Table 1.
Baseline characteristics of included studies*
| Study | Location | Design | Number (n) | Age at inclusion (years) | Gender (male) (n (%)) | Smoking (n (%)) | Proportion of ILD (n (%))† | Disease duration (RA) (years) | Disease activity‡ | Other CTDs (n) | ILD patterns (on HRCT) (n) |
| Alunno et al 201838 | Italy | Cross-sectional | 252 | 61.7±0.8 | 56 (22.2) | – | 37 (20.2) (n=183) | 12.6±0.6 | – | – | – |
| England et al 201939 | USA | Cross-sectional§ | 1823 | 63.5±11.0 | (90.1) | (89.5) | 90 (4.9) | 11.1±11.5 | 4.0±1.6 | – | – |
| Giles et al 201440 | USA | Cross-sectional§ | 177 | 59±8¶ | 71 (40.1) | 105 (59.3) | 120 (67.8) | 9 (5–19) vs 8 (4–16)¶ | 3.7 (2.9–4.4)¶ (CRP) | – | – |
| Chen et al 201341 | China | Cross-sectional | 103 | 49.1±14.7 | 27 (26.2) | 2 (1.9) | 63 (61.2) | 4.3±5.7 | 4.4±1.4 | – | – |
| Chen et al 201542 | China | Cross-sectional | 71 | 60.7±12.1** | 37 (52.1) | 35 (49.3) | 49 (69.0) | 12.8±10.3 vs 8.4±8.1 (n=68) | 3.7±1.2 vs 3.3±1.7 (n=43) | – | – |
| Doyle et al 201543 | USA | Cross-sectional§ | 75 | 61.5±12.7** | 11 (14.7) | 41 (54.7) | – | – | – | – | – |
| Abdel-Hamid et al 201944 | Egypt | Cross-sectional | 50 | 45.8±12.3 | 2 (4.0) | – | 19 (38.0) | 9.8±6.6 | 4.7±1.3 | 0 | – |
| Akiyama et al 201645 | Japan | Cross-sectional | 395 | 58.5±13.1 | 49 (12.4) | 69 (20.3) (n=340) | 78 (19.7) | 129.4±115.2 (months) | 4.9±1.6 (n=372) | 38 (SS, SSc, PM/DM, SLE) | – |
| Alexiou et al 200846 | Greece | Case–control | 136 | – | – | – | N/A (ILD 11/no ILD 125) | – | – | – | – |
| Correia et al 201947 | USA | Cross-sectional | 453 | 59.6±15.7 | (19.4) | – | (6.0) | – | – | 0 | – |
| Fadda et al 201848 | Egypt | Cross-sectional | 88 | 50.2±9.0 | 13 (14.8) | 87 (98.9) | 63 (71.6) | 10.2±6.2 | 14 (1–32) vs 12 (3–25) (median (range)) (CDAI) | 0 | UIP 62%, NSIP 27%, Mixed 1% |
| Furukawa et al 201249 | Japan | Case–control | 450 | 63.9±10.9** | 89 (19.8) | 130 (28.9) | N/A (ILD 129/no ILD 321) | 14.5±10.9** | – | – | – |
| Kakutani et al 201950 | Japan | Cross-sectional | 2702 | 62.8±12.5 | (17.8) | (28.9) | 261 (9.7) | 9 (15) vs 10 (17) (median (IQR)) | 3.2±1.0 (ESR) | – | – |
| Kelly et al 201451 | UK | Case–control | 460 | – | 220 (47.8) | – | N/A (ILD 230/no ILD 230) | – | – | – | – |
| Liu et al 201952 | China | Cross-sectional | 101 | 54 (17) (median (IQR)) | 26 (25.7) | – | 23 (22.8) | 7 (14) (median (IQR) | 4.0±1.9 | – | – |
| Matsuo et al 201853 | Japan | Cross-sectional | 312 | 63.5±12.7 | 41 (13.1) | 95 (30.4) | 26 (8.3) | 14.9±11.6 | 2.5±1.1 (CRP) | 11 (not specified) | – |
| Mori et al 201254 | Japan | Cross-sectional | 356 | 72.5 (12.3) (n=24) vs 59.0 (16) (n=302) (median (IQR)) | 85 (23.9) | 76 (21.3) | 24 (6.7) | 1.5 (6.3) (n=24) vs 0 (6) (n=302) (median (IQR)) | – | – | UIP 5, NSIP 19 |
