Limitations to the 6-Minute Walk Test in Dermatomyositis with Interstitial Lung Disease in Comparison with Idiopathic Interstitial Pneumonia

Although the relationship between muscle strength and exercise capacity has been demonstrated in dermatomyositis without lung dysfunction, little is known about the association between exercise capacity and interstitial lung disease in dermatomyositis. Eleven patients with dermatomyositis with interstitial lung disease without the manifestation of muscle weakness and 12 patients with idiopathic interstitial pneumonia underwent the 6-minute walk test (6MWT). PaO(2), creatine kinase, percentage predicted 6MWT distance (6MWD%), and SpO(2) at rest were similar between patients. Percentage predicted vital capacity, carbon monoxide diffusing capacity (DL(CO)%), and SpO(2) after 6MWT were higher and exertional dyspnea was lower in patients with dermatomyositis than in patients with idiopathic interstitial pneumonia. SpO(2) after 6MWT was positively correlated with 6MWD% in patients with dermatomyositis, while DL(CO)% and PaO(2) were positively correlated with 6MWD% in patients with idiopathic interstitial pneumonia. Lung dysfunction in dermatomyositis might not be a major limitation factor in exercise capacity.