Roberto Callieco

Vestibular evoked myogenic potentials in multiple sclerosis patients

OBJECTIVES Vestibular evoked myogenic potentials (VEMPs) are saccular responses to loud acoustic stimuli and are recordable from the sterno-cleido-mastoid muscle ipsilaterally to the stimulated ear. This study aimed to investigate VEMPs in patients suffering from multiple sclerosis (MS), and to compare these findings with both clinical and instrumental data. METHODS We recorded VEMPs from 70 MS patients, whose clinical data were retrospectively evaluated for the possible occurrence of: past and current (with respect to VEMP recording) brainstem and/or cerebellar symptoms; current brainstem and/or cerebellar signs. Sixty-five patients underwent brainstem auditory evoked potentials (BAEPs) recording; 63 of the same patients underwent saccadic eye movement recording and subjective visual vertical (SVV) evaluation. RESULTS VEMPs were abnormal in 31%, BAEPs in 38% and SVV in 21% of the patients. Saccadic eye movements showed a possible brainstem dysfunction in 44.4% of the patients. There was no correlation between the occurrence of abnormalities and the technical means of detection. The same held true for correlations with clinical data, with the exception of the BAEPs; these proved to be more frequently abnormal in patients presenting at neurological examination with brainstem and/or cerebellar signs that were possibly related to the complaint of dizziness. CONCLUSIONS VEMPs should be considered a useful complementary neurophysiological tool for the evaluation of brainstem dysfunction.

Fatigue in multiple sclerosis: multidimensional assessment and response to symptomatic treatment

Sixty relapsing-remitting multiple sclerosis (MS) patients were selected on the basis of their score on the Fatigue Severity Scale (FSS) and formed two groups: 40 patients (fatigued MS; MSf) scored above the 75th percentile of a previously assessed representative MS sample (100 patients), and 20 age- and sex-matched patients (nonfatigued MS patients; MSnf) scored below the 25th percentile. The patients underwent clinical evaluation (Expanded Disability Status Scale (EDSS)), further assessment of fatigue (Fatigue Impact Scale), scales evaluating depression (Hamilton Depression Rating Scale (HDRS) and Beck’s Depression Inventory (BDI)) and neuropsychological tests. All patients were evaluated for muscle fatigability and central activation by means of a biomechanical test of sustained contraction; they also underwent somatosensory evoked potentials (SSEPs) and transcranial magnetic stimulation (TMS). The patients of the MSf subgroup were then randomized to one of the following two treatments: 4-aminopyridine (4-AP) 24 mg/day and fluoxetine (FLX) 20 mg/day. After a one-week titration this treatment proceeded for 8 weeks. At the end of the treatment, EDSS, fatigue and depression scores were further evaluated. At baseline, fatigue test scores consistently correlated with depression and cognitive test scores, but not with the fatigability test. Fatigue scores decreased in both treatment groups in a similar way. Due to the design of the study, this cannot be disjoined from a placebo effect. The changes of fatigue scores could not be predicted in the FLX group, whereas in the 4-AP group higher basal fatigability test scores were associated with greater reduction in fatigue scores.

Prestimulus spectral EEG patterns and the evoked auditory vertex response.

A vigilance-related index (slow wave index, SWI) representing the relative delta + theta amplitude of the 1 sec prestimulus EEG spectrum has been related to latencies and amplitudes of the auditory cortical evoked response (EP) in 12 volunteers. Stimuli were 70 dB SL tone bursts delivered at 10 sec ISI. Four selective averages were obtained for each subject according to the subdivision of the SWI into quartiles. The subjects were divided into 2 groups having individual mean SWI values above or below the groups median SWI. Repeated measures MANOVA showed that N1 latency increased within subjects from the first to the fourth SWI quartile and that it was longer in subjects with high mean SWIs. N1-P2 amplitude decreased within subjects from the first to the fourth SWI quartile, but only in the group with high mean SWI.

Amodal completion in texture visual evoked potentials

Amodal completion refers to the phenomenological finding of perceiving partly occluded objects as continuing uninterrupted behind an occluder. The outlying problem is how the visual system processes such non-local stimuli because the known processes of early vision are spatially restricted operations which segregate local differences in the visual image, and little is known about their interactions in producing the segmentation of the image into functionally coherent, or global, objects. We recorded human visual evoked potentials (VEPs) to texture stimuli and addressed local/non-local relationships in comparing a condition in which local edges were present, due to texture segregation, with a condition in which, in addition to local edges, textures appeared to continue as surfaces behind gray stripes due to non-local amodal completion. Subtraction of offset from onset responses showed: (1) a difference component due to texture segregation characterized by a negativity with onset at about 95 ms and lasting up to about 280 ms; (2) a further negativity, specifically elicited by amodal completion, with onset at about 142 ms, peaking at 175 ms, and lasting up to about 188 ms. Therefore, amodal completion occurs at an early processing stage of image analysis and the difference component in VEPs can be related to figure-ground perception.

Computed tomography and pattern reversal visual evoked potentials in chronic schizophrenic patients

ABSTRACT— Eighteen chronic schizophrenic subjects treated with a uniform dosage (4–6 mg/day p. o.) of haloperidol were submitted to computed tomography (CT) and to pattern reversal visual evoked potentials (VEPs). Compared to age‐matched controls, schizophrenic patients showed lateral and third ventricular enlargement, greatly delayed VEP latencies and reduced amplitudes. These abnormalities were not related to diagnostic subgroups. Schizophrenic patients with a positive family history for major psychiatric disorders showed normal CT scan measures and greatly abnormal VEP measures, whereas patients with a negative family history showed CT scan signs of atrophy and less pronounced VEP abnormalities.

