Baseline characteristics of study participants
Participants’ baseline characteristics are listed in Table 1. Finally, 124 patients (32 men, 92 women) were included. The median age was 70.0 (IQR 59.0, 75.0) years, and the median disease duration was 2.92 (IQR 1.40, 8.75) years. Seventy-five (60.9%) were RF positive and 62 (50.4%) were anti-CCP antibody positive, and 36 (29.0%) were ANA positive. The median RF titre was 28 U/mL (IQR 5, 139), and the median anti-CCP antibody titre was 4.6 U/mL (IQR 0.5, 165.9). The median values of DAS28-ESR were 2.34 (IQR 1.54, 3.36). Pulmonary function tests were available for 83 participants, and the median value of FVC% predicted was 100.8% (IQR 91.2%, 112.0%). According to HRCT assessment, 17 was classified as having ILD and 16 (12.9%) showed RA-associated bronchial disease (bronchiolitis or bronchiectasis). At registration, the proportion of patients receiving concomitant medications was as follows: glucocorticoids 45.1%, methotrexate 62.9%, tumor necrosis factor inhibitors 8.8%, interleukin-6 inhibitors 20.1%, abatacept 4.8% and Janus kinase (JAK) inhibitors 12.1%.
Table 1
Characteristics of the patients
| Total (n = 124) |
Demographics | |
Age (years), median (IQR) | 70.0 (59.0, 75.0) |
Male, n (%) | 32 (25.8%) |
Disease duration (years), median (IQR) | 2.92 (1.40, 8.75) |
Ever smoker, n (%) | 46 (37.1%) |
mMRC, 0 / 1 / 2 / 3 / 4, n | 90 / 23 / 4 / 6 / 1 |
Cough, present, n (%) | 25 (18.6%) |
Steinbrocker stage Ⅰ / Ⅱ / Ⅲ / Ⅳ | 91 / 9 / 8 / 15 |
Steinbrocker stage ≥Ⅱ | 32 (25.8%) |
Laboratory data | |
WBC (/µL), median (IQR) | 5640.0 (4438.0, 7575.0) |
Lymphocyte (/µL), median (IQR) | 1420.0 (1017.0, 1797.0) |
Haemoglobin (g/dL), median (IQR) | 13.2 (12.4, 14.2) |
LDH (U/L), median (IQR) | 202.5 (178.5, 238.5) |
ALP (U/L), median (IQR) | 74.0 (61.0, 92.0) |
KL-6 (IU/mL), median (IQR) | 230.0 (180.8, 326.8) |
SP-D (ng/mL), median (IQR) | 67.1 (45.3, 98.9) |
ANA positive (≥1: 80), n (%) | 36 (29.0%) |
Rheumatoid factor, positive, n (%) | 75 (60.9%) |
Rheumatoid factor, titre (U/mL) | 28 [5, 139] |
Anti-CCP antibody, positive, n (%) | 62 (50.4%) |
Anti-CCP antibody, titre (U/mL) | 4.6 [0.5, 165.9] |
DAS28-ESR, median (IQR) | 2.34 (1.54, 3.36) |
Pulmonary function tests, n | n = 83 |
Forced vital capacity (L), median (IQR) | 2.65 (2.22, 3.07) |
Forced vital capacity percent predicted (%), median (IQR) | 100.8 (91.2, 112.0) |
HRCT assessment | |
ILD present, n (%) | 17 (13.7%) |
Treatment | |
Glucocorticoids, n (%) | 56 (45.1%) |
Methotrexate, n (%) | 78 (62.9%) |
bDMARDs, n (%) | 43 (34.6%) |
TNF inhibitors, n (%) | 11 (8.8%) |
IL-6 inhibitors, n (%) | 25 (20.1%) |
Abatacept, n (%) | 6 (4.8%) |
JAK inhibitors, n (%) | 15 (12.1%) |
a mixed connective tissue disease: n = 1, dermatomyositis: n = 1. |
Abbreviations: ALP, alkaline phosphatase; ANA, antinuclear antibody; Anti-CCP antibody, anti-cyclic citrullinated peptide antibody; bDMARDs, biological disease-modifying anti-rheumatic drugs; CDAI, clinical disease activity index; CTD, connective tissue disease; DAS28-ESR, disease activity score 28-erythrocyte sedimentation rate; HRCT, high-resolution computed tomography; IQR, interquartile range; IL-6, interleukin-6; ILD, interstitial lung disease; JAK inhibitors, Janus kinase inhibitors; KL-6, Krebs von den Lungen-6 antigen; LDH, lactate dehydrogenase; mMRC, modified Medical Research Council dyspnoea scale; SP-D, surfactant-associated protein D; SSc, systemic sclerosis; TNF inhibitors, tumour necrosis factor inhibitors; WBC, white blood cell |
Patients’ characteristics stratified according to the radiological severity of ILD.
