Aerobic exercise capacity in patients with juvenile dermatomyositis

To examine the feasibility of maximum exercise testing in patients with juvenile dermatomyositis (JDM), characterize the maximum oxygen consumption (VO2peak) of these patients, and determine if exercise time could be used as an surrogate index for VO2peak.

Fifteen patients diagnosed with JDM (age 5-14) performed a graded, maximum exercise test using a motor driven treadmill and metabolic cart to volitional exhaustion conforming to the Bruce protocol.

All patients were able to perform the exercise test. Ten of the 15 patients performed a maximal effort (heart rate > 180 beats/min or respiratory exchange ratio > 1.0). The patients who had a maximal exercise performance, the mean absolute VO2peak, relative VO2peak (related to body mass), and exercise time were respectively -1.82 (+/- 1.5), -2.83 (+/- 1.9), and -3.65 (+/- 1.9) standard deviations lower compared to age and sex matched reference values (p < 0.05). Z scores for exercise time were significantly lower compared to Z scores for absolute and relative VO2peak, an indication of reduced muscular economy. When exercise time was converted to VO2peak using the equation: VO2peak = 0.1583 (exercise time) + 0.0828, the VO2peak values were not significantly different from the measured VO2peak values.

Aerobic exercise testing on a treadmill was possible in patients with JDM and revealed an impairment in their maximal aerobic exercise capacity. Exercise time can be used as an indicator of VO2peak, when converted to VO2peak using a regression equation. VO2peak, measured or estimated, has the potential to be a good indicator of muscle function in patients with JDM.