Approach to dermal-based lymphoid infiltrates and proliferations.

The histopathological diagnosis of dermal-based lymphoid infiltrates and proliferations is often challenging due to the vast list of biologically diverse entities that archetypally or occasionally center in the mid-dermis, especially because significant overlap exists in their clinical, histopathologic, and immunophenotypic features. The differential diagnosis includes reactive infiltrates in common and rare inflammatory dermatoses, benign conditions that may mimic lymphoid neoplasms (pseudolymphomas), and true clonal proliferations arising either primarily in the skin or rarely in extracutaneous tissues with secondary cutaneous dissemination. While numerous histopathological and immunophenotypic features have been reported to support a definitive diagnosis, no single ancillary test is sufficient for their distinction.