical signs that make up eczema, although limited, can be jumbled together in an infinite number of ways, so that no two cases look alike.
One time-honoured subdivision of eczema is into exogenous (or contact) and endogenous (or constitu-tional) types. However, it is now clear that this is too simple. Different types of eczema often overlap, e.g. when a contact eczema is superimposed on a gravita-tional one. Even atopic eczema, the type most widely accepted as endogenous, is greatly influenced by external ‘flare factors’aand itself predisposes to the development of irritant contact dermatitis, e.g. caused by soap. Nevertheless, it is still true that any rational approach to any patient with eczema must include a search for remediable environmental factors.
A working classification of eczema is given in Table 7.1.