Inflammatory Dermatopathology

Abstract

CD30 is a marker of lymphoid activation that is characteristically expressed in lymphoproliferative disorders such as anaplastic large cell lymphoma (ALCL), lymphomatoid papulosis (LyP) and Hodgkin lymphoma, but also in other T- and B-cell lymphomas, and in cutaneous lymphoid hyperplasia. However, CD30 expression can also be found in a wide variety of inflammatory and infectious skin conditions including immune-mediated disorders (eg, atopic dermatitis, pityriasis lichenoides, scleroderma, graft versus host disease), drug reactions (eg, antibiotics, chemotherapeutic agents), viral infections (eg, molluscum contagiosum, parapoxvirus, herpes simplex virus, human immunodeficiency virus), bacterial and fungal infections (eg, abscesses, cellulitis, chromomycosis), environmental conditions (eg, scabies, insect and spider bites), peritumoral host responses (eg, basal cell carcinoma, cutaneous lymphadenoma) and in other miscellaneous disorders (eg, hidradenitis suppurativa, ruptured cysts, pressure ulcers, granulation tissue). Moreover, CD30 expression can also be found in nonhematolymphoid cells such as germ cells and mesothelial cells. In inflammatory skin conditions, atypical CD30+ lymphoid cells may cause differential diagnostic problems with CD30+ lymphoproliferative disorders. It is obvious that the sole presence of CD30+ atypical cells in the skin can not in itself support a malignant diagnosis. The differentiation between benign and malignant cutaneous lymphoid infiltrates is only possible through the combined use of multiple clinical, histologic, immunophenotypic and molecular genetic analyses, as there is no single reliable criterion that would allow this distinction. Large atypical CD30+ lymphoid cells are a part of cutaneous reactive infiltrates and do not qualify alone for the diagnosis of malignancy.