Table 1.
Baseline characteristics of the juvenile dermatomyositis patients from the discovery and validation cohorts*
| Discovery cohort (Chicago, IL) (n = 30) | Validation cohort (Netherlands and Singapore) (n = 25 and n = 4) | P | |
|---|---|---|---|
| Age at sampling, median (IQR) years | 5.1 (3.7–8.6) | 7 (3.9–12.1) | 0.192 |
| Sex, no. (%) female | 26 (86.7) | 18 (62.1) | 0.039 |
| Ethnicity, % white/Hispanic/African American/Asian | 77/20/3/0 | 76/0/10/14 | 0.012 |
| Duration of untreated disease, median (IQR) months | 5.9 (3.6–14.8) | 3.2 (1.4–9.1) | 0.020 |
| Intensification of treatment in first 3 months, no. (%) | 17 (56.7) | 8 (28.6) | 0.038 |
| Disease activity at diagnosis | |||
| CMAS (scale 0–52 or 0–49 for ages 4–5 years), median (IQR) | 33 (23.5–44)† | 33 (15–40.5)‡ | 0.334 |
| PhGA, median (IQR) (scale 0–10) | – | 5.8 (4.0–7.7)‡ | NA |
| DAS total, median (IQR) (scale 0–20) | 12 (9.4–13.3) | – | NA |
| DAS muscle, median (IQR) (scale 0–11) | 6 (3.8–8) | – | NA |
| DAS skin, median (IQR) (scale 0–9) | 5 (5–6.3) | – | NA |
| CAT score, median (IQR) (scale 0–116) | – | 5 (3.5–11) | NA |
| Muscle enzyme levels at diagnosis, median (IQR) IU/liter | |||
| CK | 131 (88–680) | 510 (138–4,357) | 0.053 |
| LDH | 364 (270–460)† | 497 (358–837)‡ | 0.010 |
| AST | 46 (35–80) | 65 (41–307)§ | 0.118 |
| ALT | 26 (17–43)† | 45 (23–112) | 0.158 |
| Myositis‐specific antibodies, no. (%) | |||
| Negative | 14 (46.7) | 16 (55.2) | 0.800 |
| MDA‐5 | 2 (6.7) | 2 (6.9) | 1.000 |
| Mi‐2 | 3 (10) | 0 (0) | 0.237 |
| NXP‐2 | |||
| Total | 2 (6.7) | 5 (17.2) | 0.254 |
| Strongly positive | 1 (3.3) | 3 (10.3) | |
| Weakly positive | 1 (3.3) | 2 (6.9) | |
| SAE‐1 | 0 (0) | 2 (6.9) | 0.237 |
| TIF‐1γ | |||
| Total | 9 (30.0) | 4 (13.8) | 0.209 |
| TIF‐1γ only | 8 (26.7) | 3 (10.3) | |
| TIF‐1γ + PL‐7 | 0 (0) | 1 (3.4) | |
| TIF‐1γ + PL‐12 | 1 (3.3) | 0 (0) | |
| Initial therapy after diagnosis, no. (%) | |||
| Oral Pred. | 1 (3.3) | 0 (0.0) | 1.000 |
| MTX + oral Pred. | 2 (6.7) | 0 (0.0) | 0.492 |
| IVMP + oral Pred. | 1 (3.3) | 1 (3.4) | 1.000 |
| IVMP + oral Pred. + MTX | 19 (63.3) | 20 (69.0) | 0.7847 |
| IVMP + oral Pred. + IVIG | 0 (0.0) | 1 (3.4) | 0.492 |
| IVMP + oral Pred. + MTX + IVIG | 1 (3.3) | 0 (0.0) | 1.000 |
| IVMP + oral Pred. + MTX + HCQ | 6 (20.0) | 7 (24.1) | 0.761 |
P values were calculated by Mann‐Whitney U test for continuous variables, and by Fisher's exact test for categorical variables (comparisons of 2 categories) or chi‐square test (comparisons of >2 categories). Myositis‐specific antibodies were measured by line blot assay. Normalization of muscle enzyme levels to the age‐ and center‐specific upper limits of normal did not change the results. IQR = interquartile range; CMAS = Childhood Myositis Assessment Scale; PhGA = physician's global assessment of disease activity; NA = not applicable; DAS = Disease Activity Score; CAT = cutaneous assessment tool (for juvenile dermatomyositis); CK = creatine kinase; LDH = lactate dehydrogenase; AST = aspartate aminotransferase; ALT = alanine aminotransferase; MDA‐5 = melanoma differentiation–associated protein; NXP‐2 = nuclear matrix protein 2; SAE‐1 = small ubiquitin‐like modifier‐1 activating enzyme; TIF‐1γ = transcription intermediary factor 1γ; Pred. = prednisone; MTX = methotrexate; IVMP = intravenous methylprednisolone; IVIG = intravenous immunoglobulin; HCQ = hydroxychloroquine.
Data not reported for 1 patient.
Data not reported for 4 patients.
Data not reported for 2 patients.