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Interferential therapy: could it be more effective than TENS in the management of MS-related symptoms?

Dr Gareth Noble
School of Health Science, Swansea University

Way Ahead 2006;10(4):8-10


Introduction

Neurological conditions have a high prevalence within the UK, with approximately 10 million people determined to be living with a long-term chronic neurological condition[1]. Multiple sclerosis (MS) is one of the most common neurological conditions with approximately 85,000 people living with the condition[2]. People with a neurological condition, such as MS, present with a range of symptoms including:

  • physical and motor problems (gait abnormalities, fatigue, muscle weakness);
  • alterations in sensation (vision, hearing, pain);
  • cognitive behavioural problems (memory lapse, confusion);
  • communication problems (verbal and written);
  • psychosocial/emotional effects (depression, loss of self-image).

Each of these dimensions requires specialist care and rehabilitation from a wide range of healthcare professionals, such as clinical psychologists, nurses, physiotherapists, occupational therapists, speech and language therapists[1].

Within the field of rehabilitation medicine, the physiotherapist has a number of treatment techniques at their disposal and one of the mainstays is the application of therapeutic electrical currents (mainly, transcutaneous electrical nerve stimulation (TENS) and interferential therapy (IFT)). Essentially, the basis for the clinical use of electrotherapy is related to the various pain modulation theories[3]:

  • gate control theory by Melzach and Wall[4] proposes that the selective activation of large diameter nerve fibres (A-beta) which conduct a nerve impulse faster than the smaller diameter pain fibres (A-delta and C fibres) will close the 'gate' within the spinal cord that allows the nociceptive (pain) impulse to be relayed to the higher centres in the brain;
  • descending pain inhibition pathways (including the inducement of endogenous opiate release, which are the body's naturally occurring form of morphine);
  • physiological block of a nerve impulse, thus stopping any painful stimulus from travelling the peripheral nerve system, which results in that nociceptive impulse not being interpreted as being painful by the brain;
  • vasodilation to remove the chemical irritants that initiate the pain episode;
  • placebo effect.

TENS are units that deliver low frequency currents mainly for the management of pain. They deliver currents with a frequency of less than 250Hz, which is within the biological range of skin resistance and therefore, results in a superficial level of stimulation[5]. For the current to penetrate the skin more deeply, greater intensity is needed, which can cause pain and discomfort. In contrast to TENS, IFT currents are created by the 'interference' effects of two alternating medium frequency currents, which mean they are not impeded by skin resistance. When two differing currents are applied simultaneously to the tissues through interrelated electrodes, an oscillation is generated endogenously where they augment to create a new low frequency current deep within the targeted tissues (eg if current one is 4000Hz and the other is 4100Hz it would result in a 100Hz current)[6].

diagram showing how two differing currents are applied simultaneously to the tissues through interrelated electrodes
If current A - A is at 4000Hz and current B - B is at 4100Hz then the interference current will have a 'beat frequency' of 100Hz

An additional treatment choice is to have the modulated frequency delivered at either 'constant' or 'rhythmical' modes. At the constant setting, the interferential unit generates a single constant frequency (eg 100Hz), which can be selected by the therapist. The rhythmical setting allows the therapist to select any frequency range (eg 10-100Hz) in which the actual interferential current continuously changes between the selected limiting values. It has been suggested that this situation is more beneficial in the clinical application of this modality, as it facilitates the selection of an optimal frequency to selectively activate one of the pain theories[7].

IFT and TENS are often viewed as the same form of treatment, but I would argue that they are two distinctly different treatment options that have different electrophysical properties (ie waveform and frequencies), produce different physiological effects and therefore, could have different clinical outcomes. As a consequence, the research evidence for TENS should not be applied to IFT, even though the majority of research into electrotherapy focuses on TENS. Furthermore, literature reports that IFT is more commonly used within clinical practice for the treatment of various conditions, specifically for musculoskeletal pain[8-10]. However, clinical based investigations to support its continued use are limited[5,11,12].


MS-related pain

For people living with MS, pain is reported as one of the most common symptoms, with a prevalence rate of between 58-85%. Additionally, pain levels have been demonstrated to correspond directly to limitations in physical functioning as well as mental health problems[13]. Osterberg et al[14] conducted a study to examine the prevalence of central pain in people with MS and reported that the majority of participants had pain in the lower (87%) and upper (31%) extremities. Additionally, Archibald et al[15] indicated that 53.3% presented with head pain, 57.8% with arm pain, 73.3% with leg pain and 48.9% with trunk pain.

A number of treatment options can be used in the management of pain, ranging from pharmacological to non-pharmacological complementary therapies. In the case of a complex condition, such as MS, it is necessary to use a multidisciplinary approach to pain utilising the expertise of medics and clinical therapists. As the MS Society[16] reports, the pharmacological management of MS-related pain cannot be used exclusively due to the need to balance adverse reactions and drug availability. Therefore, they advocate the use of adjunctive therapies delivered by physiotherapy to supplement the prescribed medications, such as electrotherapy.

