Clinical background
The mMRC (Modified Medical Research Council) dyspnoea scale serves a specific purpose in the management of COPD: to quantify how far breathlessness limits the patient's physical activity, independently of spirometric grade. The need arose because FEV₁ correlates only weakly with symptom burden and functional impairment in COPD [1]. Two patients with the same FEV₁ per cent predicted may have entirely different capacity in daily life, and treatment decisions, particularly the choice of pharmacological escalation and referral to pulmonary rehabilitation, are guided largely by symptoms and not by lung function alone.
In the GOLD ABE classification, mMRC is used as one of two options for assessing symptoms, with the threshold mMRC ≥ 2 defining a significant symptom burden and placing the patient in group B or E (previously B and D respectively) [3]. This is the main decision the instrument directly influences in modern COPD practice.
Applying the mMRC scale
The mMRC is an ordinal scale with five grades (0 to 4) in which the patient, or the clinician, selects the description that best matches the patient's breathlessness in relation to physical activity:
| Grade | Description |
|---|---|
| 0 | Breathless only with strenuous exercise |
| 1 | Breathless when hurrying on level ground or walking up a slight hill |
| 2 | Walks slower than people of the same age on level ground because of breathlessness, or has to stop for breath when walking at own pace |
| 3 | Has to stop for breath after walking about 100 metres or after a few minutes on level ground |
| 4 | Too breathless to leave the house, or breathless when dressing or undressing |
The instrument is not a formula but a categorical assessment. No points are summed; a single grade is chosen on the basis of the description that best matches the patient's exertional breathlessness.
The original MRC scale used grades 1 to 5. The modified version (mMRC) shifted to 0 to 4 but kept the descriptions unchanged. Validation of the MRC scale as a measure of function in COPD was carried out by Bestall et al. in a cohort of 100 patients with COPD recruited from an outpatient pulmonary rehabilitation programme in London [1]. The study included only patients with MRC grade 3 to 5 (corresponding to mMRC 2 to 4), which means that the lower grades were not validated in the derivation cohort. Patients were assessed with spirometry, blood gases, the shuttle walking test, the Borg scale, SGRQ, CRQ, the Nottingham Extended Activities of Daily Living scale and HAD. The MRC grade correlated significantly with walking distance (shuttle distance), quality-of-life measures (SGRQ and CRQ), activity level (EADL) and mood, but not with FEV₁ [1]. The conclusion was that the scale is a valid complement to spirometry for categorising functional impairment in COPD.
Interpretation in practice
The mMRC is used clinically in two main ways: as a threshold for treatment decisions and as a follow-up measure.
| mMRC grade | Clinical significance | Concrete action |
|---|---|---|
| 0 to 1 | Low symptom burden | Routine follow-up; no escalation of symptomatic treatment on the basis of breathlessness alone |
| ≥ 2 | Significant symptom burden | By GOLD ABE the patient is placed in symptom group B or E; consider escalation to LAMA/LABA, assess the need for pulmonary rehabilitation and review the level of physical activity |
| 3 to 4 | Severe functional impairment | Strongly indicated for pulmonary rehabilitation; assess the need for oxygen therapy, a palliative perspective and social support |
The threshold of mMRC ≥ 2 is the single most important clinical cut-point and is used in the GOLD guidelines to separate patients with more symptoms from those with fewer [3]. A patient who reaches grade 2 or higher should therefore not be followed with spirometry alone but actively offered interventions aimed at relieving symptoms and preserving function.
At follow-up after an intervention, for example pulmonary rehabilitation, a change of one grade can be regarded as clinically meaningful, but the scale has limited sensitivity to change and should be supplemented with more responsive instruments if measuring change is the main purpose [3].
Validation and performance
Bestall et al. found in the derivation cohort that the MRC grade discriminated well between patients in terms of walking distance and quality of life, but the cohort was small (n = 100) and included only patients with moderate to severe breathlessness (grade 3 to 5) [1].