Patients’ characteristics stratified according to the radiological severity of ILD are listed in Table 2. Among 124 patients, 107 (86.2%) had no ILD, nine (7.2%) had ILD with extent < 10%, three (2.4%) had ILD with extent ≥10% and < 20% and five (4.0%) had ILD with extent ≥20%. Among 17 patients (13.7%) diagnosed with ILD based on HRCT assessment, seven (41.1%) were classified as having usual interstitial pneumonia pattern, 9 (52.9%) as having non-specific interstitial pneumonia pattern. No patient was diagnosed with acute exacerbation of RA-ILD at registration. All patients had chronic ILD at registration, and no patient showed subacute change on ILD which suggest organizing pneumonia (OP) or OP superimposed to preexisting ILD. None of the patients with ILD showed RA-associated bronchial disease (bronchitis or bronchiectasis). Inter-reader agreement for ILD extent was ‘nearly perfect’ with κ = 0.896 (P < 0.01) among the 17 patients with ILD. Representative results of the radiological severity of ILD are presented in Fig. 1. Post-stratification, the median values of KL-6 were elevated from 216.0 IU/mL, 345.0 IU/mL, 330.0 U/mL to 949.0 IU/mL in accordance with ILD extent = 0%, ILD extent < 10%, ILD extent ≥10% and < 20% and ILD extent ≥20%, respectively, and the median values of FVC% predicted were decreased from 102.5%, 100.8%, 70.6–80.6% in accordance with ILD extent = 0%, ILD extent < 10%, ILD extent ≥10% and < 20% and ILD extent ≥20%, respectively. The median values of DAS28-ESR were elevated from 2.30, 2,45, 3.19 to 4.47 in accordance with ILD extent = 0%, ILD extent < 10%, ILD extent ≥10% and < 20% and ILD extent ≥20%, respectively.
Table 2
Patient characteristics stratified according to the radiological severity of interstitial lung disease
| No ILD (ILD extent = 0%) (n = 107) | 0%< ILD < 10% (n = 9) | 10%≤ ILD < 20% (n = 3) | ILD ≥20% (n = 5) |
Age, median (IQR) | 69.0 [58.5, 74.0] | 71.0 [70.0, 75.0] | 70.0 [66.0, 76.5] | 73.0 [73.0, 78.0] |
Sex, n (%) | 27 (25.2%) | 2 (22.2%) | 2 (66.6%) | 1 (20.0%) |
Disease duration (years), median (IQR) | 2.82 [1.35, 8.38] | 3.65 [2.18, 5.86] | 9.89 [5.52, 20.86] | 3.29 [2.62, 5.71] |
Ever smoker, n (%) | 39 (36.4%) | 2 (22.2%) | 2 (66.6%) | 3 (60.0%) |
mMRC ≥1 | 24 (22.4%) | 4 (44.4%) | 2 (66.6%) | 4 (80.0%) |
Cough | 14 (13.0%) | 5 (55.5%) | 2 (66.6%) | 4 (80.0%) |
KL-6 (U/mL), median (IQR) | 216.0 [173.5, 294.5] | 345.0 [223.0, 499.0] | 330.0 [296.0, 544.0] | 949.0 [623.0, 979.0] |
SP-D (ng/mL), median (IQR) | 62.9 [42.9, 87.0] | 82.3 [52.6, 110.1] | 85.2 [80.7, 146.4] | 93.6 [91.3, 208.6] |
Rheumatoid factor, titre (U/mL) | 24.0 [5.0, 86.0] | 47.0 [18.0, 127.0] | 318.0 [262.5, 409.0] | 189.0 [157, 500.0] |
Anti-CCP antibody, titre (U/mL) | 2.4 [1.7, 102.2] | 19.1 [1.7, 618.8] | 89.4 [83.7, 169.2] | 865.0 [387.8, 867.5] |
DAS28-ESR, median (IQR) | 2.30 [1.54, 3.30] | 2.45 [1.81, 3.03] | 3.19 [2.40, 4.79] | 4.47 [3.68, 5.17] |
Pulmonary function tests, available, n | n = 66 | n = 9 | n = 3 | n = 5 |
Forced vital capacity (L), median (IQR) | 2.70 [2.24, 3.24] | 2.76 [2.30, 2.92] | 2.40 [2.28, 2.55] | 1.75 [1.66, 2.32] |
Forced vital capacity percent predicted (%), median (IQR) | 102.5 [94.8, 114.2] | 100.8 [95.4, 111.9] | 70.6 [68.3, 89.7] | 80.6 [71.0, 96.3] |
ILD extent (%) | 0.00 [0.00, 0.00] | 5.00 [3.33, 7.50] | 14.17 [12.09, 16.07] | 30.42 [29.59, 43.75] |
Treatment at registration | MTX 63.5%, bDMARDs 36.4%, JAKi 10.2% | MTX 66.6%, bDMARDs 11.1%, JAKi 44.4% | MTX 66.6%, bDMARDs 33.3% | MTX 40.0%, bDMARDs 40.0% |
Abbreviations: bDMARDs, biological disease-modifying anti-rheumatic drugs; IQR, interquartile range; JAK inhibitors, Janus kinase inhibitors; ILD, interstitial lung disease; KL-6, Krebs von den Lungen-6 antigen; mMRC, modified Medical Research Council dyspnoea scale; MTX, methotrexate; |
SP-D, surfactant-associated protein D. |
Factors associated with the quantitative extent of ILD.
