Approach to Cutaneous Lymphoid Infiltrates: When to Consider Lymphoma?

Cutaneous lymphoid infiltrates (CLIs) are common in routine dermatopathology. However, differentiating a reactive CLI from a malignant lymphocytic infiltrate is often a significant challenge since many inflammatory dermatoses can clinically and/or histopathologically mimic cutaneous lymphomas, coined pseudolymphomas. We conducted a literature review from 1966 to July 1, 2015, at PubMed.gov using the search terms: Cutaneous lymphoma, cutaneous pseudolymphoma, cutaneous lymphoid hyperplasia, simulants/mimics/imitators of cutaneous lymphomas, and cutaneous lymphoid infiltrates. The diagnostic approach to CLIs and the most common differential imitators of lymphoma is discussed herein based on six predominant morphologic and immunophenotypic, histopathologic patterns: (1) Superficial dermal T-cell infiltrates (2) superficial and deep dermal perivascular and/or nodular natural killer/T-cell infiltrates (3) pan-dermal diffuse T-cell infiltrates (4) panniculitic T-cell infiltrates (5) small cell predominant B-cell infiltrates, and (6) large-cell predominant B-cell infiltrates. Since no single histopathological feature is sufficient to discern between a benign and a malignant CLI, the overall balance of clinical, histopathological, immunophenotypic, and molecular features should be considered carefully to establish a diagnosis. Despite advances in ancillary studies such as immunohistochemistry and molecular clonality, these studies often display specificity and sensitivity limitations. Therefore, proper clinicopathological correlation still remains the gold standard for the precise diagnosis of CLIs.