Rare Lung Malignancy Mimic: A Case of Daptomycin-Induced Acute Eosinophilic Pneumonia

Daptomycin is an antibiotic used for resistant Gram-positive organisms and has the rare side effect of inducing acute eosinophilic pneumonia (AEP). This condition can be fatal due to respiratory failure if not treated, as eosinophils migrate to the lungs and inflammatory cascades cause epithelial injury. Daptomycin-induced AEP can be misdiagnosed as bacterial pneumonia or malignancy, which may lead to unnecessary testing or treatments. Diagnostic criteria include dyspnea, fever, recent daptomycin exposure, infiltrates on imaging, eosinophils on bronchoalveolar lavage or peripheral eosinophilia, and clinical improvement with medication discontinuation. We present a unique case of daptomycin-induced eosinophilic pneumonia in a 72-year-old male with the chief complaint of dyspnea and initial concerns for lung cancer after a spiculated nodule was seen on imaging. Prior to undergoing a lung biopsy, repeat imaging showed a decrease in the suspicious nodule, reducing the likelihood of malignancy and prompting a re-evaluation of the history of the present illness and medication list. Daptomycin was stopped, and the patient's symptoms and imaging improved. This case illustrates the importance of early recognition and appropriate treatment of AEP, which allows for complete clinical recovery.