Differentiating Psoriasis From Dermatitis With Interleukin-36 Gamma Immunohistochemistry on Skin Biopsy Specimens: A Retrospective, Single-Center Validation and Cohort Study

Summary: OBJECTIVES To validate IL-36 to differentiate psoriasis from spongiotic dermatitis in clear-cut and ambiguous cases. METHODS A retrospective Institutional-Review-Board-approved single-center validation and cohort study compared IL-36 gamma expression in formalin-fixed, archived skin-biopsy tissue of clear-cut cases of psoriasis vs. eczema, and in histopathologically ambiguous cases of “psoriasiform dermatitis” in patients with clinical features of either psoriasis or eczema. Expression patterns were semi-quantitatively rated 0-4, being 0-2 considered negative, and 3-4, positive. RESULTS In clear-cut cases of psoriasis (n=31) or spongiotic dermatitis (n=23), test sensitivity and specificity of IL36 gamma were 80.6% and 100%, respectively (area-under-curve= 0.9032). In histopathologically ambiguous cases of psoriasiform dermatitis with clinical features favoring either psoriasis (n=14) or spongiotic dermatitis (n=11), test sensitivity and specificity were 78.6% or 100%, respectively (area under-curve= 0.8929). CONCLUSION Positive IL-36 gamma IHC expression appears to correlate well with a clinical diagnosis of psoriasis over eczematous dermatitis, even when histopathology is ambiguous. Future studies could explore the relationship between IL-36 gamma IHC expression and disease activity or response to biologic therapies.