A case of marginal zone lymphoma presenting with paraneoplastic vasculitis and pulmonary infiltration.

Background: Paraneoplastic vasculitis is a rare but important manifestation of underlying malignancies, most commonly hematological, and often presents with atypical features resistant to standard immunosuppression. Marginal zone lymphoma (MZL), a low-grade B-cell lymphoma, may infrequently present with pulmonary involvement and paraneoplastic immune phenomena. Case description: We report a 73-year-old male with a history of COPD who presented with progressive dyspnoea, weight loss, lower limb purpura, and pancytopenia. Initial suspicion included pneumonia and COPD exacerbation; however, imaging revealed bilateral pulmonary infiltrates and pleural effusion. Laboratory evaluation showed systemic inflammation and worsening cytopenias. Further workup, including PET-CT and biopsies, identified CD20-positive extranodal marginal zone lymphoma with pulmonary infiltration. The patient developed presumed paraneoplastic vasculitis involving the skin and coronary arteries, in the absence of classical autoimmune markers. Rituximab monotherapy was initiated, resulting in both clinical and radiological improvement. Conclusions: This case highlights the importance of considering underlying malignancy in patients with unexplained systemic inflammation, vasculitic skin lesions, or cytopenias, particularly when autoimmune markers are negative. Prompt histological diagnosis and multidisciplinary collaboration enabled timely immunochemotherapy, resulting in the resolution of both lymphoma and associated paraneoplastic complications.