Modification of cervical dystonia by selective sensory stimulation.

Cervical dystonia is often refractory to all forms of therapy. Many patients, however, are able to transiently abolish their spasms following a specific gesture that presumably enhances sensory input. Such observations prompted us to develop a protocol to determine if various forms of sensory stimulation could modify the motor control patterns in cervical dystonia. Surface EMG recordings of multiple neck and trunk muscles were obtained in 11 consecutive cervical dystonia patients. Baseline patterns of voluntary and involuntary muscle activation were established during a series of motor and non-motor tasks. The tasks were repeated during the application of vibratory or electrical stimulation to select muscle groups or to cutaneous and mixed nerves. Analysis of the results was made on the basis of paper and computer recordings of the data. Sensory stimulation decreased involuntary muscle activity and reduced spasms in 5 subjects. However, objective or subjective improvement usually occurred only after specific stimuli were applied to specific anatomical sites. In these cases, the protocol identified the site at which a specific sensory stimulus could be applied to control the dystonia. We conclude that selective sensory stimulation can beneficially modify cervical dystonia in some patients. Such findings warrant further investigation of the use of sensory stimulation for control of cervical dystonia.

Electrophrenic respiration in patients with craniocervical trauma.

We implanted electrophrenic respiration (EPR) units in 15 apneic quadriplegic patients with brain stem or high cervical cord injury. 11 of the patients achieved full-time respiration with EPR and another 2 achieved half-time respiration. Despite the loss of patients due to unrelated problems, 7 now use EPR continuously, 1 for 18 years. The factors involved in the significant success rate with EPR are discussed from the point of view of a neurosurgeon.

Electrophrenic respiration in patients with high quadriplegia.

After determining that 15 patients with high spinal cord injuries who were permanently apneic had viable phrenic nerves, electrophrenic respiration units were implanted. Thirteen of the patients (86%) achieved full-time respiration and two more achieved half-time respiration. Despite the loss of 8 patients to unrelated problems, 7 now use electrophrenic respiration continuously, one having done so for 16 years. The patient selection criteria, neurophysiological evaluation method, surgical procedure, postoperative care, and methods for diagnosis of system failures are presented. A comparison of the cervical and thoracic procedures is made. The cervical approach is preferred. Complications consisted primarily of equipment failures. For the external components there were several cases of antenna connection and battery connection failures. The implanted receivers failed in 6 cases with an average lifetime of 48 months, ranging from 24 to 108 months. In one case fibrosis around the electrode resulted in failure to stimulate the phrenic nerve effectively. In another case, infection required removal of the system which was reimplanted later and has continued to provide successful ventilation.

Cortical potentials evoked by epidural stimulation of the cervical and thoracic spinal cord in man.

Scalp somatosensory evoked potentials (SEPs) were recorded after electrical stimulation of the spinal cord in humans. Stimulating electrodes were placed at different vertebral levels of the epidural space over the midline of the posterior aspect of the spinal cord. The wave form of the response differed according to the level of the stimulating epidural electrodes. Cervical stimulation elicited an SEP very similar to that produced by stimulation of upper extremity nerves, e.g., bilateral median nerve SEP, but with a shorter latency. Epidural stimulation of the lower thoracic cord elicited an SEP similar to that produced by stimulation of lower extremity nerves. The results of upper thoracic stimulation appeared as a mixed upper and lower extremity type of SEP. The overall amplitudes of SEPs elicited by the epidural stimulation were higher than SEPs elicited by peripheral nerve stimulation. In 4 patients the CV along the spinal cord was calculated from the difference in latencies of the cortical responses to stimulation at two different vertebral levels. The CVs were in the range of 45-65 m/sec. The method was shown to be promising for future study of spinal cord dysfunctions.

Spinal cord stimulation for the control of spasticity in patients with chronic spinal cord injury: I. Clinical observations.

The effectiveness of spinal cord stimulation for control of spasticity was studied in 59 spinal cord injury patients. SCS was markedly or moderately effective in reducing spasticity in 63% of the patients. We found that control of spasticity by SCS was not correlated with the severity of spasticity, the type of spasticity (flexor or extensor), or the ability to ambulate. However, stimulation was more effective in patients with incomplete cervical lesions than in complete cervical lesions. Stimulation below the lesion was more effective than above. We conclude that SCS was effective when electrodes were properly positioned below the lesion over the posterior aspect of the spinal cord in patients with some residual spinal cord function. We hypothesize that SCS controls spasticity by modification of activity of spinal-brainstem-spinal loops and by suppression of segmental excitation through antidromic activation of propriospinal pathways.

Spinal cord stimulation for the control of spasticity in patients with chronic spinal cord injury: II. Neurophysiologic observations.

