Neuropathic pain: Outcome measures and their psychometric properties
Neuropathic pain (NeP) is one of the most common chronic pain conditions, causing activity limitations and participatory restrictions among adult population. Diabetes is considered to be the most common cause of NeP in both developed and developing countries. Diabetes induced NeP not only produces severe pain, tingling and numbness sensation in the involved limbs (typical Glove and Stocking appearance), but also limits physical function due to loss of sensation. There are no recommended methods for clinical situation to measure these signs and symptoms. However, in research situations such as NeP clinical trials, studies have been using both generic and disease-specific patient-reported outcome measures (PROMs) to assess and evaluate changes in pain and physical functioning status following an intervention. In order to capture a real change in the variables of interest, the psychometric properties of a particular measure should be within acceptable limits. Various outcome measures (OMs) have been used in the literature for NeP, with different dimensions of psychometric properties (reliability/validity/responsiveness). However, there is no definitive synthesis of evidence of the psychometric properties of these measures. Therefore, the aim of this thesis was to investigate the psychometric properties of the available measures, and recommend a core set of OMs for the assessment of pain and physical function in diabetic peripheral neuropathic pain (DPN) conditions.This thesis involved a multiple step approach to fulfil its objectives. Initially, a systematic review of systematic reviews was undertaken to explore the range of OMs available in the literature according to the classification of Initiative on Methods, Measurement and Pain Assessment in Clinical Trials guidelines. The methodological quality of the included reviews was evaluated on the Preferred Reporting Items for Systematic reviews and Meta-Analyse checklist. The study suggested that there is a lack of consensus for the most commonly used measures for assessing these domains. The first recommended OM domain, that is, ‘Pain’ was the most commonly used identified OM (n= 40/48). Despite evidence that pain may impact upon function, ‘Physical functioning’ was not a usual OM in NeP clinical trials (n= 11/48). As the next step, another systematic review was conducted to assess the psychometric properties (reliability/validity/responsiveness) of the identified pain and physical function measures in general NeP conditions. The methodological quality of the included studies was evaluated on the COnsensus based Standards for the selection of health status Measurement INstruments guidelines. The findings of this study revealed that the most commonly used pain and physical function measures were either not assessed for all the available psychometric properties, or were graded poor for their methodological quality for the established properties. The studies with high methodological quality used two measures for pain and physical function domains in a NeP population (modified Brief Pain Inventory for Diabetic Peripheral Neuropathic pain scale: mBPI-DPN) and physical function (short form Screening of Activity Limitations and Safety Awareness scale: sSALSA). As these two measures were not assessed for all of the psychometric properties, further evaluation (for the properties which were not evaluated so far) of these two identified measures was required before any final recommendation could be made. The next phase of the thesis involved a cohort study, focused on evaluating the reliability, validity, and on the responsiveness of the identified measures: pain (mBPI-DPN scale) and physical function (sSALSA scale), in a DPN population. Data from 38 participants was collected at baseline, four weeks, and twelve weeks assessment at the Centre for Health Activity and Rehabilitation Research, School of Physiotherapy, University of Otago, Dunedin, New Zealand. Multiple recruitment strategies were adopted to recruit participants from wider geographical locations (fifteen different locations throughout the New Zealand). Test-retest reliability (that is, relative form and absolute form) was calculated between two sessions conducted four weeks from the baseline assessment. Convergent validity was assessed between the mBPI-DPN pain interference scale and the sSALSA scale. Responsiveness, Minimal Clinically Important Difference (MCID) scores for the mBPI-DPN and the sSALSA scale were calculated using two approaches: an anchor based and a distribution based approach. Both outcome measures demonstrated acceptable test-retest reliability (mBPI-DPN scale: ICC= 0.61, SEM= 12.92; and the sSALSA scale: ICC= 0.81, SEM= 4.88) and convergent validity (between the mBPI-DPN pain interference scale and the sSALSA scale, Spearman’s correlation coefficient r= 0.62). The computational methods used in different methodologies to calculate MCID scores for the mBPI-DPN and the sSALSA scale were varied, hence the magnitude of derived MCID scores also varied. This situation clearly raises the issue of the practical utility of such scores in clinical and research applications. The findings from this thesis contribute to the current knowledge of the available OMs, and psychometric properties of these measures in NeP clinical trials. The findings of the cohort study provide the basis for future research in this area.
Advisor: Baxter, G. David; Claydon, Leica S.; Mani, Ramakrishnan
Degree Name: Doctor of Philosophy
Degree Discipline: School of Physiotherapy
Publisher: University of Otago
Keywords: Neuropathic pain; outcome measures; psychometric properties; diabetic neuropathic pain; reliability; validity; responsiveness
Research Type: Thesis