Types of TENS:

Currently two types of TENS are being researched for pain and symptom relief treatment of cancer patients. Conventional TENS is the more basic and well-known of the two stimulation types whereas acupuncture-like TENS known as ALTENS aims to produce similar effects despite using different parameters and electrode placements.

TENS Parameters:

The aim of conventional TENS is to selectively stimulate large-diameter A-beta nerve fibres without stimulating other A or C nerve fibres and motor efferents. This means that the electrical impulses generated from the TENS machine are stimulating nerve fibres that are specific to touch and sensation. By stimulating these nerve fibre types, it disrupts the sensation of pain arising in the surrounding tissues and reduces the amount of information regarding the pain being projected to the brain. In theory, high frequency and low intensity pulsed currents would be most effective in achieving this type of stimulation. Large diameter nerve fibres, known as A-beta fibres, have short refractory periods and can generate nerve impulses at high frequencies. The usual frequencies used are 80-120Hz. The intensity (measured in milliamps) of this treatment is highly dependent on the patient, what they can tolerate and what feels good for them. The intensity is therefore adjusted to suit the patient. A standard TENS device delivers biphasic pulsed currents in a repetitive manner using pulse durations of 50–150ms and pulse frequencies of 1–200pulses/s. Effects usually do not last as long as those produced by ALTENS and often do not outlast the duration of the treatment.

Figure 1. A schematic showing TENS affecting the mechanoreceptors of the skin, which then inhibit nocioceptors transmitting signals of pain to the brain, thereby reducing pain perception.
Image retrieved from: Jones, I. & M, Johnson. (2009). Transcutaneous electrical nerve stimulation. Continuing Education in Anaesthesia, Critical Care & Plan, 9(4), 130-135.

ALTENS parameters:

ALTENS is similar to conventional TENS however, the electrodes are placed in areas of the body that would normally represent acupuncture sites. As a result this allows for TENS stimulation as well as acupuncture-like treatments. However, unlike TENS, ALTENS stimulates small diameter A-delta fibres which leads to an opioid release resulting in a decrease in C fibre activity, this effectively decreases pain perception. Another difference between the two types of TENS is the frequency and the intensity that ALTENS offers. ALTENS offers low frequency and high intensity electrical stimulation to the areas applied. In general, ALTENS offers a frequency of 1-10Hz and a pulse duration of 150-300ms. Low frequency/high intensity TENS appears to cause a release of endogenous opioids in the spinal cord and higher brain centres in the brain in the same manner as acupuncture, without being invasive. The effects of this stimulation outlast the treatment by hours or even days. Also, unlike TENS which has a fairly short treatment duration, ALTENS may be administered for as long as 30 minutes of a given treatment.

Table 1. TENS techniques

	Physiological intention	Clinical technique
Conventional TENS	Selective activation of A-beta nerve fibres eliciting segmental pain relief	Low-intensity/high-frequency  Apply at site of pain "Strong but comfortable TENS paraesthesiae" Use when in pain
Acupuncture-like TENS	Activation of A-delta nerve fibres leading to inhibition of C nerve fibres resulting in extra-segmental pain relief	High-intensity/low-frequency Apply to muscles, acupuncture point or trigger point "Strong but comfortable muscle contractions" Long duration; 15-30mins

Types of cancer pains & effectiveness of TENS:

Following on from our last post, you may be curious to know exactly what type of pain is experienced by palliative cancer patients and how effectively TENS reducing this pain. Simon (2008) listed the following as types of pain experienced by those in palliative care: bone pain, abdominal pain, neuropathic pain, rectal pain, muscle pain, bladder pain/spasm and pain of short duration. Of these types of pain, Simon (2008) only states TENS as a treatment option to relieve neuropathic pain. However, it was also noted that physiotherapy might be useful for muscle pain relief. Searle et. al (2009) conducted a case study and concluded from the findings that TENS may also be helpful in the relief of bone pain in cancer patients. The researchers also indicated ALTENS to be used as an alternate option to conventional TENS should it prove ineffective. However, ALTENS delivers a higher intensity dose than conventional TENS and as a result not all patients will be able to tolerate this treatment. In conclusion it is evident from these two research articles that TENS can be useful to cancer patients experiencing the described types of pain. Whilst it is not apparent from the evidence, that TENS relieves pain under all conditions, we are of the opinion that it should always be a viable option for palliative cancer sufferers as any pain relief is better than none.

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References
Jones, I. & M, Johnson. (2009). Transcutaneous electrical nerve stimulation. Continuing Education in Anaesthesia, Critical Care & Plan, 9(4), 130-135.

Searle, R. Bennett, M. Johnson, M. Callin, S. Radford, H. (2009) Transcutaneous Electrical Nerve Stimulation (TENS) for Cancer Bone Pain. Journal of Pain and Symptom Management, 37(3), 424-428.

Simon, C. (2008). Pain control in palliative care. InnovAiT, 1(4), 257-266.