Demographic data of the International Myositis Classification Criteria Project cohort
| IIM (n=976) | Comparators (n=624) | |
| Sex, n (%) | ||
| Female | 652 (66.8) | 369 (59.1) |
| Male | 324 (33.2) | 255 (40.9) |
| Adult onset disease*, n (%) | 727 (74.5) | 509 (81.6) |
| Childhood onset disease*, n (%) | 249 (25.5) | 115 (18.4) |
| Age at onset of symptoms, median (IQR), years | 44.0 (14.7–57.0) | 41.0 (20.0–56.0) |
| Age at diagnosis, median (IQR), years | 45.5 (16.2–59.3) | 45.0 (25.8–58.0) |
| Disease duration from time of first symptom†, median (IQR), years | 4.0 (2.0–8.0) | 4.0 (1.0–9.0) |
| Disease duration from time of diagnosis‡, median (IQR), years | 3.0 (1.0–6.0) | 1.8 (0.0–4.5) |
| Ethnicity, n (%) | ||
| Caucasian | 611 (62.6) | 360 (57.7) |
| Asian | 177 (18.1) | 156 (25.0) |
| Hispanic | 51 (5.2) | 25 (4.0) |
| African | 40 (4.1) | 28 (4.5) |
| Native American | 18 (1.8) | 4 (0.6) |
| Pacific Islander | 3 (0.3) | 1 (0.2) |
| Mixed | 37 (3.8) | 22 (3.5) |
| Unknown | 54 (5.5) | 32 (5.1) |
| Disease onset§, n (%) | ||
| Acute (days to 2 weeks) | 45 (4.6) | 64 (10.3) |
| Subacute (>2 weeks to ≤2 months) | 237 (24.3) | 88 (14.1) |
| Insidious (>2 months to years) | 648 (66.4) | 444 (71.2) |
| NA | 46 (4.7) | 28 (4.5) |
*Onset of first symptoms assumed to be related to the disease.
†Time from first symptom to last clinical evaluation.
‡Time from diagnosis to last clinical evaluation.
§Onset and progression of the first symptoms of the syndrome to the full disease presentation.
IIM, idiopathic inflammatory myopathies; NA, information not available.