Defining the minimal important difference for the visual analogue scale assessing dyspnea in patients with malignant pleural effusions

Our plain-English summary of Defining the minimal important difference for the visual analogue scale assessing dyspnea in patients with malignant pleural effusions, by E.K. Mishra, J.P. Corcoran, R.J. Hallifax, et al (PloS One, 2015).

The study

• Authors: E.K. Mishra, J.P. Corcoran, R.J. Hallifax, J. Stradling, N.A. Maskell, N.M. Rahman
• Journal: PloS One
• Published: 2015;10(4):e0123798
• Cited by: 50 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The minimal important difference (MID) is essential for interpreting the results of randomised controlled trials (RCTs). Despite a number of RCTs in patients with malignant pleural effusions (MPEs) which use the visual analogue scale for dyspnea (VASD) as an outcome measure, the MID has not been established.

Methods: Patients with suspected MPE undergoing a pleural procedure recorded their baseline VASD and their post-procedure VASD (24 hours after the pleural drainage), and in parallel assessed their breathlessness on a 7 point Likert scale.

Findings: The mean decrease in VASD in patients with a MPE reporting a 'small but just worthwhile decrease' in their dyspnea (i.e. equivalent to the MID) was 19mm (95% CI 14-24mm). The mean drainage volume required to produce a change in VASD of 19mm was 760ml.

Interpretation: The mean MID for the VASD in patients with a MPE undergoing a pleural procedure is 19mm (95% CI 14-24mm). Thus choosing an improvement of 19mm in the VASD would be justifiable in the design and analysis of future MPE studies.

In plain English

This study analysed routine clinical questionnaires from breathless adults with confirmed or suspected malignant pleural effusion (cancer-related fluid around the lung) who were having a pleural procedure. Asbestos exposure was not studied, but 24 patients had mesothelioma. Patients marked their breathlessness on a 100mm line before and about 24 hours after the procedure, then rated the change on a 7-point scale. Of 114 questionnaires returned during 2012, 106 had data for the main analysis. Among patients with a malignant effusion who reported a 'small but just worthwhile improvement', breathlessness scores fell by a mean of 19mm (95% CI 14 to 24mm). Before the procedure, patients judged on average that a 24mm improvement (95% CI 21 to 27mm) would be worthwhile, though the authors noted patients found this question hard to grasp. An effect-size method gave just 7.7mm. Overall, 70 of 83 patients (84%) reported a worthwhile or greater benefit. The authors concluded that the smallest worthwhile change for these patients is 19mm. They noted it applies specifically to this group and few patients reported no change or worsening.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Analysis of questionnaire data collected in routine clinical practice (treated as an audit of practice). Patients rated breathlessness before and about 24 hours after a pleural procedure, with a 7-point Likert scale used as an anchor.
• Who was studied: Breathless adults with confirmed or suspected malignant pleural effusion undergoing a pleural procedure, in the authors' clinical practice (authors based at the Oxford Centre for Respiratory Medicine, UK). 114/123 questionnaires were returned between January and December 2012, and 106 had data for the primary outcome. Mean age was 70 years and 60 (56%) were female. 92 (81%) had a final diagnosis of malignant pleural effusion. Diagnoses included breast cancer (38), mesothelioma (24) and non-small cell lung cancer (17), and 16 patients had benign effusions.
• Exposure: Not an asbestos exposure study. The intervention was a pleural procedure: diagnostic or therapeutic aspiration, chest drain insertion, indwelling pleural catheter insertion and/or drainage, or local anaesthetic thoracoscopy. Breathlessness was measured on a 100mm visual analogue scale, and the volume of fluid drained in 24 hours was recorded.
• Main results:
  • In patients with a final diagnosis of malignant pleural effusion who reported a 'small but just worthwhile improvement' (20 patients in Table 3), the mean decrease in breathlessness score was 19mm (SD 11mm, 95% CI 14–24mm).
  • When patients with benign effusions were included, the equivalent value was 21mm (95% CI 15–26mm).
  • The improvement patients said in advance would be worthwhile was on average 24mm (95% CI 21 to 27mm). The authors noted that patients found this concept difficult to grasp.
  • Baseline breathlessness score and volume of fluid drained were significant predictors of improvement. Based on this, the mean volume of fluid needed to produce a 19mm improvement was 760ml.
  • Overall, 70/83 (84%) of patients had a worthwhile or greater benefit.
  • Mean improvement differed significantly between the five procedure types (chest drain 41mm, indwelling catheter 41mm, therapeutic aspiration 31mm, diagnostic aspiration 19mm, thoracoscopy 24mm; p = 0.04).
  • After correcting for mathematical coupling using Oldham's method, there was no true correlation between baseline breathlessness and the size of the improvement (r = 0.13, p = 0.21).
  • A statistical (effect-size) method estimated the minimal important difference at only 7.7mm.
• The authors' conclusion: The authors concluded that the minimal important difference for the breathlessness visual analogue scale in patients with malignant pleural effusions undergoing a pleural procedure is 19mm (95% CI 14 to 24mm). They judged statistical estimation methods unreliable in this context, and patient-opinion methods a possibly reasonable substitute for anchor methods.
• Limitations the authors state:
  • The estimate applies specifically to patients with malignant pleural effusion undergoing a pleural procedure.
  • Very few patients reported a not-worthwhile improvement, no change or deterioration, making it difficult to separate the minimal important difference from these categories.
  • Numbers for some procedures were small, so the procedure comparisons should be interpreted with caution.
  • The correlation between drainage volume and improvement was weak, so the authors said the 760ml figure should not guide treatment of individual patients.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma, Ovarian cancer.

Medical terms in this study, explained in our Lexicon: Dyspnea, Pleural Effusion.

Related studies

• Aggressive versus symptom-guided drainage of malignant pleural effusion via indwelling pleural catheters (AMPLE-2): an open-label randomised trial — S. Muruganandan, M. Azzopardi, et al. (2018)
• Prognosis of Cancer with Synchronous or Metachronous Malignant Pleural Effusion — J.M. Porcel, C. Solé, et al. (2017)
• Protocol of the Australasian Malignant Pleural Effusion-2 (AMPLE-2) trial: a multicentre randomised study of aggressive versus symptom-guided drainage via indwelling pleural catheters — M. Azzopardi, R. Thomas, et al. (2016)
• Clinically important associations of pleurodesis success in malignant pleural effusion: Analysis of the TIME1 data set — R.M. Mercer, J. Macready, et al. (2020)
• Satisfactory results of a psychometric analysis and calculation of minimal clinically important differences of the World Health Organization quality of life-BREF questionnaire in an observational cohort study with lung cancer and mesothelioma patients — M. de Mol, S. Visser, et al. (2018)
• A 70-year-old woman with dyspnea and chest pain — A. Ganesh, M. Flores, et al. (2014)

Browse more research in PloS One, or return to medical research.