Electrical stimulation of the spinal cord is a promising strategy for reestablishing walking after spinal cord injury, recent studies show. But for patients suffering from muscle spasms, the stimulation protocols have a limited effect due to the unpredictable behaviour of involuntary muscle stiffness related to spasticity. Muscle spasticity affects almost 70% of spinal cord injured patients
Now, scientists at EPFL, Università San Raffaele and Scuola Sant'Anna have found a promising way to address and reduce muscle spasticity in patients with incomplete spinal cord injury. It involves zapping the spinal cord with high-frequency electrical stimulation that blocks the abnormal muscular contractions. This high-frequency treatment gives patients suffering from spasticity access to rehabilitation protocols that were previously inaccessible to them with a very good clinical outcome. The results are published today in Science Translational Medicine.
"We've found that high frequency electrical stimulation of the spinal cord, coupled with the usual continuous, low-frequency spinal stimulation, is effective during rehabilitation after spinal cord injury, overcoming muscular stiffness and spasms in paralyzed patients and effectively assisting the patients during locomotion," explains Silvestro Micera, professor at EPFL's Neuro X Institute and Scuola Sant'Anna.
"This is a safe and effective surgical procedure that offers a new perspective in the treatment of patients with severe damage to the spinal cord. We are planning to extend the indications to different clinical conditions we will define in the next month. We are deeply grateful to the patients who trusted us," says Pietro Mortini, Head of the Neurosurgery and Stereotactic Radiosurgery Unit at IRCCS Ospedale San Raffaele (Milan) and full professor of Neurosurgery at the University Vita-Salute San Raffaele.
Electrical stimulation of the spinal cord is an indirect way to reach the motor neurons that make muscles move. That's because the backside of the spinal cord contains sensory neurons which in turn communicate with the motor neurons. In muscle
spasticity, it is known that the spinal sensory-motor circuits are overreactive. In fact, the spinal cord is naturally overreactive to stimuli, which is good since it leads to fast reflexes. Normally, that over-reactivity is balanced out by the brain that inhibits the motor circuits. In spinal cord injury, the patient loses messaging from the brain and these inhibitory mechanisms. By indirectly stimulating the motor circuits, the research team has found that high-frequency stimulation of the spinal cord is an artificial and safe way to inhibit that over-reactivity without producing discomfort in patients.
During the clinical trial at San Raffaele Hospital, coordinated by Mortini and Micera, Simone Romeni, first author of the study and researcher at EPFL and Università San Raffaele, proposed to implement high-frequency stimulation taking inspiration from previous work on high-frequency kilohertz blocks of motor circuits by stimulating peripheral nerves.
"At this stage, we can only speculate that high-frequency stimulation acts as a kilohertz block that prevents muscle spasticity," says Micera.
"The clinical data with the two patients point to the benefits of implementing high-frequency stimulation for reducing muscle stiffness and spasms in paralysis. More experiments will be necessary to confirm the potentials of this approach," concludes Mortini.
