Eosinophilic pneumonia without eosinophilia in BALF or peripheral blood and diagnosed by open lung biopsy

: A 47-year-old woman was referred to our hospital because of cough and an abnormal shadow in the left lung field. The infiltrate reduced without therapy and another infiltrate appeared in the right lung field. Bronchiolitis obliterans organizing pneumonia was clinically suspected due to the absence of signs of eosinophilia in peripheral blood and bronchoalveolar lavage fluid (BALF). Open lung biopsy specimens disclosed alveolitis with mononuclear cell infiltration and organization within the air spaces of bronchioli and alveolar ducts. The observation of pronounced eosinophil infiltration in the alveolar spaces of some specimens yielded a diagnosis of eosinophilic pneumonia. After steroid therapy, the abnormal shadows disappeared. BALF lymphocyte surface marker analysis detected no decrease in the CD4/CD8 ratio; activated CD4 and CD8 lymphocytes were notably higher than the corresponding levels in peripheral blood. IL-5, IL-3, and GM-CSF values in BALF were not significantly elevated. This was a case of borderline eosinophilic pneumonia that was difficult to diagnose on the basis of clinical parameters alone.