In the COPDGene cohort (4,484 patients with COPD, smokers with ≥ 10 pack-years), Han et al. compared mMRC with the SGRQ as the symptom instrument for GOLD classification [3]. Agreement between the two instruments was good but not perfect (kappa = 0.77). The choice of symptom instrument affected category assignment: with mMRC, 34% were classified as group A and 38% as group D, whereas the corresponding figures with the SGRQ were 29% and 41%. The greatest discrepancy was seen in group C, where only 47% of patients classified as C with mMRC received the same classification with the SGRQ. The authors also noted that the SGRQ and the CAT are more repeatable and more sensitive to change than mMRC [3].
Jones et al. analysed 1,817 COPD patients in primary care and found that mMRC ≥ 2 classified 57% of patients as having few symptoms (GOLD group A or C), compared with 17% when CAT ≥ 10 was used as the threshold [2]. mMRC ≥ 1, by contrast, gave a classification close to that of CAT ≥ 10. Even patients with mMRC grade 0 had moderately raised SGRQ and CAT scores, indicating that mMRC underestimates symptom burden compared with multidimensional instruments [2].
A qualitative validation study by Sunjaya et al. used cognitive interviews with 16 participants and found considerable heterogeneity in how patients ranked the mMRC descriptions, particularly for grades 0, 2 and 3 [4]. Grades 2 and 3 did not appear to function as clear discriminators, which raises questions about the scale's ability to separate adjacent levels of function.
In the COCOMICS study (3,633 Spanish COPD patients), Almagro et al. compared mMRC and FEV₁ as prognostic markers of 5-year survival [5]. New FEV₁ thresholds predicted mortality significantly better than mMRC, than FEV₁ by GOLD, and than the BODE index cut-offs. mMRC therefore had limited value as a stand-alone prognostic instrument.
Limitations
The mMRC measures only breathlessness in relation to physical activity and does not capture other important COPD symptoms such as cough, sputum, fatigue or the psychosocial consequences of the disease. This is a systematic weakness compared with the CAT, which is multidimensional [3]. A patient with severe cough and sputum production but without marked exertional breathlessness may score a low mMRC despite a considerable symptom burden.
The scale is subjective and rests on the patient's own understanding of what constitutes "hurrying" or "the pace of people of the same age", which makes it sensitive to individual interpretation. The qualitative study by Sunjaya et al. showed that grades 2 and 3 in particular can be difficult for patients to distinguish [4].
The mMRC has limited sensitivity to change over time. For following treatment effect, for example after pulmonary rehabilitation, supplementation with the CAT or specific walking tests such as the six-minute walk test is recommended [3].
The derivation cohort included only patients with mMRC 2 to 4, which means that the scale's ability to discriminate between grades 0 and 1 was not directly validated in the original study [1]. The instrument was furthermore developed and validated for COPD and should not be transferred uncritically to other conditions causing breathlessness, such as heart failure or interstitial lung disease, without specific validation in those populations.
References
- Bestall JC, Paul EA, Garrod R, et al. Usefulness of the Medical Research Council (MRC) dyspnoea scale as a measure of disability in patients with chronic obstructive pulmonary disease. Thorax 1999. PMID: 10377201
- Jones PW, Adamek L, Nadeau G, et al. Comparisons of health status scores with MRC grades in COPD: implications for the GOLD 2011 classification. Eur Respir J 2013. PMID: 23258783
- Han MK, Muellerova H, Curran-Everett D, et al. GOLD 2011 disease severity classification in COPDGene: a prospective cohort study. Lancet Respir Med 2013. PMID: 24321803
- Sunjaya A, Poulos L, Reddel H, et al. Qualitative validation of the modified Medical Research Council (mMRC) dyspnoea scale as a patient-reported measure of breathlessness severity. Respir Med 2022. PMID: 36179385
- Almagro P, Martinez-Camblor P, Soriano JB, et al. Finding the best thresholds of FEV1 and dyspnea to predict 5-year survival in COPD patients: the COCOMICS study. PLoS One 2014. PMID: 24587085
