Monday 21 March 2011

Blog 2: Investigating the use of various modalities of electrical stimulation for chronic pain – how effective are they?

The general consensus appearing in the literature since the late 1960s, gives credence to the efficacy of various modalities of electrical stimulation (in particular TENS) for the treatment of both acute and chronic pain.  If you happen to be one of many sceptics who question the use of electrotherapy agents in general, we urge you to keep an open mind as we investigate the use of these agents as treatment modalities for chronic pain.


TENS - Transcutaneous electrical nerve stimulation

TENS has been used in the treatment of patients suffering fibromyalgia with modest treatment results even though it has been reported that widespread and poorly localised pain states are less likely to be reactive to TENS (Nijs, 2011). Originally described by Melzack et al (1988), the ‘gate control theory’ remains the preferred explanation for the mechanism of TENS. This theory states that TENS opens large-afferent nerve fibres, which transmit non-nociceptive signals, thereby decreasing transmission through the small afferent fibres that transmit pain. This effect was shown by Itoh (2009) to be persistant for a varied amount of time on cessation of therapy depending on the type of TENS applied.  Cheing & Hui-Chan (1999) reported that a placebo effect may account for up to 32% of treatment success in the use of TENS; however this treatment modality still proved more effective than massage and electroacupuncture for relieving chronic musculoskeletal pain. This was particularly true for high frequency TENS, which was shown to release endogenous opioids from the lumbar cerebrospinal fluid. Durmis (2010) found TENS resulted in an increase in muscle strength, decrease in joint stiffness and decrease in muscle spasm, all of which can contribute to an analgesic effect.

The two most common application modes of TENS include:

1. High frequency/conventional TENS = 40-150Hz, 50-100μs pulse width, low intensity
2. Low frequency/acupuncture-like TENS = 1-4Hz, 100-400μs pulse width, high intensity

Conventional TENS has been associated with a faster onset and shorter duration of analgesia compared to acupuncture-like TENS (Khadilkar, 2005).

3 other standard modes of TENS (Khadilkar, 2005):
1. Brief-intense = >80Hz, >150μs pulse width, comfortable-tolerable intensity
2. Burst mode = bursts <10Hz and comfortable intensity
3. Modulation = one or more stimulation parameters are randomly modulated


PENS - Percutaneous electrical nerve stimulation

PENS combines the advantages of TENS and electroacupuncture in which acupuncture needles are placed in non-acupuncture points. This reportedly leads to pain reduction of up to two hours as endogenous opiods, including  β-endorphin, are released due to the stimulation (Yokoyama, 2004).  Yokoyama (2004) does explain that this may have a ceiling effect in which the accumulation of anti-opioid substances within the CNS may account for the development of pain tolerance.  Numerous sources within the literature report that PENS is most effective when delivered at mixed frequencies as this modulation affects the pattern of neurotransmitter release within the CNS and reduces the accommodation effect (Ghoname, 1999 & Yokoyama, 2004):
  • 2Hz - stimulate µ and δ opioid receptors
  • 100Hz - activation k-opioid receptors in CNS
  • Recommended duration = 30 minutes 
Figure 2.0: patient receives PENS acupuncture at Womack Army Medical Centre to address chronic pain he suffers after being wounded in improvised explosive device attacks in Iraq (http://paraglideonline.net/062509_life1.html)

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CCEF - Capacitively coupled electrical field stimulation

CCEF has been reported to potentially increase bone formation by up-regulating osteoblast function (Rossini, 2010). In the study by Rossini, postmenopausal women with multiple vertebral fractures and chronic pain who received CCEF treatment were found to decrease their intake of NSAIDS, however no other differences were noted in comparison to the control group.  No side effects were reported with this treatment, even with long duration of use.  Once again, it was suggested by the authors who conducted the study that a placebo effect may have come into play in decreased pain perception.


TCES – Percutaneous transcranial electrical stimulation

TCES activates opiate mechanisms in the brain's anti-nociceptive system, resulting in β-endorphin, serotonin and noradrenalin release (Gabis, 2009). Analgesia was found to be concentrated within the raphe (medial brainstem).  Gabis (2010) explained that 40% of patients receiving placebo TCES reported pain relief; this again suggests to us that the placebo effect is very powerful when treating chronic pain.  However, Gabis further reported decreased pain in the placebo group which was maintained at 3 months which suggests a vanishing placebo.

Please click HERE to watch an instructional video on how TCES is applied.


rTMS – Repetitive transcranial magnetic stimulation

rTMS stimulates the cerebral cortex over either the motor cortex or the dorsolateral prefrontal cortex, which produces analgesic effects up to three weeks post-treatment(Nijs, 2011). This safe, non-invasive technique for treating chronic pain is more effective in suppressing central pain as opposed to peripheral pain as it targets cerebral structures involved in pain processing (see Blog 1).  Unfortunately, there is limited equipment availability due to its bulk and expense, which creates a limitation in prescribing this technique as part of a patient’s pain management regime – only a few specialised centres have these available.

Please click HERE to watch a video outlining how rTMS works and how this is helping patients with depression.

Upon review of the various electrical stimulation techniques used in the management of chronic pain, we found that most of the evidence seems to point to a placebo effect coming into play rather than a specific analgesic effect of the modalities discussed. The research seems to aim to demonstrate that electrical stimulation (particularly TENS) is a superior treatment method in comparison to placebo effects.  This is something which we feel warrants further investigation and we will be discussing in our next blog.

3 comments:

  1. This is very high quality work. I wish all your peers could read this posting. I particularly appreciate your use of numerals to track and link your postings. Could you say which group of medical professionals uses the more invasive types of estims for chronic pain - is it physicians or psychiatrists or physical therapists working in a chronic pain team? CY

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  2. Also - the first video link you psoted contained an error and I couldn't watch it. The second one on TMS was fine - and indeed answered my question from the earlier comment. thanks CY

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  3. We have updated the link for the first video and it is now working without any problems.
    emilynat

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