Clinical characteristics of the patients in the IIM subgroups and the non-IIM group
| DM (n=36) | ADM (n=17) | PM (n=19) | Non-IIM* (n=16) | p<0.05 | |
| Age (years), mean (SD) | 53.5 (14.3) | 50.5 (11.7) | 64.1 (11.4) | 54.6 (15.8) | DM versus PM ADM versus PM |
| Female, n (%) | 24 (66.7) | 8 (47.1) | 12 (63.2) | 11 (68.8) | NSD |
| Muscle weakness, n (%) | 34 (94.4) | 2 (11.8) | 15 (79.0) | 10 (62.5) | DM versus ADM DM versus non-IIM ADM versus PM ADM versus non-IIM |
| Myalgia, n (%) | 24 (66.7) | 11 (64.7) | 8 (42.1) | 8 (50.0) | NSD |
| CK level (IU/litre), mean (SD) | 1771.9 (2557.8) | 394.6 (586.9) | 1840.1 (1651.4) | 1423.1 (1456.7) | DM versus ADM ADM versus PM ADM versus non-IIM |
| Time from onset of symptoms to first MRI (days), mean (SD) | 157.9 (243.6) | 205.4 (394.6) | 495.6 (622.0) | 454.4 (711.5) | DM versus PM |
| Muscle biopsy performed, n (%) | 29 (80.6) | 10 (58.8) | 15 (78.9) | 9 (86.7)† | NSD |
| Inflammatory cell infiltration in muscle, n (%) | 25 (86.2) | 7 (70.0) | 15 (100.0) | 9 (100.0) | NSD |
*Non-IIM included anti-ARS antibody-positive myositis (n=4), definite or probable PM by the Bohan and Peter criteria (n=4), anti-mitochondrial antibody-positive myositis (n=3), SLE (n=2), SSc (n=2) and MCTD (n=1).
†Muscle biopsy was performed in nine patients with non-IIM: anti-ARS antibody-positive myositis (n=2), definite or probable PM by the Bohan and Peter criteria (n=3), anti-mitochondrial antibody-positive myositis (n=2), SLE (n=1), SSc (n=1).
ADM, amyopathic dermatomyositis;ARS, aminoacyl-tRNA synthetases;CK, creatine kinase;DM, dermatomyositis;IIM, idiopathic inflammatory myopathy;MCTD, mixed connective tissue disease; NSD, no significant differences among the subgroups;PM, polymyositis;SLE, systemic lupus erythematosus;SSc, systemic sclerosis.