Modified Medical Research Council Dyspnea Scale in GOLD Classification Better Reflects Physical Activities of Daily Living

BACKGROUND: In multidimensional Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification, the choice of the symptom assessment instrument (modified Medical Research Council dyspnea scale [mMRC] or COPD assessment test [CAT]) can lead to a different distribution of patients in each quadrant. Considering that physical activities of daily living (PADL) is an important functional outcome in COPD, the objective of this study was to determine which symptom assessment instrument is more strongly associated with and differentiates better the PADL of patients with COPD.

METHODS: The study included 115 subjects with COPD (GOLD 2–4), who were submitted to spirometry, the mMRC, the CAT, and monitoring of PADL (triaxial accelerometer). Subjects were divided into 2 groups using the cutoffs proposed by the multidimensional GOLD classification: mMRC <2and ≥2 and CAT <10 and ≥10.

RESULTS: Both mMRC and CAT reflected the PADL of COPD subjects. Subjects with mMRC <2 and CAT <10 spent less time in physical activities <1.5 metabolic equivalents of task (METs) (mean of the difference [95% CI] = −62.9 [−94.4 to −31.4], P < .001 vs −71.0 [−116 to −25.9], P = .002) and had a higher number of steps (3,076 [1,999–4,153], P < .001 vs 2,688 [1,042–4,333], P = .002) than subjects with mMRC >2 and CAT >10, respectively. Physical activities ≥3 METs differed only between mMRC <2 and mMRC ≥2 (39.2 [18.8–59.6], P < .001). Furthermore, only the mMRC was able to predict the PADL alone (time active, r² = 0.16; time sedentary, r² = 0.12; time ≥ 3 METs, r² = 0.12) and associated with lung function (number of steps, r² = 0.35; walking time, r² = 0.37; time <1.5 METs, r² = 0.25).

CONCLUSIONS: The mMRC should be adopted as the classification criterion for symptom assessment in the GOLD ABCD system when focusing on PADL.