Histologic comparison of tumor necrosis factor-α inhibitor-induced psoriasis and psoriasis vulgaris

Tumor necrosis factor-α inhibitor (TNFi)-induced psoriasis is a paradoxic reaction characterized by the development of a psoriasiform rash that mimics idiopathic psoriasis subtypes both clinically and histologically. Few studies have investigated the histologic features of TNFi-induced psoriasis skin lesions, and most of these are limited by inclusion of few specimens.

We aimed to characterize histologic features of TNFi-induced psoriasis and identify histologic differences between TNFi-induced psoriasis and idiopathic psoriasis.

We characterized 60 biopsy specimens obtained from 47 unique patients at a single tertiary care referral center between 2004 and 2016 who developed TNFi-induced psoriasis, and we compared histologic features to those of 85 biopsy specimens from a control group of 85 patients with idiopathic psoriasis.

The most common histologic reaction pattern in TNFi-induced psoriasis biopsy specimens was psoriasiform (80.0%). Five histologic parameters were significantly different in TNFi-induced psoriasis biopsy specimens compared with idiopathic psoriasis biopsy specimens: at least 3 dermal eosinophils per histologic section, neutrophils in the stratum corneum, neutrophils in the epidermis, papillary plate thinning, and absence of parakeratosis.

Inability to exclude lesion selection bias as a potential reason for some significant histologic differences.

This study supports the idea that histologic differences exist between TNFi-induced psoriasis and idiopathic psoriasis may help distinguish between these conditions, especially for dermal eosinophil counts of 3 or greater.