Is Transcutaneous Electrical Nerve Stimulation (TENS), as proveide in daily care, an effective method to modulate pain transmission in patients suffering from chronic non-specific pain syndromes?

Transcutaneous electrical nerve stimulation (TENS) is a frequently applied
therapy in chronic pain. Although evidence regarding the effectiveness of TENS
in chronic pain is inconclusive many patients continue using TENS on long term
in daily practice.
An important question is therefore why some patients respond well and others
don*t at all.
Due to the heterogeneity of chronic pain patients, where psychosocial factors
may influence pain, one cannot expect that all patients will respond equally to
TENS. In chronic pain evidence for abnormal pain processing (sensitization) has
been found in several patients groups. The process of sensitization might
influence effectiveness of TENS as the theoretical working mechanism of TENS is
based on the modulation of the transmission of nociceptive impulses form
peripheral receptors throughout spinal nerve system into the brain. The
question is whether the effect in the responder group is due to an adequate
modulation of pain transmission or do other factors influence the ability to
modulate this process?
In this study we want to study the effect of TENS on pain transmission, as
measured by contact heat evoked potentials (CHEPS), between *responders* and
non-responders* after a two weeks TENS treatment. A subjective pain reduction
of >= 30% on a 100 mm Visual Analogue Scale (VAS) is regarded as a clinical
relevant score. Therefore *responders* will be defined as patients with a pain
reduction of >= 30% on a VAS after a two week treatment period with TENS.
Non-responders are patients with a pain reduction < 15%.

Is effectiveness of TENS, in reducing pain, in responders based on modulation
of pain transmission and perception, as measured by CHEPS? Is the ability of
TENS to modulate pain transmission and perception influenced by abnormal pain
processing? Are sensory and/or pain thresholds at baseline predictive factors
voor effect of TENS, based on responders/ nonrespondersship?

prospective cohort study

Patients receive a two week treatment period with TENS-treatment at home after
instruction. The frequency is set at 100 Hz and pulse duration at 250 µ sec.
Patients have to use the TENS daily (minimal 4 times a day for 30 minutes).

Effectiveness of TENS treatment in chronic pain is still inconclusive. This
study provides information about possible subgroups of patients who will have
better outcome for TENS. Results of this study can help to identify possible
subgroups of patients who will benefit from TENS. Being able to identify
patients with favourable outcome, may allow efficient selection, while reducing
the cost and disappointment of non-success in general practice. Criteria to
select patients at poor or good outcome could also be used in randomised
trials. The risk associated with participation in TENS treatment can be
considered negligible and the burden minimal. TENS treatment is regarded as a
safe and easy to administer intervention.
The measurementsprotocol is without risk en are combined with treatment
appointments. De duration of the measurement is about 2.5 houres (each time),
which is a normal duration as performed in daily clinical practice. Total
duration of maesurements is 5 houres.