Drug Hypersensitivity: A Correlation Study From Histopathology to Clinic

ABSTRACT Background Drug hypersensitivity (DH) can present with varied clinical and pathological manifestations that may mislead the referring physician. Available data regarding the concordance between pathological diagnosis and clinical findings in DH are scarce. Objectives We aimed to describe the clinical spectrum of patients with an established histological diagnosis compatible with DH. Methods We conducted a retrospective single‐centre study of adult patients using a coding system for pathological results for skin biopsy between 2011 and 2019. Clinical correlation was then analysed through the medical records. Results A total of 408 biopsies were analysed. The differential diagnosis of DH was considered by the referring physician in 57% of cases ( n = 217), and the introduction of a new drug was reported in 63% of cases ( n = 237). In 19% of cases ( n = 70), DH was the only histological diagnosis provided by the reporting pathologist, whereas an alternative diagnosis was suggested in the remaining cases. After review of the pathological report, a final clinical diagnosis of DH was retained by the referring physician in 46% of cases ( n = 165/355), suggesting limited concordance between pathological findings and clinical review. When the diagnosis of DH was initially suggested by the referring physician, this diagnosis was confirmed in 67% of cases ( n = 145/217). The diagnosis of DH was made in 5 cases (1%) following the pathological examination when the referring physician did not initially propose a diagnosis of DH following clinical examination. In 25% of cases, the pathologist provided a final diagnosis of drug‐induced maculopapular exanthem (MPE), viral exanthem or eczema for the same biopsy, highlighting that the histological features of these three conditions can appear very similar and difficult to distinguish. Conclusions Pathological to clinical correlation must be considered, particularly in the context of DH. Our study confirms a limited benefit from skin biopsying in cases of drug‐induced MPE.