Baseline characteristics and 6-month survival of patients included in seasonal and geographical analysis, stratified by myositis-specific autoantibodies
| Variables | Seasonal analysis (n=365) | Geographical analysis (n=481) | ||||||
|---|---|---|---|---|---|---|---|---|
| Anti-MDA5 (n=166) | Anti-ARS (n=120) | Anti-MDA5-/ARS- negative (n=79) | P value | Anti-MDA5 (n=200) | Anti-ARS (n=164) | Anti-MDA5-/ARS-negative (n=117) | P value | |
| Demographics | ||||||||
| Age at onset, years | 55 [29–78] | 59 [29–78] | 63 [33–84] | <0.01 | 56 [30–80] | 56 [27–78] | 61 [30–83] | 0.01 |
| Male | 64 (39%) | 35 (29%) | 30 (38%) | 0.22 | 70 (35%) | 45 (27%) | 46 (39%) | 0.10 |
| Disease duration, months | 2 [0–12] | 3 [0–23] | 3 [0–21] | <0.01 | 2 [0–21] | 3 [0–95] | 3 [0–73] | <0.01 |
| Initial symptoms | ||||||||
| Skin eruption | 93 (56%) | 16 (13%) | 36 (46%) | <0.01 | 112 (56%) | 21 (13%) | 48 (41%) | <0.01 |
| Respiratory symptoms | 34 (20%) | 62 (52%) | 15 (19%) | <0.01 | 41 (21%) | 79 (48%) | 28 (24%) | <0.01 |
| Fever | 21 (13%) | 13 (11%) | 10 (13%) | 0.91 | 24 (12%) | 19 (12%) | 12 (10%) | 0.92 |
| Arthralgia | 12 (7%) | 9 (8%) | 3 (4%) | 0.56 | 11 (6%) | 12 (7%) | 6 (5%) | 0.74 |
| Muscle symptoms | 4 (2%) | 8 (7%) | 12 (15%) | <0.01 | 6 (3%) | 15 (9%) | 16 (14%) | <0.01 |
| Others | 2 (1%) | 12 (10%) | 3 (4%) | <0.01 | 6 (3%) | 18 (11%) | 7 (6%) | 0.01 |
| Diagnosis | ||||||||
| PM | 2 (1%) | 28 (23%) | 15 (19%) | <0.01 | 2 (1%) | 45 (27%) | 28 (24%) | <0.01 |
| Classic DM | 32 (19%) | 46 (38%) | 36 (46%) | 43 (22%) | 63 (38%) | 47 (40%) | ||
| CADM | 132 (80%) | 46 (38%) | 28 (35%) | 155 (78%) | 56 (34%) | 42 (36%) | ||
| Serum biomarkers | ||||||||
| CRP, mg/dL | 1.0 [0.0–5.6] | 0.8 [0.0–21.6] | 0.4 [0.0–26.3] | 0.08 | 0.9 [0.0–5.7] | 0.8 [0.0–20.1] | 0.4 [0.0–20.3] | 0.02 |
| CK, IU/L | 147 [33–3209] | 419 [31–4142] | 414 [48–7505] | <0.01 | 140 [25–2925] | 410 [32–4165] | 337 [36–9378] | <0.01 |
| KL-6, U/mL | 766 [284–2491] | 954 [202–5074] | 669 [207–10 257] | 0.01 | 757 [263–2402] | 947 [224–5074] | 646 [176–6587] | <0.01 |
| Ferritin, ng/mL | 670 [24–6783] | 223 [10–2386] | 186 [26–4808] | <0.01 | 668 [32–6420] | 191 [11–2278] | 210 [23–3766] | <0.01 |
| 6-month survival rates | 67% | 98% | 96% | <0.01 | 68% | 99% | 97% | <0.01 |
Continuous variables are shown as the median [2.5–97.5 percentile]. Categorical variables are shown as n (%). The p-value for diagnosis was calculated by Fisher’s exact test for a 3×3 table. Disease duration means duration from symptom onset to disease diagnosis. Initial symptoms were classified into skin eruption (ie, specific and non-specific skin lesions, and itch), respiratory symptoms (ie, cough and dyspnoea), fever, joint symptoms (ie, arthritis and arthralgia), muscle symptoms (ie, weakness and myalgia) and others. Six-month survival was calculated by the Kaplan–Meier method.
ARS, aminoacyl tRNA synthetase; CADM, clinically amyopathic dermatomyositis; CK, creatine kinase; CRP, C reactive protein; DM, dermatomyositis; KL-6, Krebs von den Lungen-6; MDA5, melanoma differentiation-associated gene 5; PM, polymyositis.