Avoid a rash diagnosis: Cytophagic histiocytic panniculitis is a distinct clinical entity

Abstract Background: Cytophagic histiocytic panniculitis (CHP) is a rare autoimmune disease that can mimic both lupus panniculitis (LP) and subcutaneous panniculitis-like T cell lymphoma (SPTL). Diagnosis is challenging due to overlapping histologic characteristics of these entities. It has historically been considered a pre-malignant lesion, with few case reports detailing CHP as its own entity.Case Presentation: We describe two cases of panniculitis with histologic features similar to both LP and SPTL. Neither patient had clinical or laboratory features convincing of systemic lupus erythematosus (SLE), which made a diagnosis of LP unlikely; T-cell receptor (TCR) gene rearrangement studies demonstrated a polyclonal lymphocytic infiltrate, suggestive of a non-malignant process. Both patients were diagnosed with CHP and responded well to tacrolimus therapy. Conclusions: CHP is a distinct clinical entity, and the panniculitis need not fall under a diagnosis of LP or SPTL. TCR gene rearrangement studies are an essential part of the evaluation to demonstrate polyclonality of the benign lymphocytic infiltrate. T-cell directed therapy represents a rational approach to treatment and yielded success in these two patients.