A rare case of mantle cell lymphoma involving the toes

Summary: A 56-year-old previously healthy male presented to clinic with edematous plaques on the distal aspect of multiple unilateral toes. Having progressed over multiple years, the lesions were painful and associated with onychodystrophy. A skin biopsy demonstrated multinodular infiltrates of small- to medium-sized atypical lymphocytes within the dermis and subcutis. Immunohistochemical staining revealed a primary B-cell population which was diffusely positive for CD20 and BCL2 and focally positive for BCL1. These cells were negative for CD5, BCL6, SOX-11, and LEF1. In situ hybridization studies demonstrated lambda light chain restriction. FISH testing for cyclin D1 was positive. These findings were compatible with a primary cutaneous mantle cell lymphoma affecting multiple toes. Mantle cell lymphoma (MCL) is an aggressive subtype of non-Hodgkin’s lymphoma which has been rarely reported to involve the skin, often in the setting of systemic disease. However, there are few reports of primary cutaneous MCL. The present case is unique in both the clinical presentation of progressive plaques on multiple toes and in the negativity for CD5 and SOX-11, both of which tend to be positive in most cases of MCL. Further research is needed to delineate whether cutaneous involvement by systemic MCL has a distinct clinical and/or pathological presentation.