However, several authors have indicated the scarcity of empirical evidence for IFT[12,17,18]. Previous laboratory based studies have demonstrated the potential of IFT to produce pain relief[3,6,19], but others have failed to support the use of IFT in pain management[20,21]. To add to the disparity of evidence, very few clinically based studies have specifically examined the effectiveness of IFT in any condition. In 1999, Werners[22] conducted a randomised trial comparing IFT against motorised lumbar traction with massage in the management of low back pain, using 152 participants. The authors concluded that despite the progressive reduction in disability score, there was no significant difference between the two treatments. A finding supported by Hurley et al[23] who compared IFT with manipulative therapy to the sole application of IFT in a randomised clinical trial using 240 participants, which demonstrated no significant difference between treatments. However, the authors did report that IFT reduced functional disability, pain and increased quality of life scores. Jarit et al.[24] investigated the effects of home based IFT treatment on postoperative pain, oedema and range of motion of the knee using 87 participants and concluded that IFT may help reduce pain, pain medication taken and oedema. To date, there are no published clinical trials that have examined directly the hypoalgesic effects of IFT upon MS-related pain. However, a previous research study has examined the potential of TENS to reduce the experience of low back pain in people with MS in a pilot study[25]. This study, using only 15 people, examined TENS being applied for 45 minutes, three times per week for a period of six weeks. The treatment parameters used were 4Hz, 110Hz and a placebo group. The results indicated that despite there being no statistically significant effect, both the active TENS groups showed a trend of improvement that was greater than the placebo group, indicating the potential of electrotherapy to produce a pain relieving effect.

An IFT machine in use
An IFT machine in use
Picture courtesy of Enraf Nonius BV


Other MS-related symptoms

It could be postulated that due to these characteristics (specifically deep penetration of the therapeutic current) and what is currently known about muscle physiology, IFT could have the potential to be effective in pain management (via the pain modulation theories) and for the management of fatigue, muscle weakness, muscle spasms and walking pattern (gait), as the electrical current may have the potential to change muscle fibre type from fatigable to fatigue resistant[26]. These are symptoms that have been closely associated with a reduction in physical functioning and quality of life for people with MS.

However, the precise mechanism of neurologically-related fatigue is not fully understood and subsequently, available treatments are limited[27,28]. Currently, it is thought that the feeling of constant exhaustion is a characteristic of central fatigue, which is conceptually defined using the physiological premise that work output (ie muscle power) of voluntary muscle activity depends on the applied voluntary effort, which is controlled by motivational input and perceived effort via feedback from motor, sensory and cognitive systems[27]. Hence, if it were possible to alter either motivational (cognitive functioning), neural (sensory) or motor (ie muscle activity) input levels, it could be postulated that any intervention based on any of these three principles could be effective in managing the effects of fatigue. Therefore, this forms the basis for either a cognitive behavioural or physical activity approach to effectively manage the effects of neurologically-related fatigue. Could the application of a modality that has the ability to provide a sensory and motor input, such as IFT, be effective?


Conclusions

Despite over 50 years of clinical application of electrotherapy (in particular IFT), questions still remain. It has been suggested that each of the pain theories outlined previously can be selectively activated by applying different current frequencies (for example, 100Hz or above will activate the A-beta fibres to close the pain gate in the dorsal horn in the spine; whilst a low frequency (10Hz or below) will activate the release of endogenous opiates)[5]. The question is how do they do that? What aspect of the electrical current (frequency, pulse duration, or wave form) has the greatest influence upon efficacy? Furthermore, what are the optimal treatment parameters (frequency, electrode placement, length of treatment time) that would facilitate the selective activation of different nerve fibre types to close the pain gate or induce the release of endogenous opiates? Additionally, with the case of MS, where there is a degenerative process removing the myelin sheath covering a nerve, thus changing the characteristics of the nerves' how would this affect how electrotherapy is able to do what the theory suggests? These questions are at the heart of any research into the clinical application of electrotherapy, but when you include the current funding crisis within the NHS and the need to be able to justify service delivery in terms of its evidence base; there is a desperate need for robust research to provide the evidence to determine whether or not electrotherapy is effective clinically. Despite this, we should remember that the anecdotal evidence does suggest that electrotherapy (TENS or IFT) has the potential to be a highly effective therapy for people with MS.


