Eosinophils Among the Histological Features of Psoriasis

"Eosinophils are absent in psoriasis" has been dogma for generations; yet, there is little published to support this statement. Two recent studies examining the presence of eosinophils in psoriasis came to contrasting conclusions. We reviewed skin biopsies from 50 patients with clinically confirmed cases of psoriasis vulgaris to characterize the histologic features, with a focus on the number of eosinophils in the dermis. We noted the presence of eosinophils in nearly half of our study population (n = 23, 46.0%). There was no significant association between the presence of eosinophils and degree of spongiosis (P = 0.405). Eosinophil density ranged from 0 to 8 per tissue section. The mean average eosinophil density was 1.04 (range: 0-8) per tissue section. Among cases with eosinophils, there were 73.9% (n = 17/23) of cases with 1-2 eosinophils, and 26.1% (n = 6) with 3-8 eosinophils. Mild to moderate spongiosis was noted in the majority of cases (n = 48; 96.0%). Eosinophils were only present in psoriasis cases with evidence of spongiosis (n = 23; 47.9%). We conclude that eosinophils are not an uncommon finding in the dermis of psoriasis vulgaris, although the number is often few. The presence of eosinophils should not preclude a diagnosis of psoriasis, particularly if other histologic features are supportive.