When the Treatment Becomes the Threat: A Case of Rituximab-Induced Organizing Pneumonia

Rituximab (RTX) is a chimeric monoclonal antibody against CD20-expressing B lymphocytes, widely used in B-cell malignancies.Although generally well-tolerated, pulmonary toxicity is a rare but potentially fatal complication.A 71-year-old male with hepatic non-Hodgkin lymphoma (NHL) in remission, on maintenance RTX, presented with a one-month history of fever, asthenia, and progressive dyspnea.Initial management for suspected community-acquired pneumonia with levofloxacin failed.Despite temporary improvement on piperacillin/tazobactam, symptoms recurred after discharge, progressing to hypoxemic respiratory failure.Extensive workup, including bronchoalveolar lavage (BAL) and positron emission tomography-computed tomography (PET-CT), ruled out infection and lymphoma relapse.Following a multidisciplinary review, RTX-induced organizing pneumonia (OP) was suspected.Initiation of high-dose methylprednisolone (250 mg/day) led to rapid clinical and radiological resolution.RTX-induced OP requires a high index of suspicion, as its clinical-radiological presentation mimics infectious pneumonia.Early recognition and prompt initiation of corticosteroids are associated with rapid clinical and radiological recovery and may reduce the risk of progression to irreversible pulmonary fibrosis.