Usefulness of trigeminal somatosensory evoked potentials to detect subclinical trigeminal impairment in multiple sclerosis patients

Trigeminal somatosensory evoked potentials (TSEPs) by surface electric pulse stimulation were recorded in 30 normal subjects and in 70 multiple sclerosis (MS) patients, 13 of whom presenting clinical trigeminal impairment. We observed significant prolongation of all TSEPs parameters in MS group. TSEPs were abnormal in 45 patients (64.3%). Clinical and neurophysiological data agreed in 36 patients (51%) on 84 sides (60%). TSEPs were able to detect clinically silent lesions 54 times. TSEPs recording proves to be an additional useful test in MS multimodal evoked potential protocols.

Recovery functions of early cortical median nerve SSEP components: normative data.

The recovery functions of parietal P14-N20, N20-P27 and frontal P22-N30 amplitudes were assessed in 17 healthy controls aged 20-50 years by means of the paired stimulus technique. One unpaired and 4 paired stimuli with interstimulus intervals (ISIs) of 25, 50, 75 and 100 msec were cyclically presented in a single run. Responses to the unpaired stimulus were subtracted off-line from paired stimulus responses. The highest suppression was reached at shorter ISIs for components with shorter latencies. The mean suppression of P22-N30 was influenced by the subjects age, being greater in younger subjects. Normative data are reported.

Circadian and hypothermia-induced effects on visual and auditory evoked potentials in multiple sclerosis

OBJECTIVES Body cooling has been proposed as a symptomatic treatment for multiple sclerosis. This study aimed to assess the effects of body cooling and of circadian variations on clinical parameters and on visual and auditory evoked potential measures in multiple sclerosis patients. METHODS Clinical status was assessed and VEPs, BAEPs and MLAEPs (all with two stimulus frequencies) were recorded a total of 4 times on two separate days (two times per day at 08:30 and 15:00 h each day) in 10 multiple sclerosis patients and 10 controls. On one of these days, the subjects were submitted to body cooling before the afternoon session. RESULTS Tympanic temperature was significantly higher in the afternoon. Cooling lowered the temperature by 1.4 degrees C. No clinical effects were observed. Circadian effects were detected on VEP amplitude, which increased both in controls and in patients at low stimulus frequency (P<0.01), and increased in controls and decreased in patients at high stimulus frequency (interaction: P<0.01). Cooling determined an increase in BAEP I-V peak-to-peak time in controls, and a reduction in patients at high stimulus frequency (interaction: P<0.01). In patients, cooling also determined a great increase in MLAEP amplitude (interaction: P<0.001). We did not find cooling effects on VEP measures. CONCLUSIONS Visual and auditory evoked potentials showed differences in circadian and cooling effects between controls and multiple sclerosis patients. These differences are consistent with the hypothesis of temperature-dependent conduction blocks in demyelinated fibers. Cooling may have a clinical effect in selected patients only.

Middle latency auditory evoked potentials improve the detection of abnormalities along auditory pathways in multiple sclerosis patients

Brain-stem and middle latency auditory evoked potentials (BAEPs and MLAEPs) have been studied in 34 multiple sclerosis (MS) patients. We were able to detect a central nervous system auditory pathway involvement in 17 (50%) of the patients: 38% by BAEPs alone (I-V inter-peak latency) and 47% by MLAEPs alone (Na and Pa peak latency). Five patients had abnormal MLAEPs with normal BAEPs whereas the opposite was detectable in only 1 patient. In addition, most MLAEP parameters in the MS group statistically differed from those obtained in the control group. Therefore, our results demonstrated that the auditory pathway impairment could frequently be located at a rostral level along the auditory radiation. In conclusion, even if only Na and Pa components were considered, MLAEPs succeeded in improving the sensitivity of the auditory evoked potential examination without increasing the false positive rate.

Eye movement abnormalities in myotonic dstrophy

We studied saccade and smooth pursuit eye movements in 31 patients suffering from myotonic dystrophy (MD). On the basis of mean value comparisons, saccades were slower and hypometric and smooth pursuit eye movements performed worse in MD patients than in controls. On an individual basis, saccade duration was prolonged in 67.7%, saccades were hypometric in 19.4%, saccade latency was delayed in 9.7%, and the smooth pursuit performance index was decreased in 9.7% of patients. Eye movement abnormalities did not correlate with those detectable by visual, brain-stem auditory and somatosensory evoked potentials. We attempted to classify eye movement abnormalities as myogenic or neurogenic on the basis of differences in combination of eye movement abnormalities and the occurrence of D5/D35 dissociation; the latter consists of a prolonged duration for large (35 degrees) but not for small (5 degrees) saccades. Since D5/D35 dissociation occurred in 26/33 multiple sclerosis patients with increased saccade duration, we considered it to be a neurogenic pattern attributable to a central nervous system (CNS) dysfunction. A prolonged duration without dissociation especially in combination with saccade hypometria, is interpreted as a myogenic pattern, although the lack of dissociation may also occur with CNS impairment in case of a marked increase in saccade duration. Accordingly we classified the oculomotor abnormalities detected as neurogenic in 11 MD patients and as myogenic in another 10, but in some subjects belonging to the second group concomitant CNS impairment is not to be excluded.