Differential diagnosis between cutaneous lymphoma and pseudolymphoma

Differential diagnosis of cutaneous lymphoproliferative disorders represents one of the most vexing problems in dermatology and dermatopathology. For nearly a century the diagnosis has been based only upon clinicopathologic correlation. Immunohistochemical and molecular techniques developed during the last 3 decades added new criteria for the differentiation of these diseases. The purpose of this article is to summarize the criteria for the differential diagnosis of benign vs. malignant lymphoid infiltrates of the skin. In this context, a proper classification of cutaneous lymphoproliferative disorders can be achieved only by a synthesis of clinical, histopathologic, immunophenotypic and molecular criteria, and in some cases only follow-up data allow a precise diagnosis to be made.