Positive drug patch tests and the acute cutaneous adverse drug reaction share many histopathologic features

Abstract

Patch testing (PT) has been used to evaluate the culprit drug and cross-reactive chemicals in non-immediate cutaneous adverse drug reactions (CADR), but histopathology of patch tests is seldom performed. With the objective of characterizing the patterns of positive drugs patch tests in correlation with the acute skin reaction, we performed skin biopsies in 16 patients with different CADR, five cases of acute generalized exanthematous pustulosis (AGEP), six cases of maculopapular exanthema (MPE), four cases of drug reaction with eosinophilia and systemic symptoms (DRESS) and one case of toxic epidermal necrolysis (TEN). Particular macroscopic features of drug patch tests included pustules, particularly in AGEP, and epidermal necrosis in TEN and on histopathology, we highlight the occurrence of subcorneal spongiform pustules in AGEP, full-thickness epidermal necrolysis in the case of TEN and vacuolization of basal cells, lymphocyte exocytosis with occasional necrotic keratinocytes and a perivascular and interstitial lymphocyte infiltrate both in DRESS and MPE, although less intense in the latter. Similarities between the acute eruption and the patch test suggest the patch test can be considered a form of localized drug provocation test that can be used to further investigate the pathophysiology of CADR.

Keywords

• Acute generalized exanthematous pustulosis. Drug reaction with eosinophilia and systemic symptoms. Histopathology. Non-immediate drug eruptions. Patch testing. Toxic epidermal necrolysis.