The spectrum of histopathological features in acute generalized exanthematous pustulosis: a study of 102 cases

Background Acute generalized exanthematous pustulosis (AGEP) is a rare severe pustular reaction pattern with a typical clinical picture. Objectives To characterize the histopathological features of AGEP in a large series of cases with a validated diagnosis. Methods A multinational retrospective histopathological study was conducted. It included 102 hospitalized patients (recruited within the EuroSCAR and RegiSCAR studies) with a validated diagnosis of probable or definite AGEP. A systematic description of the histopathological features in AGEP was done based on a standardized grading system. Results Sub/intracorneal pustules (41%), intraepidermal pustules (20%) or combinations of them (38%) were observed in 102 cases. The pustules were usually large (> 15 keratinocytes) (82% and 89%, respectively) and regularly contained eosinophils (36% and 32%, respectively). Spongiform features were less prominent in the sub/intracorneal pustules compared with the intraepidermal pustules (44% and 95%, respectively). The main epidermal features were necrotic keratinocytes (67%), including incidental segmental necrosis (7%), and spongiosis (80%) with neutrophil exocytosis (77%). The main dermal features were papillary oedema (88%) and mixed superficial (100%), interstitial (93%), and mid/deep-dermal infiltrates (95%) containing neutrophils (100%) and eosinophils (81%). Follicular pustules were also seen (23%), but vasculitis generally was absent. Classical features of plaque-type psoriasis were infrequent and usually mild. No significant differences were observed between a subgroup of 16 cases with and 86 cases without psoriasis. Conclusions The present histopathological study concerns a large series of cases with a validated diagnosis of AGEP. It provides diagnostic clues in favour of AGEP in patients with a pustular eruption.