References

  1. Department of Health.
    National Service Framework for Long-term Conditions.
    London: Department of Health; 2005.
  2. Ko Ko C.
    Effectiveness of rehabilitation for multiple sclerosis.
    Clin Rehabil 1999;13(suppl 1): 33-41.
  3. Noble JG, Henderson G, Cramp AF, et al.
    Effect of interferential therapy upon cutaneous blood flow in humans.
    Clin Physiol 2000; 20(1): 2-7.
  4. Melzack R, Wall PD.
    Pain mechanisms: a new theory.
    Science 1965; 150(699):971-979.
  5. Noble JG, Walsh DM, Lowe AS.
    Interferential Therapy Review: Part 1.Mechanism of action and clinical usage.
    Phys Ther Rev 2000; 5: 239-245.
  6. Noble JG.
    Interferential therapy – an assessment of its hypoalgesic and neurophysiological effects.
    DPhil Thesis: University of Ulster; 2000.
  7. DeDomenico G.
    New dimensions in interferential therapy. A theoretical and clinical guide.
    Reid Medical Books: Linfield; 1987.
  8. Lindsay D, Dearness J, McGinley C.
    Electrotherapy usage trends in private physiotherapy practice in Alberta.
    Physiother Can 1995; 47(1): 30-34.
  9. Pope G, Mockett S, Wright J.
    A survey of electrotherapeutic modalities: ownership and use in the NHS in England.
    Physiotherapy 1995; 81(2): 82-91.
  10. Robertson V, Spurritt D.
    Electrophysical agents: implications of their availability and use in undergraduate clinical placements.
    Physiotherapy 1998; 84: 335-44.
  11. Watson T.
    The role of electrotherapy in contemporary physiotherapy practice.
    Man Ther 2000; 5(3): 132-141.
  12. Noble JG, Walsh DM, Lowe AS.
    Interferential Therapy Review. Part 2.Experimental pain models and neurophysiological effect of electrical stimulation.
    Phys Ther Rev 2001; 6: 17-38.
  13. Scherder E, Wolters E, Polman C, et al.
    Pain in Parkinson's disease and multiple sclerosis: its relation to the medial and lateral pain systems.
    Neurosci Biobehav Rev 2005; 29(7):1047-1056.
  14. Osterberg A, Boivie J, Thuomas KA.
    Central pain in multiple sclerosis – prevalence and clinical characteristics.
    Eur J Pain 2005; 9(5): 531-542.
  15. Archibald CJ, McGrath PJ, Ritvo PG, et al.
    Pain prevalence, severity and impact in a clinic sample of multiple sclerosis patients.
    Pain 1994; 58(1): 89-93.
  16. MS Society of Great Britain and NI.
    MS Essentials – Pain and Sensory Symptoms.
    London: MS Society; 2006.
  17. Johnson M.
    The mystique of interferential currents when used to manage pain.
    Physiotherapy 1999; 85(6): 294-297.
  18. Alves-Guerreiro J, Noble JG, Walsh DM, Lowe AS.
    The effect of three electrotherapeutic modalities upon peripheral nerve conduction and mechanical pain threshold.
    Clin Physiol 2003; 21(6):704-711.
  19. Jorge S, Parada CA, Ferreira SH, Tambeli CH.
    Interferential therapy produces antinociception during application in various models of inflammatory pain.
    Phys Ther 2006; 86(6): 800-808.
  20. Cramp AFL, Noble JG, Allen JM, et al.
    A controlled study on the effects of transcutaneous electrical nerve stimulation and interferential therapy upon the RIII nociceptive and H-reflexes in humans.
    Arch Phys Med Rehabil 2000; 81: 324-333.
  21. Minder PM, Noble JG, Alves-Guerreiro J, et al.
    Interferential therapy: lack of effect upon experimentally induced delayed onset muscle soreness.
    Clin Physiol Funct Imaging 2002; 22(5): 339-347.
  22. Werners R, Pynsent PB, Bulstrode CJK.
    Randomised trial comparing interferential therapy with motorised lumbar traction and massage in the management of low back pain in a primary care setting.
    Spine 1999; 24(15):1579-1584.
  23. Hurley DA, McDonough SM, Dempster M, Moore AP, Baxter GD.
    A randomised trial of manipulative therapy and interferential therapy for acute low back pain.
    Spine 2004; 29(20): 2207-2216.
  24. Jarit GJ, Mohr KJ, Waller R, Glousman RE.
    The effects of home interferential therapy on post-operative pain, edema, and range of motion of the knee.
    Clin J Sport Med 2003; 13(1): 16-20.
  25. Al-Smadi J, Warke K, Wilson I, et al.
    A pilot investigation of the hypoalgesic effects of transcutaneous electrical nerve stimulation upon low back pain in people with multiple sclerosis.
    Clin Rehabil 2003; 17(7):742-749.
  26. Ward AR, Robertson VJ.
    The variation in fatigue rate with frequency using kHz frequency alternating current.
    Med Eng Phys 2000; 22(9): 637-646.
  27. Chaudhuri A, Behan P.
    Fatigue in neurological disorders.
    Lancet 2004;363(9413): 978-988.
  28. Schreurs KMG, de Ridder DTD, Bensing JM.
    Fatigue in multiple sclerosis. Reciprocal relationships with physical disabilities and depression.
    J Psychosom Res 2002; 53(3): 775-781.

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