LAUSR

BACKGROUND Tumor necrosis factor-α inhibitor-induced psoriasis (TNFI-psoriasis) is a paradoxical reaction characterized by development of a psoriasiform rash that mimics idiopathic psoriasis subtypes both clinically and histologically. Few studies have investigated histologic features of TNFI-induced psoriasis skin lesions, and most of these are limited by inclusion of few specimens. OBJECTIVE We aimed to characterize histologic features of TNFI-psoriasis and identify histological differences between TNFI-psoriasis and idiopathic psoriasis. METHODS We characterized 60 biopsies obtained from 47 unique patients at a single tertiary care referral center between 2004-2016 who developed TNFI-psoriasis, and compared histologic features to those in 85 biopsy specimens from a control group of 85 patients with idiopathic psoriasis. RESULTS The most common histologic reaction pattern in TNFI-psoriasis biopsies was psoriasiform (80.0%). Five histological parameters were significantly different in TNFI-psoriasis biopsies compared to idiopathic psoriasis biopsies: ≥3 dermal eosinophils per histologic section, neutrophils in the stratum corneum, neutrophils in the epidermis, papillary plate thinning, and absence of parakeratosis. LIMITATIONS Inability to exclude lesion selection bias as a potential reason for some significant histologic differences. CONCLUSION This study supports that histological differences exist between TNFI-psoriasis and idiopathic psoriasis that may help distinguish between these conditions, especially dermal eosinophil counts ≥3.