The effects of transcutaneous electrical nerve stimulation (TENS) on pain and disabilities in the treatment of patients with chronic pain

Proportion of patients satisfied with treatment result and willing to continue treatment. From patients who ceased treatment because they were no longer satisfied with treatment result, the date of cessation of treatment is used for survival analysis.

1. Overall improvement: a percentage change from baseline; nil percent meaning no improvement at all and hundred percent meaning complete recovery.
2. Pain intensity is measured with a 10-centimeter long Visual Analogue Scale (VAS). Descriptors at the beginning and at the end of the scale are 'no pain at all' and 'maximal imaginable pain'. Patients rate their pain at the same time every day for one week.
3. Perceived health status is measured by the sickness impact profile (SIP). The SIP was developed to provide a measure of perceived health status that is sensitive enough to detect changes or differences in heath status that occur over time or between groups. The SIP contains 136 statements about health-related dysfunction in twelve areas of activity (sleep and rest, eating, work, home management, recreation and pastimes, ambulation, mobility, body care and movement, social interaction, alertness behavior, emotional behavior and communication.
4. Disability because of pain is measured with the Dutch version of the Pain Disability Index (PDI). The PDI was developed as a brief, self-report indicator of pain-related disability. It was constructed as a 7-item questionnaire, which is scored on a scale of 0 (no disability) to 10 (total disability). The items ask for the level of limitations in the total range of role functioning: family/home responsibilities, recreation, social activities, occupation, sexual behavior, self-care and life-supporting activities.
5. Duration of TENS use (hours) serves as a measure for compliance. Duration of actual use of the device, is registered during each visit; it can be read out by pressing a special key combination.
6. Placebo credibility is assessed after the initial treatment period (short-term effect) by asking the patients how certain they feel about having a TENS or placebo device, using a questionnaire according to Deyo et al.
7. Co-intervention: Registration of pain medication: The used daily dose/ the defined daily dose ratio is used to calculate the drug load in treatment groups, as published by the World Health Organization (http://www.whocc.no/atcddd/).
8. Adverse effects: Patients are asked to report problems with device or electrodes and are instructed to recognize symptoms of allergy of electrode materials.

Data collection is performed from patients, as long as they are satisfied with treatment result, for a maximum period of one year. At three, six and 12 months after the initial treatment period patients, still satisfied with treatment result, are invited to the outpatient clinic for assessing pain disability, perceived health status and for retrieving data from previous TENS use. Every month, pain diaries are sent by mail to register pain intensity and pain medication use during one week.