Abstract

Psoriasis is an inflammatory skin disease driven by the T helper (Th)17/Th22 pathway, which stimulates keratinocyte production of interleukin (IL)-36. Psoriatic skin robustly expresses IL-36 in the upper epidermis, and immunostaining for IL-36 can help to distinguish psoriasis from other inflammatory skin diseases. We assessed the utility of IL-36 immunostaining to distinguish psoriasis from 2 skin diseases with psoriasiform inflammatory patterns, namely pityriasis rosea (PR) and pityriasis lichenoides (PL). We stained 21 PR and 22 PL specimens for IL-36 and graded the immunostaining as 0, negative; 1, focal weak; 2, diffuse weak; 3, focal, strong; or 4, diffuse strong. Ten psoriasis specimens served as the control group. We further categorized stains into a dichotomous result as negative (0-2 score) or positive (3-4 score) and utilized Fisher’s exact test to compare the immunostaining pattern of psoriasis against PR and PL. All psoriasis specimens were positive; all specimens of PR were negative (p= 0.00000002). Twenty PL specimens were negative (p= 0.000001), with 9 of 10 pityriasis lichenoides et varioliformis acuta cases being negative (p= 0.00012) and 11 of 12 cases of pityriasis lichenoides chronica being negative (p= 0.00003). This study is the first to compare the IL-36 immunostaining pattern of psoriasis against PL and PR and demonstrates the great promise of the immunostain in distinguishing PL and PR from psoriasis in routine skin biopsies.