Everolimus-Induced Pulmonary Toxicity in a Lung Transplant Recipient: A Case Report.

Drug-induced pneumonitis is a recognized yet often underdiagnosed complication of mammalian target of rapamycin (mTOR) inhibitors - immunosuppressive agents such as everolimus that block cellular proliferation pathways - particularly among solid organ transplant recipients. Diagnosis is frequently delayed because clinical, radiologic, and histopathologic findings can overlap with infectious or autoimmune diseases. We describe a 66-year-old man who developed progressive exertional dyspnea and facial rash six months after initiation of everolimus and 18 months after undergoing bilateral lung transplantation. He required supplemental oxygen and was admitted to a step-down respiratory care unit. Extensive infectious and autoimmune workups were negative. Lung biopsy revealed acute fibrinous and organizing pneumonia (AFOP). Everolimus was discontinued, and his immunosuppression was switched back to low-dose tacrolimus plus prednisone, leading to rapid clinical improvement and complete radiologic resolution within four weeks. This case underscores the need for high clinical suspicion of everolimus-induced pneumonitis in transplant recipients presenting with new pulmonary infiltrates and highlights the importance of early drug discontinuation guided by histopathologic confirmation to prevent progression to respiratory failure.