TRANSCRANIAL MAGNETIC STIMULATION (TCMS) IN REHABILITATION
J.C. ROTHWELL, MRC, Human Movement & Balance Unit, Institute of Neurology Queen Square, London WC1N 3BG, UK.
TCMS in patients shortly after stroke has shown a useful correlation between the presence of EMG responses in the likelihood of good recovery. Although functional imaging studies show activation of the ipsilateral cortex during movement of the affected hand in recovered stroke, there is little evidence from TCMS of the development of large diameter projections from the damaged hemisphere which could account for this activation. The situation is different in more proximal muscles. TMS can activate upper oesophagus and pharynx. They are innervated bilaterally, although in most subjects, one or other hemisphere seems to be dominant, unrelated to handedness. Dysphagia after hemispheric stroke seems to occur only if damage affects the hemisphere with the dominant oesophagus/pharyngeal projection. Recovery from dysphagia is often evident at around 3 months post stroke. In such cases TCMS gives clear evidence of increased excitability of the remaining projection from the undamaged hemisphere. Finally, we have shown in normal subjects that the excitability of the cortical pathway to the pharynx can be increased for up to 30 minutes following continuous electrical stimulation of the pharynx for 10 minutes. Treatment with continuous afferent stimulation may therefore be a possible mechanism of accelerating the changes in the ipsilateral hemisphere after stroke.
THE PHYSIOANATOMICAL CHARACTERISTICS OF SHORT LATENCY SOMATOSENSORY EVOKED POTENTIALS FOLLOWING STIMULATION OF THE MEDIAN NERVE
Tohru Yamada, MD (University of Iowa, Iowa City, Iowa U.S.A.)
The short latency median nerve somatosensory evoked potentials (SSEP) consists of multiple components having characteristics of far-field, stationary field and near-field potentials. They are P9, N9, N1O, P11, N11, N13, P13, P14, N14, N18, N20 and P20/ P22. Two components having the same latency with opposite or same polarity may or may not be of the same origins. For example, P9 far-field potential recorded from the scalp and N9 stationary field potentials recorded from the stimulated are of the same origin, whereas P13 far-field potential from the scald and N13 negative potential from the neck arise from separate generators, i.e. P13 arising from brainstem and N13 from cervical cord. Further, N13 from the high and low cervical regions are now considered to have separate origins. Because of intricate mixture of these potentials within short time domain, a given component may be abolished or enhanced depending on the electrode derivations. Also inappropriate use of electrode derivation may lead to erroneous identification of peak of interest. Understanding of physiological characteristics and field distribution of each component is important to accurately delineate these potentials.
ELECTRODIAGNOSIS IN REHABILITATION MEDICINE
Murray E. Brandstater (Loma Linda University, Loma Linda, CA, USA)
Many of the patients treated by physicians in physical medicine and rehabilitation have neuromuscular disorders. The information provided by electrodiagnosis in these patients is essential for the physician to provide optimal patient care. This paper will describe how the electrodiagnostic evaluation can assist the physician in making the diagnosis and in guiding subsequent treatment.
(1) The initial study. Information from the initial study helps to establish the diagnosis. In addition, careful examination of the electrodiagnostic data may reveal the severity of the disease process, and may indicate its acuteness or chronicity. The information can assist the physician in making a prognosis.
(2) Follow-up study. When patients are seen for follow-up examination, the data give information about progression of the disease, or recovery, and may be quite helpful in monitoring the response to treatment. Statements about prognosis can be refined. All of these points will be illustrated with examples.