Usefulness of six-minute walk test in systemic sclerosis.

The 6-minute walk test (6MWT) is a standardised, feasible and reliable measure of sub-maximal exercise capacity that has never been fully validated in systemic sclerosis (SSc). A variety of data suggest that many non-pulmonary aspects of SSc contribute to the test results, thus blunting the ability of the 6MWT to measure changes in lung function. Sources of variability are a training effect, technician experience, subject encouragement, medication, other activities on day of testing, deconditioning and the effects of musculoskeletal conditions and pain. Another cause of variability is the anatomical site the probe is attached to: a forehead probe is preferable to a finger or earlobe sensor. The indiscriminate use of the 6MWT for all SSc patients is not useful. It should be used in patients with pulmonary involvement, combined with diffusion capacity of the lung for carbon monoxide (DLCO) and its components (membrane diffusion and capillary volume) or the Sclerodermia Health Assessment Questionnaire Disability Index. The use of these combined parameters may indicate the onset of pulmonary hypertension. Recent studies suggest two alternatives to the 6MWT: maximal cardiopulmonary exercise testing and DLCO testing during effort. However, their use must still be validated.