We sought neurophysiologic evidence that spinal cord stimulation could modify the behavior of spinal reflexes in 15 chronic SCI patients who showed the beneficial effect of SCS on spasticity. We studied the behavior of passive stretch, clonus, cutaneous touch, plantar reflex irradiation, and the response to the neck flexion reinforcement maneuver during spinal cord stimulation by use of surface PEMG recordings. Fifty-five percent of the responses were changed during spinal cord stimulation, but with widely varying patterns of response in individual patients. Exceptional patients showed changes in most or all responses; most showed changes in two or three. Thirty of seventy-five responses showed a reduction in motor unit activity in the recordings. Eleven of seventy-five responses were increased. Excessive stimulation strength enhanced spasticity in patients in whom another stimulus setting suppressed spasticity. We conclude that spinal cord stimulation could modify segmental reflexes but that the effects were selective, probably dependent on the preserved segmental structures and ascending and descending pathways.

Neurophysiological assessment of electrode placement in the spinal cord.

The use of neurophysiological techniques in addition to radiographic methods to determine the location of electrodes to be introduced into the epidural space for spinal cord stimulation is beneficial. Information on the distribution of paresthesias and muscle twitches provides an indication of the level and lateral location in relation to the midline of the spinal cord. For electrodes placed posteriorly, the threshold currents necessary for sensation are lower than those for muscle responses. Somatosensory evoked potentials resulting from epidural stimulation demonstrate effective depolarization of ascending structures. Evoked potentials recorded from the electrodes in response to peripheral nerve or spinal cord stimulation at a distant segment illustrate the possibility of activation of underlying generators of the spinal cord.

Remarks on spinal cord stimulation and the placebo effect.

Spinal cord stimulation, which has been shown to be beneficial in multiple sclerosis as well as in sustained spinal cord injury, works through modification of specific motor mechanisms. This modification occurs through regional recruitment of spinal cord activity in posterior aspects of the spinal cord. Substantial involvement of the placebo effect can be ruled out by noting the persistence of beneficial effects observed in spinal cord injury patients and by the fact that the effects are related only to depolarization of posterior structures of the spinal cord, rather than to perception of a 'tingling' sensation caused by spinal cord stimulation. Such a sensation can also occur when electrodes are over anterior or lateral structures of the spinal cord, when the stimulation is not effective in alleviating motor symptoms.

Clinical evaluation of the effect of spinal cord stimulation on motor performance in patients with upper motor neuron lesions.

The effect of chronic electrical stimulation of the spinal cord was evaluated in a group of 24 patients with multiple sclerosis, spinal cord injury, and degenerative disorders of the central nervous system. The systems for stimulation had been implanted from 12 to 30 months prior to completion of evaluation. At the time of completion of evaluation, 23 of the 24 patients still had implanted systems, although 6 of them had not used spinal cord stimulation because of no noticeable effect. In 3 patients stimulation had been disconnected because of technical failure of the system. In 1 patient the system had been removed 8 weeks after implantation because of inflammation in the under-skin receiver pocket. The effects on motor performance of the remaining 14 patients who had continuously active systems were improved bladder control, diminished spasticity, improved movement coordination, and increased endurance.

Technological problems of spinal cord stimulation systems: a clinical perspective.

Technological problems of spinal cord stimulation, from the clinician's standpoint are the topics of this review of a round table discussion. Surgical aspects of spinal cord stimulation system implant procedures are reviewed. Safety and reliability of the methods and systems are discussed. Problems with durability and fixation of epidural electrodes are reported, and solutions are sought from the continued interaction of clinicians and biomedical engineers in the future development of methods and systems.

Biomedical engineering specifications for epidural spinal cord stimulation to augment motor performance.

Stimulating electrodes were placed in the posterior portion of the epidural space in the upper thoracic spinal region in 28 patients with upper motor neuron disorders. Parameters of stimulation commonly used for chronic stimulation were a 200 microsecond pulse width, 22 Hz repetition rate, and 5 ma amplitude. Using a 16 gauge Touhy needle, platinum electrodes were passed between the posterior vertebral processes into and up the spinal epidural space to upper thoracic locations. Passive implanted receivers, powered and controlled by external RF transmitter/pulse-generator devices, were employed to provide the stimulus current to the electrodes. A description of available systems, problems and diagnosis of problems, and future directions is presented. This is based on studies in patients with stimulation systems implanted for more than six months.

Study of sensation and muscle twitch responses to spinal cord stimulation.

Electrically induced sensation and muscle twitches were studied in a group of 43 patients in whom epidural electrodes were percutaneously placed for the evaluation of the effect of spinal cord stimulation on modification of their impaired motor control. Mean stimulus strength for sensory threshold was 5.25 +/- 2.75 mA and the tolerance level was at the stimulus strength of 10.8 +/- 4.4 mA. Muscle twitches with short latencies were recorded in limb and trunk muscles within the segments at the stimulating cathode. Exceptionally, higher stimuli elicited muscle twitches of distant segments.