1436 Lesional Skin Histology in Drug-Induced Hypersensitivity Syndrome: A Single Center 10-Year Experience of 37 Patients

Introduction: Histopathological features of drug-induced hypersensitivity syndrome (DIHS) are known to be variable. Here, we report a retrospective analysis of skin histology in DIHS patients treated at our department over the last decade. Study population: Patients with clinical diagnosis of DIHS who underwent lesional skin biopsy at the Niigata University Hospital between 2010 and 2022 were included. The exclusion criteria were skin drug reactions other than DIHS and comorbid skin diseases. Methods: Skin biopsy specimens stained with hematoxylin & eosin were independently evaluated by two authors (EB and OA) and were graded for necrotic keratinocytes, spongiosis, epidermal lymphocytes, interface dermatitis, melanin incontinence, perivascular infiltration, leukocytoclasis, and red blood cell (RBC) extravasation. Eosinophils were counted in at least three high power fields (HPF) at a magnification 400. Results: In total, 37 patients (19 males) with a median age of 68 [IQR 61;75] years were included. Necrotic keratinocytes occurred in 20 (54%) patients, spongiosis - in 27 (72,9%). Interface dermatitis was noted in 34 (91,9%) patients. Perivascular infiltration was moderate (n=18) and marked (n=5) in 23 (62,2%) patients. There was leukocytoclasis with or without RBC extravasation in 16 (43,2%) patients. In skin biopsies, 2-5 eosinophils/HPF were consistently present in nine (24,3%) patients, whereas occasional eosinophils were noted in four additional cases. Conclusions: This study is based on a large series of DIHS patients from a specialized tertiary center although its limitations are inherent in its retrospective design and single center setting. Our study revealed interface dermatitis, to a varying degree, as the most common feature (>90%) of DIHS, followed by dyskeratosis (54%), vasculitic changes (43,2%) and local eosinophilia (24,3%). Whether these changes represent a histological spectrum or pathophysiological stages of DIHS is yet to be established.