[Comparison of clinical and immunological features between clinically amyopathic dermatomyositis and typical...

To study the differences between clinically amyopathic dermatomyositis (CADM) and typical dermatomyositis (DM) on clinical and immunological features.

By collecting clinical data of 106 CADM patients and 158 DM patients from January 2010 to June 2019 in the department of Rheumatology and Immunology, Peking University People's Hospital, the clinical characteristics and immunological features in the two groups were compared, and the distribution characters and the clinical meanings of myositis autoantibodies were discussed in the two groups respectively. Myositis autoantibodies were measured by immunoblotting according to the manufacturers' instructions.

In the aspects of clinical manifestations, CADM presented more with onset of interstial lung diseases (ILD) compared with DM (20.7% vs. 7.6%, P=0.002), and CADM-ILD was more likely to be acute ILD (58.3% vs. 26%, P < 0.001), and there were no differences between CADM and DM in cutaneous manifestations, accompanied with connective tissue disease (CTD) and malignancy. In CADM, the positive rate of rheumatoid factors and antinuclear antibodies was lower in DM. The most common myositis specific autoantibodies (MSAs) in CADM were anti-MDA5 (36%), anti-PL-7 (11.2%) and anti-TIF-1γ (10.1%). The most common MSAs in DM were anti-Jo-1 (19.2%), anti-TIF-1γ (11.5%) and anti-MDA5 (11.5%). Anti-MDA5 was correlated with acute ILD and skin ulceration both in CADM and DM; in CADM, skin ulceration was not associated with the titer of anti-MDA5; while in DM, skin ulceration was associated with high titer of anti-MDA5. In DM, anti-TIF-1γ was correlated with heliotrope eruption, V/shawl neck sign, perionychia erythma and malignancy, and higher rate of malignancy was seen in all titers of the anti-TIF-1γ positive patients. In CADM, anti-TIF1-γ showed no correlation with clinical manifestations. The most common myositis associated autoantibody was anti-Ro-52 both in CADM and DM. In CADM, anti-Ro-52 was associated with Raynaud's phenomenon and chronic ILD, while in DM, anti-Ro-52 was associated with mechanic's hands, noninfectious fever and accompanied CTD.

Compared with DM, ILD is more likely to be acute in CADM. It is different between CADM and DM about the distribution of myositis autoantibodies and the clinical significance of the same myositis antibody, and the clinical significance of some myositis antibodies is related to titers.