Significance of Myositis Autoantibody in Patients with Idiopathic Interstitial Lung Disease

PURPOSE Some patients with interstitial lung disease (ILD) related to connective tissue disease (CTD) have a delayed diagnosis of the underlying CTD when the ILD is categorized as idiopathic. In this study, we evaluated the frequency of myositis autoantibodies in patients diagnosed with idiopathic ILD and investigated the clinical significance stemming from the presence of the antibodies. MATERIALS AND METHODS A total 32 patients diagnosed with idiopathic ILD were enrolled in this study. We analyzed a panel of 11 myositis autoantibody specificities in the patients using a line blot immunoassay. Then, we divided them into myositis autoantibody-positive and -negative groups and compared the clinical features and laboratory data between the two groups. RESULTS Of the 32 idiopathic ILD patients, 12 patients had myositis autoantibodies encompassing 9 specificities, except for anti-Mi-2 and anti-PM-Scl 100 (12/32, 38%). Anti-synthetase autoantibodies including Jo-1, EJ, OJ, PL-7, and PL-12 were present in 7 patients (7/32, 22%). The group with myositis autoantibodies presented more frequently with the symptom of mechanic's hand and showed abnormal pulmonary function test results with low forced vital capacity, diffusing capacity for carbon monoxide, total lung capacity, and high lactate dehydrogenase values in blood when compared with the group without myositis antibodies. CONCLUSION We strongly suggest that patients undergo an evaluation of myositis autoantibodies, if they are diagnosed with idiopathic ILD in the presence of clinical characteristics including mechanic's hand, arthralgia, and autoantibodies which are insufficient to make a diagnosis of a specific CTD category.