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Biomedical subjects

C Yiannikas

Publications and source records attributed to C Yiannikas.

At least 37 records · Page 2Linked to original sources
PubMed1991

Regional cerebral blood flow and recognition memory in elderly normals: potential application to Alzheimer's disease.

Regional cerebral blood flow, a physiological measure of brain function, has been used for the assessment of cognitive dysfunction in Alzheimer's disease. A number of studies have found diminished temporo-parietal regional cerebral blood flow (RCBF) in Alzheimer's disease patients at rest and have differentiated these patients from normal subjects with a high degree of sensitivity. However the majority of the Alzheimer's disease patients have been in the moderate to severe stages of the disorder. Few studies have assessed RCBF in the early stages of Alzheimer's disease. With increasing emphasis now being placed on the early detection of such patients we chose to examine RCBF during a task which made demands on those cognitive processes which are impaired in the early stages of the disease, viz. a recognition--memory task. Using a 32-channel RCBF system, we examined 20 normal control subjects over the age of 60 years and 10 patients with early to moderate Alzheimer's disease. RCBF was examined during a task of recognition--memory, and also at rest. Normal subjects showed a global increase in RCBF, with marked left frontal activation, as compared with when at rest. Resting perfusion was decreased in the Alzheimer's subject, and there appeared to be a greater degree of intersubject variability in flow during activation.

Aged↗
PubMed1990

Treatment of idiopathic spasmodic torticollis with botulinum-A toxin: a pilot study of 19 patients.

Nineteen patients with spasmodic torticollis, unresponsive to standard therapy, were administered local injections of botulinum-A toxin into the affected muscles. During an average follow-up period of 11.5 months, a more than 25% improvement was noted in 14 of 19 patients. All those with purely focal dystonia and 9 of 10 patients with a disease history of less than three years benefited from treatment. Side effects were insignificant and transient. Botulinum toxin is a very effective and safe method of treatment for spasmodic torticollis.

Adult↗
PubMed1990

Multimodality evoked potentials in motor neuron disease.

We performed median and tibial nerve somatosensory evoked potentials (SEPs), pattern-shift visual evoked potentials (PSVEPs), and brain-stem auditory evoked potentials (BAEPs) on 27 patients with motor neuron disease (MND). Median and tibial nerve SEPs were abnormal in 8 (30%) of 27 and 3 (14%) of 21 patients tested, respectively. Central and peripheral abnormalities were recorded in the absence of spondylosis. As a group, patients with MND and no evidence of cervical spondylosis had normal conduction to Erb's point following median nerve stimulation, but conduction times beyond this point were prolonged. The PSVEPs and BAEPs were within normal limits in all patients, excluding abnormalities attributable to other disease, but the group P100 latency was significantly prolonged in the group with MND. The BAEPs were normal in the group with MND. This study provides neurophysiological evidence of sensory system involvement in MND.

Brain Stem↗
PubMed1990

Lead intoxication in an anuric patient: management by intraperitoneal EDTA.

Treatment of lead intoxication with intravenous ethylene-diamine-tetra-acetic acid (EDTA) depends on the urinary excretion of chelated lead. This route of excretion was absent in a 48-year-old patient with childhood lead exposure and end stage renal failure who developed encephalopathy and a rapidly progressive neuropathy thought to be due to acute lead intoxication. Diagnosis was confirmed by lead chelation with EDTA and neurophysiological studies. EDTA was added by the patient to her chronic ambulatory peritoneal dialysis (CAPD) fluid each week and chelated lead excreted in the dialysate. Intraperitoneal administration of EDTA was 70% as efficient in removing lead as intravenous administration. Four months of home chelation therapy was associated with resolution of the encephalopathy but no improvement in the peripheral neuropathy.

Anuria↗
PubMed1990

P300 event-related potentials in de novo Parkinson's disease.

Recent studies indicate subtle cognitive deficits in many non-demented Parkinson's disease (PD) patients. Long-latency event-related potentials (LL-ERPs) index the nature and timing of a cognitive response to a stimulus and have been used to assess cognitive function in PD. Studies to date have only assessed patients receiving long-term anti-PD therapy, which may itself affect information processing. In this study we recorded the P300 using a standard auditory oddball paradigm with a button-press response in a group of de novo patients. A P300 was absent in 2 patients and prolonged in 2 patients but there was no difference in the latency or amplitude of the P300 in the Parkinsonian group compared with the age-matched control group. The averaged P300 of the young PD group was dispersed compared with that of the young controls. Our findings suggest that the amplitude and latency of P300 elicited using the paradigm of this study are not sensitive indices for differentiating PD patients from controls. A paradigm which places a greater load on the specific cognitive deficits of PD will be investigated. The dispersion of the P300 component in the young PD group may be support for the suggestion of distinct subgroups in PD. Our findings suggest that the latency and amplitude of LL-ERP components elicited by our paradigm were not sensitive indices for distinguishing PD patients from controls. The significance of the prolonged P3-RT measure is not clear.

