Investigating the psychometric properties of patient reported outcome measures in individuals with chronic diabetic neuropathic pain: prospective longitudinal cohort study protocol

Abstract

Background:

The prevalence of diabetes in New Zealand is estimated to be 7% of the total population. And higher incidence rates of peripheral neuropathic pain (NeP) in diabetic populations have been estimated (between 3 and 25%). A range of outcome measures (OMs) are used to evaluate a change following an intervention, in diabetic NeP clinical trials, but very few have adequate psychometric properties (PMPs) for key dimensions. This study aims to investigate the remaining PMPs (which have not been investigated so far) of established specific pain intensity and physical functional OMs in adults (⩾18 years) with chronic diabetic NeP.

Methods and analysis:

This prospective longitudinal cohort study aims to recruit a total of 80 adults with diabetic NeP in Dunedin, Otago region, New Zealand, from November 2013. Outcomes include two questionnaires: Pain OM – modified brief pain inventory (mBPI)-diabetic peripheral neuropathy item scale; and physical functional OM – screening of activity limitation and safety awareness (SALSA) scale. To capture the reliability and validity of these measures two follow-up assessments (4 and 12 weeks after the baseline assessment) will be scheduled. For test–retest reliability, ‘Intraclass Correlation Coefficient’ (ICC), and to find out the correlation between two measures, ‘Pearson correlation coefficient’ will be calculated. To investigate responsiveness, ‘Minimally Clinically Important Change' (MCIC) scores will be calculated.

Ethics and Dissemination:

Full final ethical approval from the University of Otago Human Ethics Committee has been obtained: Ethical Committee reference number H13/041. Maori Research Consultation through the Ngāi Tahu Research Committee has also been undertaken. Trial registration: The Australian New Zealand Clinical Trials.

Keywords:

• Diabetic neuropathy
• Pain intensity outcome measure
• Physical functioning outcome measure
• Psychometric properties
• Reliability
• Validity
• Responsiveness

Acknowledgements

The authors thank and acknowledge Prof Chad Cook, for his suggestions, invaluable constant assistance, and helping with constructive feedback on drafts of the manuscript. We would like to express our gratitude to Centre for Health Activity and Rehabilitation Research, School of Physiotherapy, University of Otago, New Zealand departmental funds to partly support this study. We would also like to acknowledge the Mark Steptoe Memorial Trust, School of Physiotherapy, University of Otago, New Zealand, for providing the rest of financial assistance.