The Correlation Between the Six Minute Walk Test and Spirometric Parameters in Patients with Systemic Lupus Erythematosus

Systemic Lupus Erythematosus (SLE) is an autoimmune disease affect nearly every organ system. Pulmonary involvement, which is a common manifestation of SLE, can remain undiagnosed if asymptomatic. This study aimed to evaluate the efficiency of spirometric findings in early detection of silent pulmonary involvement and examine its correlation with the six minute walk test in SLE patients. In this cross-sectional study fifty patients, who met the American College of Rheumatology criteria for SLE, were recruited from the outpatient rheumatology clinic at the Imam Reza Hospital of Mashhad between July 2013 and September 2014. First, a checklist including demographic information and previous medical documents was completed. Then, spirometry and 6MWT was performed to evaluate subclinical pulmonary involvement and assess patients’ exercise capacity. Based on the results of pulmonary function tests, patients were divided into two groups. A total of 40 patients with normal pattern were placed in one group and 10 patients with restrictive pattern in the other. The difference between SLE patients with and without abnormal spirometry were statistically significant in regard to anti-RNP positivity but total distance walked in six minute, was not significantly different between two groups (p=0.356). Additionally, there were no significant correlations between 6MWD and FVC in SLE patients in the either group as determined by Pearson’s correlation coefficient testing. (R=0.439,P=0.205 in SLE patients with normal spirometry and R=0.191,P=0.237 in those with abnormal pattern) Considering the impact of anti-U1RNP positivity with restrictive pattern on spirometry, it can be deemed as a pulmonary involvement predictor in SLE patients. However, lack of correlation between 6MWT and spirometric parameters is suggestive of restrictive lung involvement, which in turn, demonstrates a multifactorial basis for limited exercise capacity in patients with SLE. Thus, the application of the 6MWT as a measure of pulmonary function is called into question.