Determining the Minimal Clinically Important Difference for 6-Minute Walk Distance in Fibromyalgia.

The analysis came from a trial of exercise adherence, not a study designed to estimate the MCID, so the thresholds may not apply to other medical or exercise interventions. The sample was mostly middle-aged women with moderate-to-severe physical impairment and pain, so the estimates may not apply to men or patients with less severe fibromyalgia. The correlations between change in walking distance and change in patient-reported outcomes were small, with values of -0.20, -0.25, and 0.20 at week 36, so the link to patient-perceived meaning is weak. The MCID estimates were notably higher than published values in cardiac, heart failure, and lung disease populations, and the authors noted they may be unattainable for many patients with fibromyalgia. 187 of 216 enrolled patients had complete data; the paper says excluded patients did not differ significantly at baseline, but the final sample was smaller than the trial. Participants completed two 6-minute walk trials at each visit, which may have affected performance because fatigue is common in fibromyalgia, although the two trials were highly correlated (r=0.92). The test may have limited ability to detect change in patients with higher exercise capacities because of a ceiling effect.

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Do not use 156 or 167 meters as a firm cutoff to decide whether a fibromyalgia treatment worked. The correlations between change in walking distance and change in patient-reported outcomes were small, and the authors said these thresholds may be unattainable for many patients.