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Keywords:

  • horse;
  • electroacupuncture;
  • acupuncture;
  • nerve injury;
  • transcutaneous electrical nerve stimulation;
  • electrical stimulation;
  • nerve regeneration

The case report from de Fourmestraux et al. (2014) describes the use of electroacupuncture (EA) in the treatment of a facial nerve paralysis occurring as a post anaesthetic complication in a horse. It was applied in addition to conventional treatment in an effort to maximise the chances of recovery of nerve function. Nerve trauma with varying degrees of nerve deficit and associated pain are not uncommon in the horse. There are many indications and opportunities for EA to improve the outcome of injuries involving nerve damage, and there is good evidence from clinical and experimental trials in other species in the use of EA for these cases.

A recent review of the EA literature through PubMed gives an account of the breadth of research in this area from 1975 to 2012 (Mayor 2013). This found 548 clinical studies of EA in man and 1607 predominantly experimental animal studies. These were mainly pain studies investigating endogenous opioid mechanisms. More recently, nonpain studies dominate. The findings support the upregulation of β-endorphins occurring in the brain from low frequency EA (1–7 Hz) and the upregulation of dynorphin in the spinal cord occurring from high frequency EA (15–100 Hz). Electroacupuncture delivers a stronger dose of acupuncture, more effectively upregulates the endogenous opioid mechanisms, and is more easily standardised for research purposes than manual acupuncture.

Peripheral nerve injuries result in partial or total loss of motor, sensory, and autonomic functions in the denervated area due to the interruption of axons, degeneration of distal nerve fibres, and eventual death of axotomised neurons (Allodi et al. 2012). Deficits can be compensated by regenerating injured axons or by collateral branching of undamaged axons, and remodelling of nervous system circuitry related to the lost functions. Plasticity of central connections may compensate functionally for the lack of adequate target reinnervation; however, plasticity has limited effects on disturbed sensory localisation or fine motor control after injuries, and may even result in maladaptive changes, such as neuropathic pain and hyper-reflexia (Navarro 2009). The lack of specificity of nerve regeneration, in terms of motor and sensory axon regrowth, pathfinding and target reinnervation, is one of the main shortcomings for recovery.

Peripheral nerve regeneration has been extensively studied in function and gene expression using a sciatic nerve crush model in mice and rats (Vogelaar et al. 2004). Recovery of sensory and some motor function occurred in approximately 3 weeks; however, with the return of sensory function, a state of mechanical allodynia (painful experience generated by non-noxious stimuli) develops and is slow to retreat. This is a component of neuropathic pain known to exist in man and studied in laboratory animals, but only relatively recently considered as a source of chronic pain in horses (Graf von Schweinitz 1999; Macgregor and Graf von Schweinitz 2006; Jones et al. 2007; Driessen et al. 2010; Muir 2010). Considering the risks of neuropathic pain from peripheral nerve injury it is interesting to note the ongoing efforts to treat idiopathic headshaking in the horse by compression of the infraorbital nerve, which has a reported initial success rate of 63%, post operative nose rubbing rate of 63%, and symptom recurrence rate of 26% (Roberts et al. 2013).

Different therapies have evolved to improve recovery from nerve injury including exercise, and electrical stimulation, but the functional outcome of nerve repair can still be disappointing due to muscle atrophy, scar tissue, neuroma, disturbed sensory evolution, and poor motor control. Average axonal regeneration rate in mammals is 1–3 mm/day (Gordon et al. 2009) and the length of nerve damage in the horse may easily be several centimetres leading to a lengthy regeneration time with increased risks of unsatisfactory regeneration.

Electrical stimulation has shown positive results on peripheral nerve regeneration effects in laboratory animals, mostly using EA with implanted electrodes with different electrical parameters: weak constant direct current and pulsed alternating current (Pomeranz et al. 1984; McDevitt et al. 1987; Beveridge and Politis 1988; Pomeranz and Campbell 1993; Chen et al. 2001; Inoue et al. 2003; Mendonça et al. 2003). One of the emerging links of EA being investigated is with the modulation of nerve growth factor in nerve repair (Manni et al. 2011).

In a study of rats with transected median nerves one group received plain acupuncture for 15 min every 2 days from one week after injury using points (PC 3 and 7) near the proximal and distal nerve stumps; another group received EA (1 mA at 2 Hz) to produce a visual muscle contraction; a third group were untreated controls (Ho et al. 2013). Both treatment groups had better morphological, electrophysiological and functional outcomes than the control group.

