Continuous spinal cord electrical stimulation led to improvement in upper limb strength, motor control, and function among 2 patients with poststroke hemiparesis. However, only some of these abilities were retained without stimulation after the study ended. These are the findings of a small study published in the journal Nature Medicine.
Among individuals who experience a stroke, close to 75% will exhibit persistent deficits in motor control of their arm and hand, which are due, in part, to the failure of current neurorehabilitation approaches to significantly reduce upper limb impairment. Patients with chronic stroke exhibit a stereotypical motor syndrome of the upper limb that can be divided into quantifiable deficits:
- loss of strength;
- reduction in dexterity;
- intrusion of aberrant synergies; and
- disorders of muscle tone.
Among patients with stroke, this “paresis” phenotype has thus emerged from damage to the corticospinal tract (CST), disrupting connections between the cortex and the cervical spinal circuits that are responsible for control of arm and hand movements.
Since most cases of stroke damage to the CST are incomplete, researchers hypothesized that “voluntary motor control could be restored by amplifying the capacity of the residual CST.” In particular, they posited that “modulating the excitability of intact sublesional spinal circuits would increase their responsiveness to remaining CST neurons, thereby restoring the ability of these supraspinal inputs to drive movement.”
The current ongoing pilot study (ClinicalTrials.gov Identifier: NCT04512690) reports on results from the first 2 participants who had experienced a stroke and in whom electrical stimulation of the cervical spinal circuits was utilized to facilitate motor control of the arm and hand in chronic poststroke hemiparesis.
The first patient was a 31-year-old woman who had experienced a right thalamic hemorrhagic stroke secondary to a cavernous malformation 9 years prior to study participation. The second patient was a 47-year-old woman who had experienced a right ischemic middle cerebral artery (MCA) stroke secondary to a right carotid dissection, which created a large MCA territory infarct 3 years prior to study participation. In both of the participants, extensive damage to the CST was associated with chronic upper limb impairment.
Researchers sought to evaluate whether electrical stimulation of the cervical spinal cord can activate muscles of the arm of the hand in individuals who experience hemiplegia after a stroke. A surgical procedure was performed in each participant in which a system was implanted that provides epidural electrical stimulation (EES) to the cervical spinal cord. The ability of the EES to engage arm and hand muscles, as well as to produce distinct kinematic movements, was then computed.
The current pilot study was designed to calculate the immediate assistive effects of continuous SCS on poststroke motor deficits, including the following:
- muscle weakness;
- impairments in the dexterity of arm and finger movements;
- intrusion of aberrant flexor synergies; and
- abnormal tone.
The focus was on the measurement of immediate improvements that were attributable to the direct impact of SCS in facilitation of motor function in the arm and hand. Testing was initiated 4 days following implantation of the SCS leads and continued for 4 weeks. During this time, the participants underwent evaluation sessions 5 times per week, each of which lasted about 4 hours per day. The percutaneous leads were removed after 29 days.
Researchers found that continuous stimulation through selected contacts was associated with the following improvements:
Strength: grip force +40% in the first participant and +108% in the second participant;
Kinematics: +30% to 40% speed; and
These improvements enabled the 2 participants to perform movements that they were unable to carry out without spinal cord stimulation. Both of the participants were able to retain some of these improvements without any stimulation. There were no serious adverse events reported in either patient.
The key limitation of this study is the fact that the results are presented for only 2 participants, thus preventing any definitive conclusions to be drawn regarding safety and efficacy. Absence of a protocol based upper limb behavioral intervention and the short 4-week duration of the study may have decreased the amount of recovery that the participants could experience.
According to the researchers, “While we cannot conclusively evaluate safety and efficacy from two participants, our data provide promising, albeit preliminary, evidence that spinal cord stimulation could be an assistive as well as a restorative approach for upper limb recovery after stroke.”
Disclosure: Some of the study authors have declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.
Powell MP, Verma N, Sorensen E, et al. Epidural stimulation of the cervical spinal cord for post-stroke upper-limb paresis. Nat Med. Published online February 20, 2023. doi:10.1038/s41591-022-02202-6