Serial recordings of multimodality evoked potentials in multiple sclerosis: a four year follow-up study

The use of transcranial magnetic stimulation in diagnosis, prognostication and treatment evaluation in multiple sclerosis

Despite advances in brain imaging which have revolutionised the diagnosis and monitoring of patients with Multiple Sclerosis (MS), current imaging techniques have limitations, including poor correlation with clinical disability and prognosis. There is growing evidence that electrophysiological techniques may provide complementary functional information which can aid in diagnosis, prognostication and perhaps even monitoring of treatment response in patients with MS. Transcranial magnetic stimulation (TMS) is an underutilised technique with potential to assist diagnosis, predict prognosis and provide an objective surrogate marker of clinical progress and treatment response. This review explores the existing body of evidence relating to the use of TMS in patients with MS, outlines the practical aspects and scope of TMS testing and reviews the current evidence relating to the use of TMS in diagnosis, disease classification, prognostication and response to symptomatic and disease-modifying therapies.

Pattern reversal visual evoked potentials as a measure of visual pathway pathology in multiple sclerosis

BACKGROUND

Pattern reversal visual evoked potentials (PRVEPs) have a well-documented role in diagnosis of multiple sclerosis (MS), but their value as a visual function surrogate remains controversial.

METHODS

We evaluated PRVEP in 37 patients with MS who were participating in a long-term follow-up study following a phase III trial of interferon beta-1a (Avonex). Patients were examined to determine the Kurtzke Extended Disability Status Score (EDSS), multiple sclerosis functional composite (MSFC), contrast letter acuity (CLA), and had cranial MRI scans to determine whole brain atrophy (BPF). PRVEP was evaluated for P100 latency, amplitude, and waveform morphology. Two summary scores were created: for Score A, abnormal latencies, morphologies, and amplitudes of each individual eye were added; for Score B, abnormal latencies, morphologies, and amplitude ratio between eyes was determined. Sixteen patients in this group also had PRVEP at the time they enrolled in the clinical trial, eight years previously.

RESULTS

At the follow-up exam, over 75% of patients had abnormal PVEP parameters while visual acuity (VA) was abnormal only in 59%. Increased PRVEP latency over the eight-year period correlated with deterioration assessed by EDSS (P = 0.006), BPF (P = 0.0001), and MSFC (P = 0.0041). Score A was significantly correlated with EDSS, BPF, CLA, cognitive function, and quality of life assessed with the Sickness Impact profile. No correlation was seen with the MSFC.

CONCLUSIONS

The results indicate that PRVEP measures MS-related pathology, and can provide not only diagnostic but also prognostic information during evaluation of MS patients.

Serial evoked potential studies and MRI imaging in chronic progressive multiple sclerosis

Measurements of serial evoked potential latencies and plaque burden on MRI scans are often obtained during clinical studies of multiple sclerosis patients to provide additional information to the disability-based primary endpoints. The ideal laboratory-based marker of progression would be expected to significantly change over the time period of study. Serial visual (VEP) and brainstem auditory evoked potentials (BAEP) and MRI scans of 11 chronic progressive MS patients were obtained over a 1.5 year period in a clinical study. Over this period, there was no significant change in disability as measured by the Kurtzke EDSS, Ambulation Index or Neurological Rating Score. The VEP P100 significantly progressed over the period of study. However, the MRI T(2) plaque burden and BAEP I-V intrapeak latency did not significantly progress over the 1.5 years. We conclude that, in chronic progressive MS, serial visual evoked potential tests may complement standard disability-based endpoints to assess disease progression.

Measuring evoked responses in multiple sclerosis

Evoked potentials (EPs) have been widely utilised in Multiple Sclerosis (MS) patients to demonstrate the involvement of sensory and motor pathways. Their diagnostic value is based on the ability to reveal clinically silent lesions and to objectivate the central nervous system damage in patients who complain frequently of vague and indefinite disturbances which frequently occurs in the early phases of the disease. The advent of magnetic resonance imaging (MRI) techniques has greatly reduced the clinical utilisation of EPs, which is not fully justifiable, as the information provided by EPs are quite different from those provided by MRI. The abnormalities of evoked responses reflect the global damage of the evoked nervous pathway and are significantly correlated with the clinical findings, while the vast majority of MRI lesions are not associated to symptoms and signs. Transversal and longitudinal studies have demonstrated that EP changes in MS are more strictly related to disability than MRI lesion burden. On the contrary, MRI is more sensitive than EPs in revealing the disease activity. Evoked responses modifications observed in MS are not disease-specific; moreover longitudinal studies showed latency and morphology changes of evoked responses not always related to clinical changes. Such a dissociation can be explained both by technical factors and by subclinical disease activity. To reduce the negative impact of technical aspects, only reproducible parameters of the evoked responses should be used to monitor disease evolution and therapeutic interventions.

