Eosinophils are rare in biopsy specimens of psoriasis vulgaris

Histological features of lesional biopsies can be helpful in distinguishing psoriasis subtypes from disease mimickers. However, occasionally, classic histological features are not sufficient for distinction, and additional clues would be useful. There is a common belief that the presence of eosinophils in skin biopsies argues against psoriasis, but actual literature is scant.

Skin biopsies with a diagnosis of psoriasis from 2013 to 2016 were reviewed. For inclusion, both histological and clinical features were required to be consistent with psoriasis. For biopsies meeting inclusion criteria, a detailed evaluation for typical histological parameters of psoriasis, as well as presence of dermal eosinophils, was performed.

Of 85 cases meeting inclusion criteria, all had either individual or grouped intracorneal neutrophils and dilated papillary blood vessels. Diminished or complete loss of the granular cell layer was seen in 83 cases (98%), and parakeratosis was seen in 84 cases (99%). Alternatively, dermal eosinophils were seen in only 15 cases (18%). Of cases with eosinophils, none had more than 3 eosinophils upon examination of the entire dermis. Active treatment did not appear to impact presence/absence or numbers of eosinophils.

Eosinophils are uncommon in psoriasis biopsies, and when present, they are found in small numbers.