Table 1.
Demographics and diagnostic features (N = 119)
| Age at diagnosis in years, median (IQR) | 8 (4.0–11.5) |
| Age at disease onset in years, median (IQR) | 7 (3.5–7.5) |
| Time to diagnosis in months, median (IQR) | 3 (1–6.5) |
| Female, N (%) | 76 (63.4) |
| Race or Ethnicitya, N (%) | |
| White | 86 (72.3) |
| Hispanic, Latino, or Spanish origin | 22 (18.5) |
| Black, African American, African, or Afro-Caribbean | 9(7.6) |
| Asian | 7(5.9) |
| Native American, American Indian or Alaskan Native | 3 (2.5) |
| Middle Eastern | 3 (2.5) |
| Unknownb | 3 (2.5) |
| Otherc | 4 (3.4) |
| Concomitant Medical History, N (%)d | 22 (16.8) |
| Family History of Autoimmunity, N (%)e | 25 (21) |
| Skin Predominant JDM, N (%) | 38 (31.9) |
| History of, N (%) | |
| Proximal Muscle Weakness | 86 (72.3) |
| Rash (Heliotrope or Gottron’s) | 110 (92.4) |
| Elevated muscle enzymes | 99 (83.2) |
| EMG performed | 4 (3.4) |
| Muscle Biopsy performed | 19 (16) |
| MRI performed | 81 (68.1) |
| Autoantibodies, proportionf | |
| ANA | 75/96 (78.1%) |
| Myositis-specific antibodies | |
| Anti-MJ/NXP2 | 11/49 (22.4%) |
| Anti-p155/140/TIF1-𝛄 | 7/53 (13.2%) |
| Anti-Mi2 | 6/55 (10.9%) |
| Anti-MDA5 | 4/51 (7.8%) |
| Anti-Jo1 | 2/67 (3.0%) |
| Myositis-associated antibodies | |
| Anti-PM-Scl | 3/43 (7.0%) |
| Anti-Smith | 1/56 (1.7%) |
aSome participants reported more than one Race and/or Ethnicity
bPatient/guardian chose “other” and/or “not any of the Races”
cPatient/guardian chose “prefer not to answer” and/or did not provide a responsed
dTwenty-two of the enrolled participants had a history of at least one other medical condition: 5 participants had a history of asthma, 3 autoimmune thyroid disease, 1 celiac disease, 2 other autoimmune disease, and 12 other major or or acquired disease. One participant had a history of multiple autoimmune conditions including thyroid, celiac, and other autoimmune disease in addition to JDM
eTwenty-five participants had a history of autoimmunity in first-degree family members, and 5 of these participants had a family history of more than one autoimmune condition. The most common condition was psoriasis in 9 family members, followed by rheumatoid arthritis in 4, systemic lupus erythematosus in 3, inflammatory bowel disease in 3, autoimmune thyroid disease in 3, ankylosing spondylitis in 2, celiac disease in 2, juvenile arthritis in 1, Sjogren’s disease in 1, and other autoimmune disease in 4
fProportion of patients with a positive test of the total number tested