Andrei V. Chistyakov

Preliminary evidence for a beneficial effect of low‐frequency, repetitive transcranial magnetic stimulation in patients with major depression and schizophrenia

This study was designed to evaluate the potential efficacy of repetitive transcranial magnetic stimulation (rTMS) at low‐frequency in patients with major depression and schizophrenia. Experimental Design: We investigated the therapeutic effect of a course of 10 rTMS sessions in 14 subjects with major depression (MD) and 10 with schizophrenia. Principal Observations: Seven of the depressed patients reported significant improvement in depressive symptomatology, and seven of the schizophrenic subjects reported amelioration of anxiety and restlessness. Conclusions: These preliminary results suggest that low‐frequency rTMS may be beneficial mainly in MD and to some extent in schizophrenia, and support the need for controlled studies to further validate its therapeutic potential. Depression and Anxiety 7:65–68, 1998.

Motor and somatosensory conduction in cervical myelopathy and radiculopathy.

Study Design. Motor and sensory conduction times were measured in patients with cervical myelopathy and radiculopathy. The results were compared with those of control subjects. Objective. To evaluate the clinical value of the combined use of motor-evoked potentials with F wave recording and somatosensory-evoked potentials in cervical myelopathy and radiculopathy. Summary of Background Data. Electromyography and somatosensory-evoked potentials provide only indirect information on the motor pathways. The development of magnetic transcranial stimulation has provided a direct and reliable physiologic insight into the motor system. Methods. Magnetic stimulation of the motor cortex and nerve roots with F wave recording was used to assess central and peripheral motor conduction times. Somatosensory conduction was evaluated by somatosensory-evoked potentials. Results. Significant prolongation of the central sensory and motor conduction times was found in the group with myelopathy. These findings were much more pronounced in patients who had multiple level spondylotic stenosis of the spinal canal than in those harboring a single disc herniation compressing the spiral cord. In Contrast to somatosensory-evoked potentials, motor-evoked potentials combined with F wave recording showed marked Impairment of peripheral conduction. In patients with radiculopathy. Conclusion. Motor-evoked potentials associated with F wave recording was suitable for the evaluation of patients with radiculopathy, The severity of conduction impairment in patients with myelopathy can be assessed by combined motor-evoked potentials and somatosensory-evoked potentials.

Motor cortex activation by H-coil and figure-8 coil at different depths. Combined motor threshold and electric field distribution study.

OBJECTIVE To compare the ability of an H-coil and figure-8 coil to stimulate different motor cortex regions. METHODS The resting (rMT) and active (aMT) motor thresholds were measured for the right hand APB and leg AHB muscles in 10 subjects, using an H-coil and a figure-8 coil. The electric field distribution induced by the coils was measured in a head model. The combination of the hand and leg MTs with the field measurements was used to determine the depth of hand and leg motor areas via the intersection points. RESULTS The rMT and aMT of both APB and AHB were significantly lower for the H-coil. The ratio and difference between the leg and hand rMT and aMT were significantly lower for the H-Coil. Electric field measurements revealed significantly more favorable depth profile and larger volume of stimulation for the H-coil. The averaged intersection for the APB was at a distance from coil of 1.83±0.54cm and at an intensity of 97.8±21.4V/m, while for the AHB it was at a distance of 2.73±0.44cm and at an intensity of 118.6±21.3V/m. CONCLUSION The results suggest a more efficient activation of deeper motor cortical regions using the H-coil. SIGNIFICANCE The combined evaluation of MTs by H- and figure-8 coils allows measurement of the individual depth of different motor cortex regions. This could be helpful for optimizing stimulation parameters for TMS treatment.

Antidepressant effects of different schedules of repetitive transcranial magnetic stimulation vs. clomipramine in patients with major depression: relationship to changes in cortical excitability

The antidepressant effects of repetitive transcranial magnetic stimulation (rTMS) that have been demonstrated in recent studies could be related to its ability to modulate cortical excitability. Yet, the relationship between stimulus location and frequency and treatment outcome has not been established. The aim of the present study was to compare efficacy of rTMS in various configurations and clomipramine treatment in patients with major depression (MD) and to evaluate the relationship between clinical outcome and changes in cortical excitability. Fifty-nine MD patients were randomized to receive (1) left (n = 12) or right (n = 12) 3 Hz rTMS with placebo medication; (2) left (n = 10) or right (n = 9) 10 Hz rTMS with placebo medication; (3) active medication (clomipramine) with sham rTMS (n = 16). Both 3 Hz and 10 Hz rTMS were administered to the prefrontal cortex by a circular coil at an intensity of 110% and 100% of the resting motor threshold (rMT) respectively. Measurements of cortical excitability were performed prior to and 24 h after completion of 2 wk of daily rTMS or pharmacological treatments. These included the rMT, silent period threshold (SPT), inter-threshold difference (ITD), MEP/M-wave amplitude ratio and silent period duration (SPD). Severity of depression was blindly assessed by the Hamilton Depression Rating Scale (HDRS). The best improvement scores were seen in patients who received left 3 Hz rTMS. The 10 Hz rTMS treatment was less tolerated resulting in a significantly higher dropout rate. A significant increase of the MEP/M wave amplitude ratio accompanied by a shortening of the SPD was evidenced in patients who showed marked clinical improvement (reduction in HDRS by 50% or more) following left rTMS regardless of stimulation frequency. Our results suggest that 3 Hz left rTMS has a higher therapeutic efficacy and tolerability in patients with MD. The enhancement of cortical excitability may be related to the antidepressant action of rTMS.

