Antisynthetase Syndrome Masquerading as Hypersensitivity Pneumonitis.

Interstitial lung diseases (ILDs) cover a wide heterogeneous group of disorders, both of unknown and known causes. Accurate diagnosis is essential but, at the same time, presents many challenges. Typically, the distinction between idiopathic pulmonary fibrosis and fibrotic hypersensitivity pneumonitis (HP) can prove extremely difficult. However, another major, but underestimated, challenge is the diagnosis of connective tissue disease-associated ILD (CTD-ILD), specifically when ILD is the initial manifestation or when extrapulmonary manifestations are subclinical. Antisynthetase syndrome (ASyS) is a characteristic example where lung involvement can be the predominant feature in the absence of other evidence suggestive of CTD. In ASyS, lung involvement can be the initial manifestation or muscle involvement can be subclinical with normal muscle enzymes. Furthermore, a negative antinuclear antibody test does not indicate autoantibody negativity in the context of ASyS. Imaging and pathology findings in ASyS are not specific and overlap with other ILDs. Finally, bronchoalveolar lavage can exhibit pronounced lymphocytosis (>30-40%). The latter, in combination with a history of exposure to an inciting antigen, can lead to an erroneous diagnosis of HP with obvious negative impact on patients' outcome. Herein, we report 3 female patients aged 61, 65, and 70 years and 1 male patient aged 43 years, with ASyS masquerading as HP and analyze the underlying reasons of misdiagnosis, aiming to raise awareness of the need for close collaboration between pulmonologists and rheumatologists.