Transcutaneous electrical nerve stimulation (TENS) for patients with upper limb complex regional pain syndrome: a feasibility study

1. Pain
Pain will be measured using a simple pain Visual Analogue Scale (VAS) with patients asked to rate the pain in their affected limb using the following statement 'How would you rate your average pain over the last two days' with anchor statements of 'no pain' and 'worst imaginable pain'. The VAS will be collected at baseline, post treatment and at the 3-month follow-up. Patients will also be asked to keep a pain diary where they rate their pain on a numerical rating scale (0-10) four times (morning, afternoon, evening and night) each day using the following statement 'How would you rate your pain at this point in time' with anchor statements of 'no pain' and 'worst imaginable pain'.

2. Pain Medication Use
Participants will monitor their daily medication use in a diary over the course of the study. Participants will be asked to record for each day if pain medication for the CRPS pain was used, and if so what type of medication and what dosage (number of pills and size [mg] of pills).

3. Function
Function will be assessed using the Disabilities of the Arm, Shoulder and Hand test (DASH), a 30-item questionnaire that is scaled from 0-100. It asks the patient about their ability to perform various daily tasks on a 0-5 Likert scale, which is then transposed onto a 0-100 scale

4. Hand Laterality Recognition Task
Correctly identifying the laterality (i.e. 'left' or 'right') of an image depicting a hand requires the participant to engage in the mental rotation (motor imagery) of their own limbs, with optimal performance relying on an intact body schema. Participants will be assessed using a version of this 'Hand Laterality Recognition Task' (HLRT). They will be presented with images of hands on a computer screen that vary in their laterality, view, orientation and rotation; and asked to respond as quickly and as accurately as possible (by pressing one of two keys on a computer keyboard). Presentation of stimuli (images) and resulting data (accuracy and response time) will be controlled and logged using customized software (E-Prime, www.pstnet.com).

5. Bath CRPS Body Perception Disturbances (BPD)
The BPD is a questionnaire which assesses a patients' perception of their affected limb. Participants rate different aspects of perception such as feelings of ownership and attention. Five of the items are on a 0-10 scale, two of the items are yes/no answers and the final item is graded on a 0-1-2 scale. A total score is scaled from 0-57. Higher scores denote poorer perception of the limb.

The primary outcomes will be measured at baseline, three weeks and three months.

1. Placebo/blinding credibility
To investigate the appropriateness of the single-blinding procedures the participants will be asked to make a judgement (at the 3-month follow-up by the treating clinician RK) as to which group they were randomised to. The blinding assessment method will ask the participants two questions. The first question 'do you believe your TENS unit was functioning properly?' has five possible responses:
1. I am certain my TENS unit was working properly
2. I think my TENS unit was probably working properly
3. I have absolutely no idea whether the TENS unit was working properly or not
4. I think my TENS unit was probably not working properly
5. I am certain my TENS unit was not working properly
The second question will ask 'If above you answered '3) I have absolutely no idea whether the TENS unit was working properly or not' what would you guess':
1. Functioning properly
2. Not functioning properly
This assessment method has been previously used previously by MJ and others in the TENS field.

2. Adverse reactions
If any participant reports an adverse reaction this will be recorded on an adverse reaction recording form designed by the Teesside University research and ethics board, which records severity, relationship to the intervention, action taken and outcome at date ceased.

3. Recruitment/eligibility
The number of participants recruited into the study over the 20-month period will be used to judge the recruitment rate. Additionally the number of participants invited to take part but not meeting the eligibility criteria on formal screening will be recorded to assess the eligibility criteria.

4. Qualitiative interviews
All participants will undertake an exit interview at the three-month point. At this point patients' perceptions of the intervention in relation to objectives 1 and 2 will be asked. A semi-structured interview approach will be used. The interviews (<20 minutes) will be audio-recorded and transcripts typed out verbatim. The interviews will be analysed using thematic analysis. The interview topic guide for the questions will be as follows:
1. What were your general impressions of the treatment?
2. What were your expectations of treatment and to what degree do you feel these expectations were met?
3. What is your opinion of the usability and acceptability of the intervention/placebo?
4. What is your opinion about using this intervention in the future?
5. Is there anything else you would like to say about the intervention/study?
The following prompt questions will be used at appropriate times within the interview: why? why not?, can you give me an example? At the beginning and end of the study participants will be asked to rate the following:
A. How helpful do you believe TENS will be for your pain on a 0-10 scale: 0 = not at all helpful 10 = extremely helpful
B. How helpful do you believe sub-threshold TENS will be for your pain on a 0-10 scale: 0 = not at all helpful 10 = extremely helpful
C. How easy to use do you think TENS will be: 0 = not at all easy to use 10 = extremely easy to use.

The secondary outcomes will be measured at baseline, three weeks and three months.