The clinical role of somatosensory evoked potential studies: a critical appraisal

Reliability, validity and clinical usability of a robotic assessment of finger proprioception in persons with multiple sclerosis

BACKGROUND

Multiple sclerosis often leads to proprioceptive impairments of the hand. However, it is challenging to objectively assess such deficits using clinical methods, thereby also impeding accurate tracking of disease progression and hence the application of personalized rehabilitation approaches.

OBJECTIVE

We aimed to evaluate test-retest reliability, validity, and clinical usability of a novel robotic assessment of hand proprioceptive impairments in persons with multiple sclerosis (pwMS).

METHODS

The assessment was implemented in an existing one-degree of freedom end-effector robot (ETH MIKE) acting on the index finger metacarpophalangeal joint. It was performed by 45 pwMS and 59 neurologically intact controls. Additionally, clinical assessments of somatosensation, somatosensory evoked potentials and usability scores were collected in a subset of pwMS.

RESULTS

The test-retest reliability of robotic task metrics in pwMS was good (ICC=0.69-0.87). The task could identify individuals with impaired proprioception, as indicated by the significant difference between pwMS and controls, as well as a high impairment classification agreement with a clinical measure of proprioception (85.00-86.67%). Proprioceptive impairments were not correlated with other modalities of somatosensation. The usability of the assessment system was satisfactory (System Usability Scale ≥73.10).

CONCLUSION

The proposed assessment is a promising alternative to commonly used clinical methods and will likely contribute to a better understanding of proprioceptive impairments in pwMS.

Spinal Cord Infarction: A Single Center Experience and the Usefulness of Evoked Potential as an Early Diagnostic Tool

Background: Spinal cord infarction (SCI) is a rare disease and its early diagnosis is challenging. Here, we described the clinical features and imaging findings of SCI, and assessed the results of evoked potential (EP) studies to elucidate their diagnostic role in the early stage of SCI.

Methods: We retrospectively analyzed 14 patients who had spontaneous SCI. The demographic, neurological, and temporal profiles of the SCI patients were identified. We reviewed the imaging findings and assessed the changes in them over time. To review EP, central motor conduction time (CMCT) and somatosensory evoked potential (SEP) values were obtained. We also enrolled 15 patients with transverse myelitis (TM), and compared the clinical, radiological and electrophysiological features between SCI and TM patients.

Results: The ages of the SCI patients ranged from 54 to 73 years. Nine patients (64.3%) showed nadir deficits within 6 h. The most common type of clinical visit was via the emergency center. Nine patients (64.3%) presented with peri-onset focal pain. The median initial modified Rankin scale score was 3. For 9 patients (64.3%), initial T2 imaging findings were negative, but subsequent diffusion weighed imaging (DWI) showed diffusion restriction. Vertebral body infarction was observed in 5 patients (35.7%). EP data were available for 10 SCI patients. All 8 patients who had their CMCT measured showed abnormalities. Among them, motor evoked potentials were not evoked in 6 patients at all. SEP was measured in 10 patients, and 9 of them showed abnormalities; one of them showed no SEP response. For 5 patients, the EP studies were done prior to DWI, and all the patients showed definite abnormalities. The abnormalities in the EP findings of the SCI patients were more profound than those of the TM patients, even though the duration from the onset to the start of the study was much shorter for SCI patients.

Conclusion: SCI can be diagnosed based on typical clinical manifestations and appropriate imaging studies. Our study also indicates that immediate sensory and motor EP study can have an adjuvant diagnostic role in the hyperacute stage of SCI, and can improve the accuracy of diagnosis.

Hypoglycemic sensorimotor polyneuropathy associated with insulinoma

Hypoglycemia-induced peripheral neuropathy due to insulinoma is unusual and, as far as we know, has previously been reported in only 34 patients. In this case report, we describe the clinical features, electrophysiological features, and pathological findings in a 37-year-old patient with polyneuropathy from repeated hypoglycemic episodes over a 9-year period that related to an insulinoma. The literature is discussed. The reported case is of special interest because the peripheral neuropathy led to the correct diagnosis.

Detailed evaluation of evoked potentials in Wilson's disease

Detailed evoked potentials (EPs) were studied in 52 patients (28.7 +/- 11.9 years) with Wilson's disease (WD). Various peak latencies, interpeak latencies and amplitudes of somatosensory, auditory brain-stem and visual EPs were significantly abnormal in the group of 28 neurologically symptomatic patients as compared to controls. Interhemisphere latency and amplitude differences tended to be increased without reaching significance, indicating a symmetrical rather than focal subclinical brain involvement. Selected conduction times of at least 1 EP modality were prolonged in all 4 patients with severe, in 16 of 18 with moderate, in 4 of 6 with mild, and in 4 of 24 patients without neurological symptoms. Auditory brain-stem and somatosensory EPs were more frequently prolonged than visual EPs (more abnormalities with check sizes of 13 than 54 min of arc). Cortical somatosensory EPs correlated well (P much less than 0.01) with either Fz or earlobe reference.