Not all electrical stimulation forms are helpful. Some studies of electrical stimulation have also had negative outcomes illustrating that the intensity and frequency of the electrical field plays an important role (Aydin et al. 2006). An investigation of transcutaneous electrical stimulation with low (4 Hz) and high (100 Hz) frequency transcutaneous electrical nerve stimulation (TENS) was undertaken as this technique is frequently employed to control neuropathic pain (Baptista et al. 2008). Using mice with a sciatic crush lesion treated 30 min daily, TENS 5 days/week for 5 weeks led to a delayed regeneration with negative morphological changes of nerve tissue compared to an untreated control group, especially in the high frequency TENS group. The timing of the application of EA after nerve injury also appears to be an important factor (Yeh et al. 2010). In rats subjected to sciatic nerve section, those treated 8 days or 15 days later with low frequency (2 Hz at 1 mA) EA for 15 min every other day for 2 weeks had significantly improved nerve regeneration, which was not the case in the group treated from the first day.

Similarly, exercise has been shown to be a positive or negative factor in nerve regeneration investigations dependent on the exercise intensity and stress caused to the animal (van Meeteren et al. 1998). Recently, low energy extracorporeal shock wave treatment has been shown to accelerate the recovery of muscle sensitivity and function by promoting regeneration after nerve compression injury in rats (Hausner et al. 2012; Mense and Hoheisel 2013). This still requires work to determine the appropriate dose and frequency of treatment before it can be confidently used in the horse.

In the case report from de Fourmestraux et al. (2014), care was taken to select appropriate points and electrical stimulation properties based on the research, and to include an exercise tailored to the condition to optimise the chances for recovery. The significance being that it is possible to treat inappropriately, cause additional harm, and bring about a negative outcome from the use of EA. Similar case reports are lacking in the literature and hopefully this report will encourage similar ones.

A case report of acupuncture in a dog with idiopathic facial nerve paralysis makes an interesting comparison (Jeong et al. 2001). A terrier with a 35 day acute onset of unilateral facial nerve paralysis and no improvement on daily prednisolone at 1 mg/kg bwt was treated with dry needle acupuncture. Points on the face (LI 20, ST 2, ST 7, SI 18, TH 17 and GB 3) were needled only on the contralateral side, and a distal forelimb and a hindlimb point was treated bilaterally (LI 4 and GB 34 respectively) for 20 min every other day for the first week, then weekly for the next 3 weeks. Lip drooping and drooling were abolished after the first treatment, with progress to complete facial symmetry achieved by the last treatment. In this case there was no local stimulation on the affected side indicating central neural reflexes and mechanisms were responsible for the improvements. Studies of neuropathic mechanisms from nerve injury demonstrate a unilateral injury often progresses to bilateral neuropathic changes (Behera et al. 2013); interestingly, acupuncture treatment on the contralateral side has been shown to treat the opposite side (Kim et al. 2010).

The use of EA in nerve regeneration in man has been reported, e.g. in carpal tunnel syndrome with severe axon degeneration and release surgery (Gordon et al. 2008). Trains of 20 Hz electrical stimulation for one hour to 2 weeks accelerated axon outgrowth across the suture site in association with elevated neuronal neurotrophic factor and receptors and promoted the full reinnervation of thenar muscles in contrast to a nonsignificant increase in motor unit numbers in the control group.

Some critics may take issue with this example as not representing acupuncture because of a lack of adherence to the traditional Chinese medicine language of yin and yang, and the flow of Qi, and one may then consider this an example of western medical acupuncture. Acupuncture has historically evolved and traditional Chinese medicine is arguably grossly misrepresented by translation errors of the ancient Chinese texts and the politics of the practice from lay practitioners (Birch and Felt 1999; Kendall 2002 Unschuld 2003; Schnorrenberger 2011). The advances in neuroscience have brought an increasing amount of evidence for the usefulness and relatively low risks in a competent application of acupuncture including the more modern forms of EA and laser acupuncture. More evidence in the form of controlled trials and clinical trials are required, but this can equally be applied to most of veterinary medicine.

Author's declaration of interests

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  2. Author's declaration of interests
  3. References

No conflicts of interest have been declared.

References

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  2. Author's declaration of interests
  3. References
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