Effect of electroconvulsive therapy on cortical excitability in patients with major depression: a transcranial magnetic stimulation study

OBJECTIVE The antidepressant action of electro-convulsive therapy (ECT) and repetitive transcranial magnetic stimulation (rTMS) may be related to their ability to modulate cortical excitability. The aim of this study was to investigate changes in cortical excitability following ECT in patients with major depression (MD) and to compare therapeutic efficacy of ECT combined with rTMS to that of ECT alone. METHODS Twenty-two patients with MD were assigned to receive ECT and right prefrontal 1 Hz rTMS (n=12) or ECT with sham rTMS (n=10). ECT was given twice weekly and rTMS was applied on the remaining 4 days, throughout 3 weeks. The resting motor threshold (rMT) and motor evoked potential (MEP)/M-wave area ratio were evaluated before and 6 h after the first, third and sixth ECT session. The active motor threshold (aMT), intra-cortical inhibition (ICI) and intra-cortical facilitation (ICF) were measured at baseline and 24 h after the last ECT. RESULTS There were no significant differences in the degree of clinical improvement and measures of cortical excitability in the ECT+active rTMS group as compared to the ECT+sham rTMS group. Marked clinical improvement observed in 19 out of the 22 patients was associated with a significant increase of the MEP/M-wave area ratio, decrease of the aMT and reduction of the ICI in the left hemisphere. CONCLUSIONS The antidepressant effect of ECT was associated with an enhancement of left hemispheric excitability. rTMS did not add to the beneficial effect of ECT. However, the small sample size and the robust effect of ECT might have obscured a potential therapeutic effect of rTMS. SIGNIFICANCE Measures of cortical excitability may provide insight to our understanding of the mechanism of action of ECT and might be useful for the assessment of treatment response.

Altered excitability of the motor cortex after minor head injury revealed by transcranial magnetic stimulation.

SummaryThis study attempts to find out whether the motor evoked potential (MEP) elicited by single pulse and slow-rate (1 Hz) repetitive transcranial magnetic stimulation (TMS) can disclose concealed subclinical impairments in the cerebral motor system of patients with minor head injury.The motor response to single pulse TMS (STMS) of the patient groups was characterized by significantly higher threshold compared with that of the control group. The central motor conduction time, as well as the peripheral conduction time were normal in all patients pointing to cortical impairment.Two main patterns of MEP changes in response to repetitive TMS (RTMS) were observed in the patient group. A. – progressive decrease of the MEP amplitude throughout the stimulation session to a near complete abolition. B. – irregularity of the amplitude and the waveform of the MEP in a chaotic form. The MEP latency remained stable during the whole stimulation session. The MEP abnormalities recovered gradually over the period of a few months.The higher threshold of the motor response to STMS and the abnormal patterns of the MEP to RTMS seem to reflect transient impairment of cortical excitability or “cortical fatigue” in patients who sustained minor head injures. Further study is needed to evaluated the extent and the pathophysiological mechanisms of the central nervous system fatigue phenomenon following head injury.

Brain-stem trigeminal and auditory evoked potentials in multiple sclerosis: physiological insights

Thirty-six patients with multiple sclerosis were evaluated by means of brain-stem trigeminal and auditory evoked potentials. The brain-stem auditory evoked potentials (BAEPs) were abnormal in 26 patients (72.2%). Brain-stem trigeminal evoked potentials (BTEPs) yielded similar results, showing distorted waveforms and/or prolonged latencies in 25 patients (69.4%). As expected, the MRI proved to be the most efficient single test, revealing plaques in 86.4% of the patients evaluated. However, the diagnostic accuracy of MRI was lower than that provided by the combination of the BTEP and BAEP (88.9%). Moreover, in patients having signs of brain-stem involvement, the BTEP, alone and in combination with the BAEP, proved to be more sensitive than the MRI in revealing brain-stem lesions. Correlation between clinical and BTEP findings could be found only in those patients who presented with signs of trigeminal involvement such as trigeminal neuralgia or dysesthesiae. The analysis of the BTEP waveforms showed two distinct types of abnormality-a peripheral type and a central type-suggesting plaques in distinct locations. Both the BTEP and the BAEP demonstrated a correlation with the clinical course of the disease and the condition of the patient at the time of the evaluation. Relapse of the disease was associated with a marked prolongation of the central conduction time in the BTEP and in the BAEP, suggesting the application of such studies to the monitoring of unstable patients in the evaluation of new therapeutic protocols.

