Peripheral Nerve Stimulation Can Reverse Spinal Cord Injury Nerve Deterioration

A new study published in the Journal of Neurophysiology reports that peripheral nerve stimulation therapy can reverse spinal cord injury-associated nerve deterioration, potentially improving the benefits of current and emerging rehabilitation treatments.

Muscles contract when the nerves controlling them are activated by electrical impulses from the brain. The brain loses control of the muscles after spinal cord injury (SCI) because injured nerves do not excite easily or at all. In addition to the nerves in the spine, the peripheral nerves — nerves going to the limbs — downstream of the injury site are also compromised after SCI, worsening muscle atrophy and other health complications that follow the injury. This secondary nerve deterioration also limits the benefits of rehabilitation therapy and the possibility of spontaneous recovery.

According to the researchers, maintaining peripheral nerve function soon after SCI may lessen health complications and “lead to a better functional and rehabilitation outcome later on.” In this new study, the research team from The University of Sydney in Australia examined whether an intensive, short-term nerve stimulation treatment could improve peripheral nerve function after SCI.

Patients with SCI underwent 30 minutes of electrical nerve stimulation therapy five days a week for six weeks on one limb. The other limb remained untreated. All subjects started the therapy within six months of injury.

Patients with SCI had less excitable nerves with altered responses to electrical stimulation, indicating nerve dysfunction. After six weeks of therapy, the nerves in the treated limb responded to electrical stimulation more like nerves in healthy subjects. Nerve function in the untreated limb did not change over the six-week period.

“The present study has clearly demonstrated that an intensive six-week peripheral nerve stimulation program was beneficial in improving nerve excitability parameters toward the normal range,” the researchers wrote. Moreover, the improvements stayed if the patient continued with the stimulation therapy, they added.

According to the researchers, short-term peripheral nerve stimulation may be a new approach to preventing long-term changes in nerve and muscle function and improving rehabilitation outcomes. “Therapies that help to maintain peripheral nerve function, such as the peripheral nerve stimulation paradigm used in the current study, need to be incorporated into the mainstream neuro-rehabilitation program in the early phases of SCI,” the researchers wrote.

Shepherd Center director of spinal cord injury research Edelle Field-Fote, PT, Ph.D., FAPTA, says:  "This study adds to the long history of evidence to support the value of electrical stimulation to activate the nervous system. Nerve cells communicate with each other and with muscles through electrical signals, so using electrical stimulation is a way for us to communicate with the nervous system. Like any other system, the nervous system operates on the principle of 'Use it or lose it; use it and improve it."

Dr. Field-Fote points out that the Australian study shows the effects of electrical stimulation on the peripheral nerves -- the ones that connect the spinal cord to the muscle. The primary impact of SCI is on the central nerves -- those that travel in the spinal cord. Peripheral and central nerves respond very differently to therapies, she explains. For example, when a peripheral nerve is cut, it can regrow because the myelin that surrounds and insulates the nerve is produced by Schwann cells that contain growth-supporting factors. On the other hand, when a central nerve is cut, it does not regrow.

"There are many reasons for this, but one of the main reasons is that the myelin in the central nervous system is not produced by Schwann cells; instead, it is produced by oligodendrocytes," Dr. Field-Fote adds. "Oligodendrocytes in the central nervous system inhibit rather than promote growth. Electrical stimulation therapy is a common component of physical and occupational therapy, so this study is excellent support for the value of using electrical stimulation in physical and occupational therapy."

At Shepherd Center, ongoing research under way in the Hulse Spinal Cord Injury Lab is studying the effects of different types of stimulation on hand function, walking function and spasticity.

The Australian researchers' article “Short-term peripheral nerve stimulation ameliorates axonal dysfunction after spinal cord injury” is published in the Journal of Neurophysiology. It is highlighted as one of this month’s “best of the best” as part of the American Physiological Society’s APSselect program. Read all of this month’s selected research articles at http://apsselect.physiology.org/.