Evoked potential abnormality scores are a useful measure of disease burden in relapsing-remitting multiple sclerosis

Fifty patients with relapsing-remitting multiple sclerosis were examined and studied with serial evoked potential and magnetic resonance imaging (MRI) measurements as part of a clinical trial. An evoked potential abnormality score (EPAS) for each testing session was calculated consisting of the total number of abnormal tests. The EPAS correlated well with Expanded Disability Status Scale (EDSS) at years 0, 1, and 2, with Spearman correlation coefficient scores of 0.68, 0.66, and 0.72, respectively. MRI lesion volume correlations ranged from 0.27 to 0.34 for the EDSS. EPAS are a potentially useful surrogate measure of clinical disability in relapsing-remitting multiple sclerosis.

Neurophysiological and cognitive markers of disease evolution in multiple sclerosis

Both evoked potentials and cognitive tests may provide useful information which cannot be derived from the clinical observation. For this reason, there have been some attempts to use EPs in monitoring the natural history of the disease and in assessing the efficacy of therapeutic trials. However, no conclusion can be derived from the few available data. Although MRI is more sensitive than EPs in revealing new lesions in brain, cerebellum and brainstem, EPs are more sensitive in revealing optic nerve and spinal cord lesions. Moreover, the poor relationship between brain MRI abnormalities and disability has raised the possibility that cognitive evaluation may be an additional sensitive marker of brain involvement over time. Since the gold standard for the assessment of disease activity is uncertain, it is therefore advisable that frequent MRI, EPs and cognitive assessment may integrate clinical outcomes measured by conventional scales, both in the study of the natural disease course and in monitoring clinical trials.

Evoked potentials in clinical trials for multiple sclerosis

Multiple sclerosis produces disruption of conduction in the central nervous system by a variety of mechanisms, relating, in part, to loss of the myelin sheath. Although often not well correlated with the clinical course of the disease in individual patients, the resulting evoked potential (EP) disturbances can serve as measures of an accumulating disease burden, particularly in longitudinal population studies. Accordingly, EPs can serve as useful instruments for assessing the effectiveness of therapeutic agents which may alter the course of the multiple sclerosis. Furthermore, since EPs measure conduction within the central nervous system, they provide a means of directly assessing symptomatic treatments designed to improve central conduction.

Serial evoked potentials in multiple sclerosis bouts. Relation to steroid treatment

Serial recordings of multimodal sensory (visual, acoustic and somatosensory) evoked potentials were made in 19 relapsing-remitting Multiple Sclerosis patients enrolled in a clinical trial designed to evaluate the efficacy of dexamethasone versus high- and low-dose methylprednisolone in acute multiple sclerosis bouts. Electrophysiological and clinical evaluations were performed at the onset of therapy and until 6 months after the end of treatment. Using an arbitrary Evoked Potentials score that takes into account both latency and waveform alterations, we found a positive correlation between evoked potentials and clinical disability scores. Furthermore, different electrophysiological profiles were detected in the three therapeutic subgroups. Evoked potentials may be useful for monitoring acute Multiple Sclerosis bouts and evaluating the effect of therapy.

Correlation of clinical features and findings on cranial magnetic resonance imaging with urinary myelin basic protein-like material in patients with multiple sclerosis

