Table 1.
Comparison of baseline characteristics in the derivation, internal and external validation cohorts
| Characteristics | Pittsburgh Derivation cohort (n=260) |
Pittsburgh Validation cohort (n=127) |
Royal Free Validation cohort (n=110) |
p-value | |
|---|---|---|---|---|---|
| Demographics | |||||
| Mean age in years at the first visit (±SD) | 50.5 ± 13.2 | 50.9 ± 13.3 | 51.2 ± 12.4 | 0.95 | |
| Gender (female) | 195 (75%) | 97 (76%) | (74%) | 0.30 | |
| History | |||||
| Disease duration at first visit in years (IQR) | 0.97 (0.68, 1.33) |
0.88 (0.64, 1.31) |
1.02 (0.78, 1.49) |
0.19 | |
| Hypertension | 11 (4%) | 10 (8%) | 4 (4%) | 0.23 | |
| Coronary artery disease | 4 (2%) | 1 (1%) | 2 (2%) | 0.77 | |
| Diabetes mellitus | 6 (2%) | 8 (6%) | 0 (0%) | 0.01 | |
| Overlapping connective tissue disease | 9 (3%) | 4 (3%) | 11 (10%) | 0.02 | |
| Tobacco use: | none | 125 (48%) | 68 (54%) | 23 (21%)* | 0.01 |
| prior use | 94 (36%) | 38 (30%) | 11 (10%) | ||
| current use | 41 (16%) | 20 (16%) | 19 (17%) | ||
| Physical examination findings | |||||
| Mean modified Rodnan skin score (SD) | 26.8 ± 11.9 | 25.2 ± 11.1 | 26.6 ± 8.1 | 0.40 | |
| Skin thickness progression rate slow(<25) | 79 (31%) | 43 (34%) | 39 (35%) | 0.74 | |
| intermediate (25–45) | 91 (35%) | 36 (29%) | 37 (34%) | ||
| rapid (>45) | 90 (35%) | 47 (37%) | 34 (31%) | ||
| Tendon friction rubs (present or absent) | 154 (59%) | 67 (53%) | 27(21%)* | <0.001 | |
| Number of tendon friction rubs | 0 | 101 (39%) | 58 (46%) | 83 (79%) | 0.30 |
| 1–3 | 79 (30%) | 40 (32%) | 15 (14%) | ||
| > 3 | 80 (31%) | 28(22%) | 7 (6%) | ||
| Mean body mass index | 23.9 ± 4.1 | 24.7 ± 4.0 | ---- | ---- | |
| Internal organ system involvement | |||||
| Pulmonary | 70 (27%) | 39 (31%) | 34 (29%) | 0.64 | |
| Renal crisis | 47 (18%) | 15 (12)% | 17 (16%) | 0.28 | |
| Cardiac | 60 (23%) | 21 (17%) | ---- | ---- | |
| Gastrointestinal | 133 (51%) | 70 (56%) | 57 (50%) | 0.76 | |
| Skeletal muscle | 17 (7%) | 11 (9%) | 5 (4.5%) | 0.45 | |
| Pulmonary hypertension | 3 (1%) | 0 | 0 | 0.25 | |
| Laboratory findings | |||||
| Anti-topoisomerase I antibody | 56 (22%) | 34 (28%) | 28 (27%) | 0.47 | |
| Anti-RNA polymerase III antibody | 147 (63%) | 58 (52%) | 66 (61%) | 0.06 | |
| Elevated erythrocyte sedimentation rate‡ | 113 54%) | 45 (54%) | 82 (74%) | <0.001 | |
| Anemia† | 115 (56%) | 61 (49%) | 42 (38%) | 0.31 | |
*
43% missing data for tobacco use;
‡
defined as ESR > (age + 10)/2 for females; ESR > (age/2) for males
□
calculation does not include arrythmia
†
defined as hgb <12 mg/dL