Dissociation of somatosensory and motor evoked potentials in non-comatose patients after head injury.

OBJECTIVES This study was performed to evaluate the clinical value of combined use of somatosensory evoked potentials (SEPs) and motor evoked potentials (MEPs) in patients with different brain lesions after head trauma. METHODS A total of 64 patients with minor and moderate head injury were investigated by means of SEPs recorded over the parietal and frontal areas and MEPs following single-pulse transcranial magnetic stimulation (sTMS) and slow-rate repetitive transcranial magnetic stimulation (rTMS). RESULTS In almost 50% of the patients, a dissociated impairment of somatosensory and motor evoked potentials was found. This dissociation was related to different distribution of SEP and MEP abnormalities in head injury subgroups. The higher threshold to sTMS and increased variability of the MEP amplitude during slow-rate rTMS were the most prominent features in patients with focal brain contusions, suggesting impairment of the cortical excitability. SEP abnormalities, as well as central conduction impairments, were more noticeable in patients with diffuse brain injury. CONCLUSIONS A combined analysis of SEPs and MEPs may improve the assessment of cortical dysfunctions and central conduction abnormalities in non-comatose patients with head injury. A slow-rate rTMS may be considered as a complementary technique to the evaluation of the threshold in assessment of the excitability of the motor cortex in minor and moderate head injury.

Monitoring of brain-stem trigeminal evoked potentials. Clinical applications in posterior fossa surgery

Brain-stem trigeminal evoked potentials (BTEPs) were monitored intraoperatively in 17 patients during posterior fossa surgery. Satisfactory BTEP recording was performed in all patients without technical problems or interfering with the activity of the operating team. The BTEP was not altered by anesthetic agents or muscle relaxants. Intraoperative monitoring of the BTEP showed wave form alterations or increasing peak latencies in 10 patients. Among these patients, the BTEP demonstrated a dynamic correlation with the surgical process in 8 instances. Two major causative surgical manipulations were identified: cerebellar retraction in 4 cases and tumor dissection from the brain-stem in 6 cases. Withholding the dissection of the tumor, readjusting a cerebellar retractor or further modifying the surgical attitude resulted in partial or complete return of the wave form in 7 patients. The BTEP at the end of surgery proved to correlate with the immediate surgical outcome in most instances. We concluded that the intraoperative monitoring of the BTEP was feasible and suggested, despite the small number of patients, a potential value in the survey of brain-stem functions during posterior fossa surgery.

Preliminary assessment of the therapeutic efficacy of continuous theta-burst magnetic stimulation (cTBS) in major depression: A double-blind sham-controlled study

BACKGROUND Theta-burst transcranial magnetic stimulation (TBS) has been shown to induce potent and long lasting effects on cortical excitability. In a previous open study, we demonstrated safety, tolerability and antidepressant properties of continuous TBS (cTBS) in major depression (MD). The present study was aimed to evaluate the therapeutic efficacy of cTBS in depressed patients using a double-blind, sham-controlled design. METHODS Twenty nine patients with MD were randomized to receive either active cTBS to the right dorsolateral prefrontal cortex (n=15) or sham cTBS (n=14) for 10 consecutive work days. After the 10th session, patients who received sham TBS were crossed over to active cTBS which consisted of 10 daily sessions. Patients who received active cTBS continued with the same treatment protocol for additional 10 treatments. Each treatment session consisted of 3600 stimuli at an intensity of 100% of the active motor threshold. Severity of depression was assessed weekly. RESULTS Overall, there was no significant difference in the degree of clinical improvement between active and sham cTBS groups. However, in patients whose medication status remained unchanged before the trial (n=8) and in those who were medication-free (n=3), active cTBS resulted in a significantly greater reduction of Hamilton depression scores as compared to sham cTBS. LIMITATIONS A small sample size, confounding effect of medication and short treatment period. CONCLUSIONS Our results suggest that the antidepressant effect of cTBS is modest, yet it might be beneficial to patients nonresponsive to ongoing pharmacological treatment. A direct comparison between cTBS and conventional rTMS protocols is warranted.