Diffuse Large B-Cell Lymphoma Presenting Primarily as a Cutaneous Leg Lesion: A Case Report and Literature Review.

Primary cutaneous B-cell lymphoma (PCBCL) has three subtypes, among those, the leg type variant is the rarest with the highest rates of relapse and recurrence making it an intriguing focus for researchers. Nevertheless, prior to framing a diagnosis solely based on the lesion's location, it is prudent to reconsider whether it is genuinely a primary cutaneous B-cell lymphoma (PCBCL) or if it aligns more closely with the more prevalent lymphoma variants such as diffuse large B-cell lymphoma (DLBCL) with cutaneous involvement. We are reporting a case of an 85-year-old African American lady, who presented with unilateral left leg DLBCL with cutaneous involvement. The patient was treated for recurrent cellulitis that was non-responsive to antibiotics; this prompted evaluation by leg MRI, which revealed a mass-like lesion involving the skin and muscle. Additional workup, which included tissue diagnosis and immunohistochemistry (IHC) studies, confirmed the diagnosis of DLBCL. A thorough clinical, laboratory, and imaging workup revealed diffuse meningeal lymphomatous involvement on brain MRI. The patient was started on reduced-intensity rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone (R-mini-CHOP) protocol with granulocyte-colony stimulating factor (G-CSF) and showed a good initial response. This case highlights the importance of comprehensive evaluation in distinguishing primary cutaneous B-cell lymphomas from other variants, particularly in atypical presentations such as diffuse involvement.