Differential Diagnosis of Eosinophilic Lung Diseases.

Eosinophilic lung diseases encompass a heterogeneous spectrum of disorders characterized by the accumulation of eosinophils within the lung parenchyma. Etiologies range from primary eosinophilic syndromes to secondary causes such as parasitic and fungal infections, hematologic malignancies, allergic conditions, and systemic autoimmune diseases. Given their overlapping clinical and radiologic presentations, accurate and timely diagnosis is critical for guiding appropriate management and avoiding both overtreatment and delays in therapy. This review synthesizes current evidence and expert perspectives on the differential diagnosis of eosinophilic lung diseases, drawing on clinical, laboratory, radiologic, and histopathologic approaches. Key emphasis is placed on distinguishing primary eosinophilic syndromes from secondary causes, the role of molecular and immunologic testing, and the integration of multidisciplinary expertise. A comprehensive diagnostic algorithm is presented to assist clinicians in routine practice, with particular emphasis on addressing unmet needs such as biomarker development and the establishment of standardized definitions for disease activity. By elucidating diagnostic processes and minimizing common errors, this article seeks to enhance the precision of differential diagnosis and improve clinical outcomes for patients with eosinophilic lung involvement.