Background/Purpose:

Interstitial lung disease in patients with polymyositis (PM) and dermatomyositis (DM) is characterized by decrease in both lung compliance and pulmonary vascularity, leading to decreased forced vital capacity (FVC) and diffusing capacity for carbon monoxide (DLCO). However, since DLCO is also influenced by the pulmonary circulation, additional pulmonary vascular disease would disproportionally decrease DLCO. This study was aimed to investigate the changes in FVC and DLCO over time in patients with DM and PM and to identify factors associated with disproportional decline in DLCO.

Methods:

A total of 89 DM and 14 PM patients who had been cared at the Rheumatology Clinic of Seoul National University Hospital, a tertiary referral center, from January 2004 to June 2016, with 2 or more pulmonary function tests (PFTs) during follow-up duration, were retrospectively evaluated. FVC and DLCO were expressed as the percentage of values predicted on the basis of patient age, sex, height and weight. Regression was calculated using mixed model with random effect.

Results:

Total of 103 patients with DM and PM were included. The study population was predominantly female (72.8%), with the mean age at diagnosis of 49.9 ± 12.9 years. The mean duration of follow-up was 4.4 ± 3.2 years. There was a strong correlation between FVC and DLCO at baseline (r= 0.618, p<0.001). In 85 (82.5%) of 103 patients, DLCO was lower than FVC by 9.8±14.2% at baseline. There was disproportional change in DLCO relative to FVC over time. Patients with worse decline of DLCO than the change of FVC over time had a higher frequency of Raynaud’s phenomenon (35.1% vs 9.7%, p= 0.021) and positive antinuclear antibody (ANA) (78.4% vs. 48.4%, p=0.012) compared to the patients with better improvement of DLCO relative to FVC over time. There was no significant difference in other clinical and laboratory parameters according to disproportional decline in DLCO relative to FVC. Patients with Raynaud’s phenomenon had significantly higher decline of DLCO from the baseline than those without Raynaud’s phenomenon (-5.6 ± 16 vs 4.4 ± 18.4, p=0.016) and the observed changes of DLCO per year (-9.0 ± 28.3 vs 4.9 ± 29.4 p=0.040).

Conclusion:

In patients with DM and PM, Raynaud’s phenomenon and positive ANA are associated with disproportional decline in DLCO relative FVC. Further prospective studies are needed to determine whether improving pulmonary circulation adds any therapeutic benefit in those idiopathic inflammatory myopathy patients with disproportional decline in DLCO.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/dissociation-of-fvc-and-dlco-in-patients-with-dermatomyositis-and-polymyositis/