Table 3 presents the univariate and multivariate linear regression analysis of the factors associated with the quantitative severity of ILD. DAS28-ESR (standardized coefficient = 0.295, P < 0.01), RF titre (standardized coefficient = 0.318, P < 0.01) and anti-CCP antibody titre (standardized coefficient = 0.184, P = 0.040) were significantly associated with quantitative extent of ILD in univariate analysis. Among these covariates, RF titre (standardized coefficient = 0.247, P = 0.01) and DAS28-ESR (standardized coefficient = 0.199, P = 0.03) were significantly associated with the quantitative extent of ILD in multivariate analysis adjusted for age, male sex, smoking status and anti-CCP antibody titre.
Table 3
Factors associated with the quantitative extent of ILD
| Univariate analysis | | Multivariate analysis | |
| Standardized coefficient (95% CI) | P value | Standardized coefficient (95% CI) | P value |
Age | 0.144 (-0.032, 0.319) | 0.11 | 0.073 (-0.096, 0.243) | 0.39 |
Male sex | -0.001 (-0.178, 0.177) | 0.99 | -0.177 (-0.417, 0.063) | 0.15 |
Disease duration (years) | -0.013 (-0.191, 0.164) | 0.88 | -0.082 (-0.259, 0.096) | 0.36 |
Smoking | 0.092 (-0.084, 0.269) | 0.30 | 0.262 (0.015, 0.509) | 0.03a |
DAS28-ESR | 0.295 (0.126, 0.465) | < 0.01a | 0.199 (0.016, 0.382) | 0.03a |
Rheumatoid factor, titre | 0.318 (0.150, 0.486) | < 0.01a | 0.247 (0.060, 0.435) | 0.01a |
Anti-CCP antibody, titre | 0.184 (0.010, 0.358) | 0.040a | 0.125 (-0.041, 0.290) | 0.14 |
a P < 0.05 |
Abbreviations; anti-CCP antibody, anti-cyclic citrullinated peptide antibody; CI, confidence interval; DAS28-ESR, disease activity score 28-erhythrocyte sedimentation rate; ILD, interstitial lung disease. |
Factors associated with FVC% predicted.
Univariate and multivariate linear regression analysis of the factors associated with the value of FVC% predicted are presented in Table 4. DAS28-ESR (standardized coefficient = -0.342, P < 0.01) and RF titre (standardized coefficient = -0.326, P < 0.01) were significantly associated with FVC% predicted in univariate analysis. DAS28-ESR (standardized coefficient = -0.230, P = 0.047) was significantly associated with FVC% predicted in multivariate analysis adjusted for age, male sex, smoking status, RF titre and anti-CCP antibody titre.
Table 4
Factors associated with forced vital capacity% predicted
| Univariate analysis | | Multivariate analysis | |
| Standardized coefficient (95% CI) | P value | Standardized coefficient (95% CI) | P value |
Age | -0.202 (-0.418, 0.015) | 0.07 | -0.121 (-0.329, 0.087) | 0.25 |
Male sex | -0.175 (-0.403, 0.052) | 0.13 | -0.088 (-0.375, 0.199) | 0.54 |
Disease duration (years) | 0.094 (-0.116, 0.304) | 0.38 | 0.155 (-0.051, 0.361) | 0.14 |
Smoking | -0.134 (-0.349, 0.081) | 0.22 | -0.112 (-0.389, 0.164) | 0.42 |
DAS28-ESR | -0.342 (-0.530, -0.154) | < 0.01a | -0.230 (-0.453, -0.006) | 0.047a |
Rheumatoid factor, titre | -0.326 (-0.528, -0.135) | < 0.01a | -0.229 (-0.459, 0.002) | 0.055 |
Anti-CCP antibody, titre | -0.067 (-0.248, 0.114) | 0.47 | -0.010 (-0.176, 0.157) | 0.90 |
a P < 0.05 |
Abbreviations; anti-CCP antibody, anti-cyclic citrullinated peptide antibody; CI, confidence interval; DAS28-ESR, disease activity score 28-erhytrocyte sedimentation rate; FVC, forced vital capacity; ILD, interstitial lung disease. |