A43-07 Cystic Lung Disease as a Presentation of Hypersensitivity Pneumonitis: A Series of Five Clinical Cases

Abstract Introduction Hypersensitivity pneumonitis (HP) is an inflammatory and fibrotic disease affecting the lung parenchyma and small airways. It is usually the result of an immune-mediated reaction to an overt or occult inhaled antigen in genetically susceptible individuals. It is classified according to the latest consensus as non-fibrotic (pathologically inflammatory) and fibrotic (including fibroinflammatory findings on both chest imaging and pathology) (1). Up to 10% of cases may present as diffuse cystic lung disease on debut. Five cases are presented, with their respective clinical, radiological and pathological correlations. Clinical cases The following are five clinical cases of patients with cystic lung disease who, after extensive clinical, radiological, immunological and pathological analysis, were diagnosed with HP. The cysts observed in these patients were thin-walled, randomly distributed and some associated with ground-glass opacities, without a specific radiological pattern. From an anatomopathological point of view, chronic bronchiolocentric inflammation with poorly formed granulomas was evident, characteristic findings of non-fibrosing HP (Figure 1). It is suggested that HP may present with cysts due to the histological development of a lymphocytic infiltrate similar to that observed in lymphocytic interstitial pneumonia, which generates partial bronchial obstruction, favouring the formation of cysts within the lung tissue. Therefore, in the case of a patient with risk factors for this entity, histopathological study would be indicated. Discussion HP accounts for approximately 15% of all interstitial lung diseases (ILDs), although its prevalence varies geographically (2)(3). Moreover, 30-40% of patients with ILD (including HP) may evolve over time toward a progressive fibrosing phenotype (4)(5). By definition, the typical non-fibrotic HP pattern is characterized by centrilobular ground-glass nodules, mosaic attenuation and airway-centered involvement. In fibrotic HP, additional coarse reticulation and a bronchiolocentric distribution pattern are observed. However, approximately 10% of HP cases may present with cystic lesions that are usually sparse, diffuse and randomly distributed (6). As noted by Tinoco et al. (7), most reported cases occur in non-fibrotic HP, involving 5% of the lung parenchyma, with cysts measuring 3-25 mm in diameter and associated ground-glass opacities. Differential diagnoses in this context include alveolar macrophage pneumonia (previously “desquamative interstitial pneumonia”) and Pneumocystis jirovecii infection (8). Only a few case reports describe patients with HP presenting as diffuse cystic lung disease. Similar to the bronchiolocentric interstitial pneumonia pattern (5), we propose that in selected cases of diffuse cystic lung disease, an early decision to perform lung biopsy—preferably cryobiopsy—should be considered (9,10). This abstract is funded by: None