Visual analogue scales for interstitial lung disease:a prospective validation study

Rationale: Visual analogue scales (VAS) are simple symptom assessment tools which have not been validated in interstitial lung disease (ILD). Simple measures of ILD disease burden would be valuable for non-specialist clinicians monitoring disease away from ILD specialist centres. Objective: To validate VAS to assess change in dyspnoea, cough and fatigue in ILD, and to define the minimal clinically important difference (MCID) for change in these.METHODS:64 patients with ILD completed VAS for dyspnoea, cough and fatigue. Baseline King's Brief ILD questionnaire (K-BILD) scores, lung function and 6-minute walk test results were collected. Tests were repeated 3-6 months later, in addition to a 7-point Likert scale. The MCID was estimated using median change in VAS in patients who reported "small but just worthwhile change" in symptoms at follow-up. Methods were repeated in a validation cohort of 31 ILD patients to confirm findings. Results: VAS scores were significantly higher for patients who reported a "small but just worthwhile change" in symptoms versus "no change" or "not worthwhile change" (p < 0.01). The MCID for VAS Dyspnoea was estimated as 22.0mm and 14.5mm for VAS Fatigue. These results were reproducible in the validation cohort. Results were not significant for VAS Cough. Change in VAS Dyspnoea correlated with change in K-BILD (r=-0.51, p < 0.01), forced vital capacity (r=-0.32, p = 0.01) and 6-minute walking distance (r=-0.37, p = 0.01). Conclusion: The VAS is valid for assessing change in dyspnoea and fatigue in ILD. The MCID is estimated as 22.0mm for dyspnoea and 14.5mm for fatigue. This could be used to monitor disease in settings away from ILD specialist review