| Ortancil et al 201155 | Turkey | Cross-sectional | 67 | 57.4±13.5 | 14 (20.9) | – | 12 (17.9) | 10.2±11.7** | – | – | – |
| Park et al 201656 | Korea | Cross-sectional | 83 | 53.7±10.1** | 10 (12.0) | – | 7 (8.4) | – | – | – | UIP 6, indeterminate 1 |
| Paulin et al 201957 | Argentina | Case–control | 118 | 56.7±15.7 | 26 (22.0) | 52 (44.1) | N/A (ILD 52/no ILD 66) | 6 (8) (median (IQR)) | 3.4±1.1 | – | – |
| Restrepo et al 201558 | USA | Cross-sectional | 779 | 53.7±13.3 (n=632)** | 161 (25.5) (n=632) | 357 (56.5) (n=632) | 69 (8.9) | 10.5±10.3¶ | 5.4±1.4** | – | – |
| Rocha-Munoz et al 201559 | Mexico | Case–control | 81 | 51.0 (36.0–72.0) vs 49.0 (24.0–73.0) (median (range)) | – | 22 (27.2) | N/A (ILD 39/no ILD 42) | 7.0 (1.0–35.0) vs 6.5 (0.75–25.0) (median (range)) | 3.9 (1.7–5.3) vs 2.5 (1.7–5.1) (median (range)) | 0 | – |
| Sargin et al 201860 | Turkey | Cross-sectional | 83 | 59.3±12.1 | 20 (24.1) | 9 (10.8) | 43 (51.8) | – | – | 0 | – |
| Sulaiman et al 201961 | Malaysia | Cross-sectional | 159 | 48.3±14.1 | 25 (15.7) | – | 21 (13.2) | – | 4.7±0.9 (ESR) | 0 | – |
| Tian et al 201662 | China | Cross-sectional | 75 | – | 29 (38.7) | – | 37 (49.3) | – | – | – | – |
| Wang et al 201563 | China | Cross-sectional | 41 | 60.7±12.4** | 20 (48.8) | – | 25 (61.0) | 108 (5–360) vs 72 (2–552) (months) (median (range)) | – | – | – |
| Yang et al 201964 | Korea | Case–control | 308 | 57.0±12.0** | 76 (24.7) | 39 (17.7) (n=220) | N/A (ILD 77/no ILD 231) | 11.0±7.3** | – | – | – |
| Yin et al 201465 | China | Cross-sectional | 285 | 51.7±13.4** | 74 (26.0) | 59 (20.7) | 71 (24.9) | 9.0 (16.0) vs 4.0 (9.1) (median (IQR)) | 5.4±1.7 | 61 (SS 41, SSc 7, PM/DM 4, SLE 16)†† | – |
| Zhang et al 201866 | China | Case–control | 75 | 41–69 vs 40–70 (range) | 30 (40.0) | – | N/A (ILD 28/no ILD 47) | – | – | 0 | – |
*Comparisons correspond to RA-ILD vs RA without ILD and the values are expressed as mean±SD or number (proportion) unless otherwise specified.
†N/A indicates not applicable due to case–control studies.
‡Disease activity was estimated using disease activity score (DAS) 28 unless otherwise specified and a laboratory marker used to calculate the score was described as either ESR or CRP if it was specified.
§A prospective study while all of the other studies were retrospectively designed.
¶Unknown statistics.
**Calculated combining the figure in both comparative groups.
††Some patients had multiple CTDs.
CDAI, clinical disease activity index; CRP, C-reactive protein; CTD, connective tissue disease; ESR, erythrocyte sedimentation rate; HRCT, high-resolution CT; ILD, interstitial lung disease; NSIP, non-specific interstitial pneumonia; PM/DM, polymyositis/dermatomyositis; RA, rheumatoid arthritis; SLE, systemic lupus erythematosus; SS, Sjögren syndrome; SSc, systemic sclerosis; UIP, usual interstitial pneumonia.;