The Occurrence of Different Morphological Parameters in Allergic and Irritant Patch Test Reactions

Summary

Skin-punch biopsies from 16 allergic and 13 irritant patch test reactions were evaluated in blind studies using a semiquantitative and qualitative histological registration of individual morphological parameters. Focal extension of inflammatory cells in allergic reactions was found to be statistically significantly different from diffuse extension in irritant reactions, while epidermal necrosis was found to be more pronounced in irritant reactions. Other variables which had a high value in histo-pathological diagnosis of allergic patch test reactions were the presence of oedema, lymphocytes and spongiosis; the presence of dermal and epidermal neutrophilic granulocytes was of value in the diagnosis of irritant patch test reactions.

Statistical analysis by correlation of 17 selected variables gave a diagnostic specificity of 87% and a sensitivity of 81% for allergic reactions. In irritant reactions, the specificity was 100% and the sensitivity 46%. By multiple regression analysis, an index could be calculated (4 × necrosis — 3 × oedema — 2→ ≥ 0 = irritant reaction and ≤ 0 = allergic reaction) for differentiation of allergic and irritant reactions. If this index was used in cases of allergic patch test reactions, all would be reported as allergic reactions while half of the irritant reactions would be reported as allergic. The semiquantitative and qualitative registration of histopathological parameters has shed light on the problem of histological differentiation of allergic and irritant contact dermatitis.