Estimate of motor conduction in human spinal cord: slowed conduction in spinal cord injury

By using motor evoked potential (MEP) created by transcranial electric stimulation over the motor cortex and F-wave measurement from the peripheral nerve stimulation, it is possible to estimate the spinal cord motor conduction velocity (SCMCV) in the diseased state. Twenty-four patients with spinal cord injury (SCI) between T1 and T11 neurological levels participated in this study. MEP in leg muscle was absent in all neurologically complete paraplegics. In 16 patients with neurologically incomplete SCI, MEP was obtained in 13 patients. The SCMCV estimated from C7 to T12 spinal levels was 32.1 (SD = 9.4) m/s. This was significantly slower than 63.3 (SD = 8.6) m/s in 40 normal controls. This noninvasive, indirect method is measurable, and can provide valuable electrophysiological data in the assessment of motor function in patients with SCI.

Evoked potentials and CSF-immunoglobulins in MS: relationship to disease duration, disability, and functional status

In 100 MS patients, BAEP and tibial SEP abnormality rates increased significantly with disease duration and clinical disability. VEP correlated non-linearly with disease duration, and median nerve SEP correlated with disability. In multifactorial analysis, however, BAEP correlated significantly only with clinical brainstem and cerebellar signs. These results suggest that evoked potentials correlate more strongly with neurological status of the functional subsystems than either overall disability or disease duration. These findings indirectly suggest that evoked potentials may be useful monitors during large therapeutical trials in MS patients.

Latency and amplitude abnormalities of the scalp far-field P14 to median nerve stimulation in multiple sclerosis. A SEP study of 122 patients recorded with a non-cephalic reference montage

The frequency and characteristics of P14 abnormalities were investigated in 122 patients with probable (68), or definite (54) multiple sclerosis by recording SEPs to median nerve stimulation with a non-cephalic reference montage. The most frequent SEP abnormality found in our series (62% of abnormal results) combined latency increase and amplitude reduction of P14. Interindividual variability, inherent in absolute amplitude measurements, was by-passed by calculating the ratio between the amplitudes of far-field P9 and P14 components, which proved to be normally distributed in controls. In spite of the strong association (P much less than 0.001) between the P9-P14 interpeak interval (IPL) and the P9/P14 amplitude ratio in MS patients, the latter parameter was found to be the only abnormality in 12 patients whose P9-P14 and P14-N20 IPLs were normal. Also IPLs were increased in 12 patients with normal P14 amplitudes. These results suggest that adding the P9/P14 amplitude criterion to standard IPL data might be useful to detect conduction troubles in MS patients.

The influence of height, age and gender on the interpretation of median nerve SEPs

Median nerve SEPs were studied in 120 normal subjects. Highly significant correlations with height and age were found for all SEP peak latencies, but not for the interpeak latency N19-N13. A significant gender difference was found for N13 and N19 peak latencies, the males having longer latencies. No sex-related correlations in central conduction time could be shown. It is emphasized that reliable SEP interpretation should include simultaneous height, age and gender corrections.

Some comments on the clinical use of evoked potentials

In this survey we describe the uses of somatosensory, visual, and auditory evoked potentials (EPs), adding some critical comments on the values and pitfalls of these methods. It must be stressed that the application of EPs is most valuable when combined with a thorough neurological examination. There is general agreement that EP measurement is one of the best techniques for objective, noninvasive study of brain function in humans.

Validity of median nerve somatosensory evoked potentials in the diagnosis of supraclavicular brachial plexus lesions

Experience with median nerve SEPs in the diagnosis of brachial plexus lesions is analysed in 49 patients selected from a total material of 264 cases with brachial plexus problems tested by SEP techniques. Median nerve SEPs were always compared with the results of SEPs after stimulation of at least one other nerve relevant to the site of the lesion as suspected clinically and electromyographically. All patients presented with unilateral brachial plexus problems and all root lesions were verified by clinical presentation, EMG studies, myelogram or surgery. There were 19 brachial plexus injuries, 13 cases with cervical spondylopathic radiculopaties without myelopathy and 7 patients presented brachial plexopathy with systemic cancer. It was found that median nerve SEPs were always normal in injuries of upper trunk and root avulsions confined to one or two root levels. Median nerve SEPs were abnormal in multiple trunk lesions and multiple root avulsions. In patients with spondylopathic radiculopathies median nerve SEPs were normal apart from one case where involvement of multiple roots was present. Median nerve SEPs were useful in assessing patients presenting brachial plexus problems in the presence of systematic cancer apart from cases where lower trunk involvement was present. In general, median nerve SEPs are useful if they are combined with SEP testing of other nerves anatomically more closely related to the problem as outlined clinically and electromyographically.

A double-blind trial of hyperbaric oxygen in the treatment of multiple sclerosis

A randomized double-blind trial of hyperbaric oxygen (2 atmospheres absolute for 20 sessions of 90 minutes, over a period of one month) demonstrated no advantage over a placebo gas mixture in the treatment of multiple sclerosis. Of 41 patients completing the trial, 21 had been treated with oxygen, eight of whom reported improvement (two confirmed objectively). Of 20 patients in the placebo group, seven claimed improvement (four confirmed objectively). Even when patients with mild disease were considered separately, or when functional systems were assessed individually, no benefit could be shown to result from hyperbaric oxygen therapy.