Acute exacerbation of rheumatoid arthritis-associated interstitial lung disease: mortality and its prediction model

Table 2 Cox proportional hazards regression analysis of all-cause mortality

Variables	Univariate model			Multivariate model
Variables	HR	95% CI	P-value	HR	95% CI	P-value
Age, per 1 year increase^a	1.02	0.99–1.06	0.2330	1.02	0.97–1.06	0.4675
Sex, male (vs. female)	0.66	0.36–1.22	0.1845	0.41	0.16–1.05	0.0622
Smoking, ever (vs. never)^a	0.63	0.34–1.20	0.1539
Baseline %FVC, per 1% increase^b	0.97	0.95–0.99	0.0202	0.97	0.95–0.99	0.0168
Baseline %DL_CO, per 1% increase^{b, c}	0.99	0.97–1.01	0.3608
P/F at AE, per 10 Torr increase^a	0.96	0.92–0.99	0.0407	0.94	0.88–0.99	0.0240
C-reactive protein, per 1 mg/dL^a	1.03	0.99–1.06	0.0912
Rheumatoid factor, per 10 U/mL increase^a	1.00	0.99–1.01	0.6296
ACPA, positive (vs. negative)^{b, d}	1.11	0.40–4.65	0.8572
KL-6, per 100 U/mL increase^a	0.97	0.93–1.002	0.0720
UIP pattern on HRCT (vs. other patterns)^b	1.45	0.79–2.76	0.2309
Infection-triggered AE^e	1.98	0.58–5.14	0.2453
Treatment for RA before AE, yes (vs. no)
Prednisolone ≤ 7.5 mg/day	3.33	0.75–14.8	0.1086
Methotrexate	0.73	0.37–1.37	0.3366
Tacrolimus	1.24	0.47–2.75	0.6340
Bucillamine	2.08	0.84–4.45	0.1078
Salazosulfapyridine	1.32	0.63–2.55	0.4416
Treatment for AE (vs. CS monotherapy)
CS + IS	1.05	0.57–1.92	0.8826
CS + IVCY	1.36	0.68–2.70	0.3758
CS + CNI	0.62	0.26–1.35	0.2349

%FVC percent predicted forced vital capacity, %DL_CO percent predicted diffusing capacity of the lung for carbon monoxide, P/F PaO₂/FiO₂ ratio, ACPA anti-cyclic citrullinated peptide antibody, KL-6 Krebs von den Lungen-6, UIP usual interstitial pneumonia, HRCT high-resolution computed tomography, RA rheumatoid arthritis, AE acute exacerbation, CS corticosteroids, IS immunosuppressant, IVCY intravenous cyclophosphamide, CNI calcineurin inhibitor, HR hazard ratio, CI confidence interval
^aAt AE onset
^bWithin 12 months before AE
^cn = 34
^dn = 46
^eDue to an apparent infection with an identifiable cause that occurred within 1 month before AE onset

ISSN: 1465-993X