Ki-1—positive anaplastic large-cell lymphoma can mimic benign dermatoses

Background: Regressing atypical histiocytosis is a recently described disease characterized by recurrent nodules or ulcers. The cutaneous lesions appear abruptly and then regress only to return in a manner reminiscent of lymphomatoid papulosis. Immunophenotypic analysis has revealed that most cases are a form of anaplastic large-cell Ki-1—positive (CD30⁺) lymphoma. Objective: We describe two patients with Ki-1—positive anaplastic large-cell lymphoma that had clinical and pathologic features of regressing atypical histiocytosis and mimicked benign dennatoses (pyoderma grangrenosum and morphea), causing a delay in confirming the true diagnosis. A third case that was readily recognized as a lymphoma is also presented. Methods: The clinical and histopathologic findings were recorded. In addition, T-cell receptor gene rearrangement and immunophenotyping were determined in the index case. Results: The index patient and second patient were diagnosed as having Ki-1—positive anaplastic large-cell lymphoma by immunophenotyping and underwent cyclophosphamide, doxorubicin, prednisone, and vincristine (CHOP) chemotherapy with complete remission. The patient detected by chart review died of her disease without receiving antineoplastic therapy; disseminated lymphoma was diagnosed at autopsy. Studies on paraffin-embedded tissue were consistent with Ki-1—positive anaplastic large-cell lymphoma. Conclusion: Regressing atypical histiocytosis may clinically resemble some benign dermatoses. Recent evaluation of these cases has shown that many represent a form of Ki-1—positive anaplastic large-cell lymphoma. Multiple skin biopsy specimens with immunophenotyping and gene rearrangement studies are required to arrive at the diagnosis.