Myositis-specific autoantibodies in Japanese patients with juvenile idiopathic inflammatory myopathies

The aim of our study is to clarify the association of myositis-specific autoantibodies (MSAs) with clinical and laboratory features in Japanese patients with juvenile idiopathic inflammatory myopathies (JIIMs).

We retrospectively analyzed the frequency of MSAs and their association with clinical or laboratory findings in 25 Japanese patients with JIIMs in Hokkaido district.

Eighteen of the 25 patients (72%) were positive for MSAs; seven with anti-melanoma differentiation associated gene (MDA) 5 (28%), five with anti-transcriptional intermediary factor (TIF)-1γ (20%), four with anti-MJ/nuclear matrix protein (NXP)-2 (16%), two with anti-Jo-1 (8%), one with anti- HMG-CoA reductase, one with anti-signal recognition peptide (SRP) antibodies (4% each), including co-existence and transition of MSAs in one patient each. Anti-MDA5 antibodies were related to interstitial lung disease (ILD) and arthritis but not to amyopathic juvenile dermatomyositis. Drug-free remission was achieved, once ILD was overcome in this group. Anti-TIF-1γ antibodies were associated with typical rashes and mild myositis. Anti-MJ/NXP2 and anti-SRP antibodies were associated with severe muscle weakness. No patient was complicated with malignancy.

Anti-MDA5 antibodies are prevalent and closely associated with ILD in our series compared with other countries. There was no apparent difference in clinical features associated with other MSAs among races.