Immunoreactive material that appears to be a peptide encompassing all or a portion of residues 80 to 89 of myelin basic protein is present in normal unconcentrated urine and is increased in certain patients with multiple sclerosis (MS). Compared with normal controls, urines collected randomly from 158 MS patients or in a clinical research unit from 8 patients with MS had higher mean values of urinary MBP-like material (MBPLM). The level of MBPLM in urine showed no direct relationship to MBPLM in cerebrospinal fluid and did not correlate with clinical relapses of disease. In the other neurological disease control group (26 patients), some patients with other inflammatory diseases, but not stroke or early phase Guillain-Barré syndrome, also showed elevations. Among the subtypes of MS, those with secondary chronic progressive disease had the highest values. Urinary MBPLM showed no definite correlation with or effect of treatment with glucocorticoids and immunosuppressants except that a lower level of urinary MBPLM showed a weak relationship with improvement following treatment with methylprednisolone/prednisone. In a serial study of 8 patients with unenhanced cranial magnetic resonance imaging and 20 patients with gadolinium-enhanced cranial magnetic resonance imaging, urinary MBPLM did not show a direct correlation with new or enhancing lesions. Urinary MBPLM does not parallel acute myelin damage but appears to reflect an ongoing process, possibly linked to attempted efforts at remyelination.

Multimodal sensory and motor evoked potentials in a two-year follow-up study of MS patients with relapsing course

Serial recording of multimodal sensory (pattern reversal visual, brainstem auditory, median and tibial somatosensory) and motor evoked potentials during a 2-year period was performed on a group of 25 patients with relapsing multiple sclerosis. A new, 10-degree evoked potentials abnormality scale was introduced. In contrast to the insignificant common trend of both the mean individual EP latency parameters and the mean expanded disability status scale and evoked potentials abnormality scale to deteriorate the changes in both expanded disability status scale (p less than 0.05) and evoked potentials abnormality scale (p less than 0.01) were significant using a 1-point criterion for change and non-parametric testing. Changes in both scales differed in about 50% of patients; contrary to bidirectional changes in the clinical scale, no improvement in the evoked potential scale was found. The introduction of an evoked potentials abnormality scale based on separate cut-off step-like criteria may increase the robustness of evoked potential changes due to the activity of the disease in longitudinal studies.

Improvement in motor evoked potentials and clinical course post-steroid therapy in multiple sclerosis

Motor evoked potentials (MEP) were recorded in 23 patients with definite relapsing multiple sclerosis before and after treatment with a short course of high dose of methylprednisolone. MEP were performed together with clinical examination just before treatment, and 6 and 60 days later. The following results were observed: (1) a statistically significant relationship between the corticospinal deficit and the alteration in MEP, (2) a significant improvement in latency of MEP by day 6, (3) a significant correlation between the change in the Kurtzke disability scale rating and the improvement in MEP. The results provide further evidence for the possible effectiveness of short courses of high dose corticosteroids in the treatment of relapses of multiple sclerosis and the usefulness of MEP in its assessment.

A comparison of clinical and evoked potential (VEP and median nerve SEP) evolution in patients with MS and potentially related conditions

A clinical and electrophysiological (VEP and median nerve SEP) follow-up was performed in 27 subjects selected among 200 consecutive patients previously examined by multimodality evoked potentials because of MS or potentially related conditions. The mean interval between the examinations was 20 months. There was a concordance between the clinical and electrophysiological evolution for the majority of examined pathways. However, alterations were more frequent for evoked potentials than for clinical symptomatology: six VEPs and 16 SEPs were changed compared to the initial recordings whereas clinical alterations occurred in one eye and 11 arms. Definitely contradictory evolutions were observed in only two arms (in one of the MS patients). Significant deteriorations between examinations occurred for two VEPs and two SEPs, although the recordings remained within normal limits. We conclude that evoked potential recordings are valuable for monitoring and that serial recordings may increase the number of abnormal findings.

Interweaving and overlapping of evoked potentials

The refractory effect of one stimulus upon the response to a closely following stimulus in a different modality is much less than upon the response to a stimulus in the same modality. It is therefore far more efficient to record responses to stimuli in different modalities concurrently than to record each one separately. We evaluated 2 techniques for concurrent recording. Interweaving involves recording the response to one stimulus in the intervals between recording responses to other stimuli. Overlapping occurs when two or more responses are at times being simultaneously recorded. Interweaving and overlapping reduced the time required to record auditory brain-stem responses, short-latency somatosensory evoked potentials and pattern-reversal visual evoked potentials by a factor of 3 over the time required to record each response separately. Overlapping caused no significant change in the evoked potentials. Depending upon the actual timing schedule, interweaving may distort the evoked potentials if later parts of the response to one stimulus override the evoked potential to a following stimulus. Filtering and randomization of stimulus timing may attenuate the effects of these overriding potentials.