Evaluation of individual activity descriptors of the MRC dyspnoea scale: Do they add up?

Introduction: The MRC dyspnoea scale consists of 5 grades that contain of a description of more than one activity. The comparability of these components is not known. We examined the performance of single descriptors of each MRC grade. Methods: Phase I: cognitive debriefing with COPD patients to elicit their understanding of each activity (10 items) of the 5 MRC grades. Phase II: COPD patients completed the MRC scale (grades 1-4) and a MRC-Exploded (MRC-Ex) consisting of 10-items, each representing one activity as described in the MRC grades. Each item used a 4-point response scale (0 9not at all9 to 4 9all of the time9). Rasch analysis was used to assess the pattern of MRC-Ex item severity (logit) to assess the appropriateness of combining individual activity descriptors into single MRC grades. Results: Cognitive debriefing (n=36) identified: MRC 1: meaning of 9strenuous exercise9 unclear and MRC 5: 9too breathless to leave the house9 viewed as "much worse than being breathless with dressing". 203 patients completed Phase II (mean age 64.7years, GOLD: 1:14% 2:41% 3:25% 4:7%). MRC components 3, 4 and 5 are not of equivalent severity, with grade 5 components at least 2 logits apart Conclusions: The MRC has poor reliability due to ambiguity in the degree of severity of the items in Grades 1 and 5. We recommend that 9strenuous exercise9 is removed from MRC grading and that Grade 5 forms separate grades, in particular.