Eczema is largely clinically diagnosed including the employment of patch tests and other diagnostics procedures. However, the histology is useful to exclude other diagnoses like e.g. cutaneous T-cell lymphoma.
Acute eczema is characterised by spongiosis, a mainly intercellular oedema in-between the epidermal keratinocytes leading to micro- or macrovesicles. It is regularly accompanied by infiltration of leukocytes, mostly lymphocytes, into the epidermis and upper dermis.
Spongiosis is reduced and vesicles are not present anymore. The infiltration of leukocytes, mostly lymphocytes, is diminished. The epidermis thickens and parakeratosis (retention of keratinocyte nuclei in the stratum corneum) may develop.
Inflammation and spongiosis may be mild or completely absent. Thickening of the epidermis is more pronounced than in the subacute phase, as acanthosis (thickening of the stratum spinosum), hyperkeratosis (thickening of the stratum corneum) and parakeratosis (dysfunction of the keratinisation) occur.