Diagnosis and management of acute eosinophilic pneumonia masquerading as malignancy and community-acquired pneumonia in an elderly male: a case report.

Background: Acute eosinophilic pneumonia (AEP) is a rare disorder characterized by febrile illness, diffuse pulmonary infiltrates, and pulmonary eosinophilia. Diagnosis is challenging, especially in elderly patients, where atypical presentations can mimic community-acquired pneumonia (CAP) or even lung malignancy. Here we report a case of AEP in an elderly male with multiple comorbidities, highlighting the diagnostic dilemma and the critical role of a multidisciplinary team (MDT) approach. Case Description: A 75-year-old male patient with a history of hypertension, type 2 diabetes mellitus, and cerebral infarction presented with a two-week history of intermittent fever and non-productive cough. Initial laboratory examinations at an outside hospital showed elevated white blood cell count and high-sensitivity C-reactive protein (CRP), with normal eosinophil count. Prior to admission, the patient had received antipyretic agents and empirical anti-infective therapy. Initial chest computed tomography (CT) revealed bilateral pulmonary infiltrates, pleural effusion, bronchial stenosis, and marked mediastinal lymphadenopathy, which was highly suggestive of malignancy. During hospitalization, the patient was treated with cefoperazone-sulbactam (2 g every 8 hours) and moxifloxacin (0.4 g once daily) for 5 days. Although the fever resolved, the imaging abnormalities persisted. Analysis of bronchoalveolar lavage (BAL) fluid showed an eosinophil percentage of 40%. A MDT consultation recommended further evaluation, and CT-guided lung biopsy confirmed interstitial eosinophilic infiltration, leading to a diagnosis of AEP. Treatment with methylprednisolone at a dose of 40 mg daily resulted in rapid clinical and radiological improvement. At 1-month follow-up, the pulmonary lesions had resolved significantly. Conclusions: This case underscores that AEP can present features highly suggestive of malignancy in elderly patients. A high index of suspicion is required when radiographic findings are incongruent with the clinical course. An MDT approach is invaluable and BAL fluid cytological analysis is a crucial diagnostic step. Lung biopsy may be necessary, in complex cases, to exclude alternative diagnosis.