Increased Red Blood Cell Distribution Width in the First Year after Diagnosis Predicts Worsening of Systemic Sclerosis-Associated Interstitial Lung Disease at 5 Years: A Pilot Study

The course of systemic sclerosis-associated interstitial lung disease (SSc-ILD) varies among individuals. Red blood cell distribution width (RDW) has been reported to be a predictor of idiopathic pulmonary fibrosis. However, there are no studies on the relationship between RDW and SSc-ILD. We conducted a retrospective study of 28 patients who were diagnosed with SSc-ILD on their first visit to our hospital and were followed-up for 5 years. The correlation between the changes in RDW, KL-6, and SP-D (Delta RDW, Delta KL-6, Delta SP-D) and the changes in percent-predicted forced lung volume and % carbon monoxide diffusion (Delta%FVC, Delta%DLco) was investigated. Delta RDW at 1 year after diagnosis was significantly inversely correlated with Delta%FVC at 5 years after diagnosis (r = -0.51, p < 0.001) and Delta%DLco at 5 years after diagnosis (r = -0.47, p < 0.001), whereas Delta KL-6 and Delta SP-D at 1 year were not correlated with Delta%FVC or Delta%DLco at 5 years. In the group of SSc-ILD patients with RDW increase in the first year after diagnosis, %FVC and %DLco were significantly lower than baseline at 3-, 4-, and 5-year assessments. In the group of patients without RDW increase in the first year, %FVC and %DLco did not decrease during the follow-up period. In conclusion, the changes in RDW in the first year after diagnosis may be useful surrogate markers to predict the long-term course of SSc-ILD.