Human T-cell lymphotropic virus type 1 (HTLV-1)-associated bronchioloalveolar disorder required differentiation from fibrotic chronic hypersensitivity pneumonitis.

We encountered a case of HTLV-1-associated bronchioloalveolar disorder (HABA) that was difficult to distinguish from fibrotic chronic hypersensitivity pneumonitis (CHP). Chest thin-section computed tomography (CT) showed diffuse micronodules and revealed peribronchovascular and perilobular distribution. Further, thickening of the interlobular septa, areas of ground-glass attenuation, traction bronchiectasis/bronchiolectasis, and air trapping were observed. Based on these findings, diseases that cause lymphatic tract abnormalities and fibrotic CHP were considered differential diseases. A surgical lung biopsy was performed, and an HTLV-1 antibody was detected using the Western blot analysis of bronchoalveolar lavage fluid. The final diagnosis of HABA was made through a multidisciplinary discussion.