Immunologic Overlap of Helper T-Cell Subtypes 17 and 22 in Erythrodermic Psoriasis and Atopic Dermatitis.

IMPORTANCE Psoriasis and atopic dermatitis (AD) are inflammatory diseases thought to be mediated by helper T-cell subtypes 1 and 2 (TH1 and TH2), respectively. Although psoriasis and AD show histopathologic differences during chronic disease, they are difficult to distinguish histologically during erythrodermic exacerbations. OBJECTIVE To determine whether the immune phenotype of helper T cells can differentiate erythrodermic psoriasis and erythrodermic AD by studying skin biopsy specimens of patients with psoriasis and AD during erythrodermic and chronic disease phases. DESIGN, SETTING, AND PARTICIPANTS We conducted a retrospective study using biopsy samples of psoriasis, AD, and erythroderma belonging to the surgical pathology files of the James Homer Wright Pathology Laboratories, Massachusetts General Hospital, and collected from January 1, 2004, through December 31, 2011. Samples were obtained from patients with chronic psoriasis (n = 20), chronic AD (n = 20), erythroderma subsequently diagnosed as psoriasis (n = 7), and erythroderma subsequently diagnosed as AD (n = 5). We evaluated immunohistochemical stains for CD3 and dual stains for CD4 and T-bet, GATA binding protein 3 (GATA3), signal transducer and activator of transcription 3 (STAT3), or basonuclin 2 (BNC2), which are transcription factors reported to be specific and mutually exclusive for TH1, TH2, TH17, and TH22 cells, respectively. Two investigators independently counted CD3+ cells and dual-labeled CD4+/T-bet+, CD4+/GATA3+, CD4+/STAT3+, and CD4+/BNC2+ cells in 5 consecutive high-power fields. MAIN OUTCOMES AND MEASURES We evaluated the percentage of TH1, TH2, TH17, and TH22 cells in CD3+ T cells and the TH1:TH2 ratio in chronic psoriasis, chronic AD, erythrodermic psoriasis, and erythrodermic AD. RESULTS We found a significant difference in the TH1:TH2 ratio between chronic psoriasis and chronic AD (0.26 and 0.09, respectively; P = .005). However, we detected no significant difference in the percentage of TH1 (6.5% and 4.8%), TH2 (55.2% and 64.6%), TH17 (14.7% and 30.4%), and TH22 (3.8% and 3.3%) cells of CD3+ T cells or in the TH1:TH2 ratio (0.16 and 0.07) within biopsy specimens from patients with erythrodermic psoriasis and AD, respectively. CONCLUSIONS AND RELEVANCE This study confirms the TH1- and TH2-skewed phenotype of chronic psoriasis and chronic AD, respectively. However, the immune phenotype, as determined by immunohistochemical analysis, cannot discriminate between these inflammatory diseases in the erythrodermic phase. These findings advance our understanding of the pathophysiological characteristics of erythroderma, psoriasis, and AD and may influence therapeutic decisions.