Demographics of study populations
| Patients with IIM | Controls | |||
| N | 1644 | 3526 | ||
| Sex, F: M | 0.668 : 0.332 | 0.730 : 0.270 | ||
| Age at disease diagnosis or recruitment (controls), years old | 50.5±16.3 | 62.5±6.2 | ||
| Sources | n | n | n (total) | |
| Belgium | 36 | – | 36 | |
| Czech Republic | 329 | 96 | 425 | |
| UK | 760 | 1451 | 2211 | |
| USA | 138 | 945 | 1083 | |
| Sweden | 381 | 1034 | 1415 | |
| Total | 1644 | 3526 | 5170 | |
| Subgroups of patients with IIM, n (%)* | ||||
| F | M | Total | F/M | |
| DM | 391 (69.3) | 173 (30.7) | 564 | 2.26 |
| PM | 473 (71.2) | 191 (28.8) | 664 | 2.48 |
| IBM | 75 (41.7) | 105 (58.3) | 180 | 0.71 |
| JDM | 103 (67.3) | 50 (32.7) | 153 | 2.06 |
| Overall | 1042 | 519 | 1561* | (2.01) |
| Age at diagnosis (years old) | MSA+, % | MAA+, % | ||
| DM | 49.2±15.0 | 65.4 | 28.7 | |
| PM | 50.4±14.2 | 42.7 | 38.6 | |
| IBM | 61.2±9.3 | 2.4 | 19.3 | |
| JDM | 7.9±4.3 | 42.9 | 22.7 | |
*The patient population with IIM also included 28 patients diagnosed with immune-mediated necrotising myositis, 24 patients with anti-synthetase syndrome, 19 patients with unspecified subcategory of disease, plus 12 patients with gender unknown.
DM, dermatomyositis; IBM, inclusion body myositis; IIM, idiopathic inflammatory myopathies; JDM, juvenile dermatomyositis; MAA, myositis-associated autoantibodies; MSA, myositis-specific autoantibodies; PM, polymyositis.