Pretibial Pruritic Papular Dermatitis: A Comprehensive Clinical and Pathologic Review of Cases at a Single Institution.

Background: Studies characterizing clinical and pathologic details of pretibial pruritic papular dermatitis (PPPD) are scarce. Several cases of PPPD at our institution have displayed lymphocyte atypia and CD30 positivity, resembling lymphomatoid papulosis (LyP). We explore the clinical and histological spectrum of PPPD, with emphasis on lymphocyte atypia.

Methods: Retrospective observational study of 40 archived pathological specimens (hematoxylin/eosin, CD3, CD20, and CD30 immunohistochemistry) from 38 PPPD patients in an academic center. Clinical photographs were available in 22 cases.

Results: Microscopic epidermal changes were focal, but common (spongiosis 75%, parakeratosis 90%, interface changes 43%, Langerhans cell microgranulomas 25%, multinucleated keratinocytes 55%, Civatte bodies 55%, erosion 20%, and more than focal irregular psoriasiform hyperplasia 37%) and certain dermal changes were universal (papillary dermal fibrosis 100%, stellate fibroblasts 100%, and multinucleated fibroblasts 93%). At least focal lymphocyte atypia was present in all cases. Lymphocytes were almost exclusively CD3 T cells with rare CD20 B cells. Up to 30% of lymphocytes exhibited weak CD30 staining. Clinically, all cases exhibited discrete papules, but plaques and erosions were not uncommon.

Limitations: As a retrospective series, clinical images were not available for all cases.

Conclusion: This study suggests a broader histological and clinical spectrum of PPPD than previously described. Epidermal changes are common in PPPD, as are atypical lymphocytes and focal CD30 positivity. Although the papular clinical appearance, lymphocyte atypia, and focal CD30 positivity may resemble LyP, the relatively low number of atypical lymphocytes, low intensity of CD30 staining, and absence of spontaneous resolution help to distinguish PPPD from LyP.