Why you should treat denervated muscle quickly
The European RISE study showed that complete lower motor neuron lesions resulting in denervated muscle could be successfully treated at home using a particular form of electrical stimulation. The project showed that both the muscle tissue quality and bulk could be rescued with regular use of this stimulation. We work with the Stimulette RISE which is direct outcome from this work and builds upon a significant amount of fundamental and applied research. In this article, we consider why starting such therapy early is beneficial and for whom.
What is Denervated Muscle?
Muscles that have lost their nerve supply can be found in a wide range of medical conditions, from severe autoimmune diseases to various trauma situations and stroke. We most commonly work with persons following a spinal cord injury, and where there is damage to the lower motor neurons, brachial plexus or a peripheral nerve.
The process of denervation is typical described as a progression through a number of chronological stages which after a number of years result in the involved muscle fibres transforming to a non-contractile mass of collagen and fat. Rather quickly following injury, there is a loss of electrically-induced tetanic contraction. In a matter of weeks, “conventional” neuromuscular stimulation with frequencies of up to 50Hz, pulsewidths of up to 500 microseconds and current up to 130 mA will not produce a muscle contraction.
So what should happen now? Left untreated, the involved muscles follow predictable stages with consequences for the ultimate trophic situation.
Whilst denervated muscles often lack the ability to actively contract, they can still influence the development of chronic medical conditions if left untreated.
In 1962, Ernest Gutmann edited “The Denervated Muscle” which for the first time brought together a major body of work on muscle denervation. It established the key issues involving the neurotrophic theory which was popular in the 1950’s and 60s. The research at this time was largely descriptive and considered both long term denervation and reinnervation. The interested reader could look at the article by Midrio (2006) who has reviewed the research of this era.
The effect of electrical stimulation was considered important in Gutmann’s view, but at that time the electrical stimulation protocols were unable to sustain or increase the muscle tissue. These days this is no longer the case and we know that certain protocols can be very effective and safe to use.
The risks of delaying
The reports from the RISE study, which focused on complete denervation, suggested that there is a “window of opportunity” within 18 months and certainly 3 years in which intervention with electrical stimulation can be expected to be successful within a reasonable period of time. What do we mean by success?
Whilst in the acute and sub-acute phase after injury to the lower motor neuron, the reasonable aim with this complete denervation group, can be to at least preserve the contractile tissue structure and bulk. Prevention of a breakdown of muscle structure is always going to be better than trying to salvage this later.
Early intervention with electrical stimulation is particularly important if reinnervation is expected or rescue surgery contemplated. There is also evidence that in the case of peripheral nerve injuries, electrical stimulation has a positive effect on nerve sprouting and neuroplasticity. It has been suggested that electrical stimulation of the nerve for 1 hour post operatively following nerve suture encourages the release of BNDF (brain dervied neurotrophic factor)
The preservation of tissue structure and bulk is still worthwhile where no reinnervation is expected because this will reduce the risk of long-term problems such as pressure ulcers on flaccid limbs, poor wound healing in response to tissue abrasions and generally compromised peripheral circulation. It is also the fact that many clients wish to have “normal” looking limbs that have shapely muscle.
How electrical stimulation is applied
We base our apporoach very much on the work reported intially from the RISE study and in subsequent papers by Helmut Kern and others. The clinical approach to the application of electrodes etc is covered nicely in an article by Ines Bersch-Porada in the new book referenced below. (Schick, T 2022)
As a rule of thumb we expect that 30 minutes of of stimulation will be needed per muscle group for 5 days per week.
The protocols used will typically involve a period of both twitch and tetanic induced contractions. Quite often, tetanic contractions cannot be produced intially but can be introduced after some months of regular application of twitch contractions.
Unlike commonly seen FES applications, the stimulation approach aims to work directly with muscle fibres in the affected muscle. The energy needed will involve using low frequency, long pulse duration (perhaps 200 ms), bipolar, rectangular waveforms and the electrodes used will need to cover as much of the muscle as possible. In cases of incomplete denervation or where there are innervated muscles alongside denervated ones we will sometimes modify the waveform shape to selectively activate the denervated muscles. We have described our approach in other blog articles.
As the time commitment to use electrical stimulation is significant, the user needs to understand clearly “what is in it for them?” Clarity of expectations and a realistic goal are important.
Conclusion
In our view, whether reinnervation is expect or not, early adoption of electrical stimulation is indicated for best results. Ideally during a stay in a spinal injury unit. Prevention of long-term trophic issues is the goal for complete injuries where reinnervation is not expected. With incomplete injury electrical stimulation can encourage neuroplasticity; especially when combined with functional exercise. If nerve surgery is contemplated, the structure and quality of muscle tissue can be preserved along with the expectation of better outcomes.
Reading
Midrio, M (2006) “The denervated muscle: facts and hypotheses. A historical review” Eur J Appl Physiol; 98 p 1-21
Kern, H et al (2010) “Home-based functional electrical stimulation rescues permanently denervated muscles in paraplegic patients with complete lower motor neuronlesion” Neurorehabilitation and Neural Repair; 24(8), p 709-721.
Ines Bersch-Porada “Electrical stimulaiton for improvement of function and muscle architecture in lower motor neuron lesions” In the Book “Function electrical stimulaton in neurorehabilitation - Synergy effects of technology and therapy” Edited by Thomas Schick. Springer 2022