Case Report: Chronic eosinophilic pneumonia with acute-like presentation and diagnostic challenges.

Background: Chronic eosinophilic pneumonia (CEP) is a rare eosinophilic lung disease characterized by pulmonary and peripheral blood eosinophilia. It predominantly affects middle-aged women and remains a diagnosis of exclusion based on compatible clinical and imaging findings together with the absence of secondary causes. Distinguishing CEP from acute eosinophilic pneumonia (AEP) or infectious processes may be challenging, particularly in atypical presentations. Systemic corticosteroids represent the standard therapy and typically produce rapid clinical improvement, although relapse is common after treatment tapering or withdrawal. Case presentation: We report the case of a 65-year-old female smoker presenting with persistent cough, dyspnea, and chest pain, initially treated as community-acquired pneumonia. The diagnostic work-up included laboratory testing, pulmonary function assessment, high-resolution computed tomography (HRCT), bronchoscopy with bronchoalveolar lavage (BAL) and bronchial biopsy. Peripheral eosinophilia and elevated inflammatory markers were observed. HRCT demonstrated bilateral upper-lobe-predominant consolidations associated with centrilobular opacities and tree-in-bud changes. Microbiological and parasitological investigations were negative. BAL did not demonstrate eosinophil predominance; however, bronchial biopsy revealed eosinophil-rich inflammatory infiltrates. After exclusion of infectious and parasitic causes and integration of clinical, imaging, and histopathological findings, a diagnosis of chronic eosinophilic pneumonia was established. Oral methylprednisolone (16 mg/day) was administered for approximately 8-10 weeks, followed by gradual tapering to 8 mg/day, resulting in marked clinical and radiological improvement. One month after corticosteroid withdrawal, symptoms recurred, requiring treatment reintroduction. Follow-up HRCT demonstrated complete resolution of the consolidations. An exploratory attenuation-based aeration analysis suggested regional hyperaeration in areas previously affected by consolidation, although its clinical significance remains uncertain. Conclusion: This case illustrates the diagnostic complexity of CEP when acute-like clinical features, atypical imaging findings, and discordant bronchoalveolar lavage results coexist and highlights the importance of integrating clinical, imaging, microbiologic and histopathological data to establish the diagnosis.