Adult↗
PubMed1989

Functional prognosis in stroke: use of somatosensory evoked potentials.

Median nerve somatosensory evoked potentials (SEPs) were performed on 35 patients with acute stroke and correlated with functional outcome as measured by placement, length of stay and an activities of daily living index (Barthel Index). There was a statistically significant correlation of both SEP and sensory examination at the 0.05 level to eventual functional outcome. SEPs were better than age, sex and side of CVA in predicting functional outcome as measured by these scores. SEPs and sensory examination are interrelated but SEPs offer the advantages of objectivity, the ability to quantify results and the use in unconscious or dysphasic patients.

Activities of Daily Living↗
PubMed1988

The origins of lumbosacral spinal evoked potentials in humans using a surface electrode recording technique.

Somatosensory evoked potentials were recorded over the lumbar spine and scalp in 12 normal subjects after stimulating the posterior tibial nerve at the knee and ankle and the sural nerve at the ankle. The H-reflex from the soleus muscle was recorded at the same time. The effects of stimulus intensity, frequency of stimulation and vibration were assessed. It was concluded that when the posterior tibial nerve was stimulated in the popliteal fossa, three negative peaks were recorded over the lumbosacral area. They arose from activity in the dorsal roots, the dorsal horn of the spinal cord (SD) and the ventral roots. In contrast when the posterior tibial nerve and the sural nerve were stimulated at the ankle only two negative peaks were recorded, a dorsal root potential and a spinal cord dorsum potential. In addition the data suggested that the peripheral nerve fibres that are involved with generating the surface recorded spinal potential with mixed nerve stimulation are primarily muscle afferents.

Adult↗
PubMed1988

Peripheral neuropathy associated with mitochondrial myopathy.

Twenty patients with mitochondrial myopathy were investigated for the presence of peripheral neuropathy. There were clinical features of a mild sensorimotor neuropathy in five patients (25%) and nerve conduction studies were abnormal in 10 patients (50%). Electrophysiological studies of the whole group showed significant impairment of motor and sensory conduction compared with controls. Sural nerve biopsy and morphometric studies were performed on four patients with clinical neuropathy. There was a reduction in density of myelinated fibres and electron microscopic features of axonal degeneration affecting myelinated and unmyelinated fibres were in evidence. Abnormal mitochondria containing paracrystalline inclusions were seen in the Schwann cell cytoplasm of two nerves.

Adolescent↗
PubMed1988

Somatosensory evoked potentials, electroencephalography and CT scans in the assessment of the neurological sequelae of decompression sickness.

Decompression sickness can lead to neurological complications. Recovery may be studied by somatosensory evoked potentials (SEPs), which are more sensitive than normal methods of neurological examination, and by electroencephalography (EEG). The combination of EEG and SEP may be useful in differentiating among spinal, brainstem and cortical pathology.

Adult↗
PubMed1987

The relevance of contralateral recordings and patient disability to assessment of brain-stem auditory evoked potential abnormalities in multiple sclerosis.

Brain-stem auditory evoked responses (BAER) were recorded in a group of 83 patients with a diagnosis of clinically definite or probable multiple sclerosis to assess the relevance of recording contralateral responses simultaneously with ipsilateral responses and to correlate patients disability with the detection of abnormalities. The contralateral responses generally mirrored the ipsilateral responses, but in seven patients the responses differed, mainly involving the presence or absence of wave V. However, contralateral recordings did not contribute significantly to the sensitivity of lesion detection, and their main value was to aid in the recognition of waves when they were not clearly seen in the ipsilateral recordings. The BAER abnormality rates were found to be significantly correlated with disability, and it is suggested that this is an important variable to consider when undertaking or comparing results of BAER studies in patients with multiple sclerosis.

Adolescent↗
PubMed1987

Variability on serial testing of pattern reversal visual evoked potential latencies from full-field, half-field and foveal stimulation in control subjects.

The change in pattern reversal visual evoked potential (PRVEP) latency over time (test-retest variability, TRV) was assessed in 30 (16 males, 14 females) adult control subjects using full-field (FF), half-field (HF) and foveal (central-field, CF) stimulation. The mean test-retest interval (TRI) was 20.5 months with a range of 18-21.5 months. There were no significant test-retest latency differences in either sex and furthermore there were no significant inter-sex differences in any of the test-retest parameters. Because of the latter finding the test-retest upper limit of normal for each parameter as defined by the mean value + 2.5 S.D. was taken as the largest value obtained in either sex. Thus the test-retest upper limits of normal for absolute latency from FF, right HF, left HF and CF stimulation were 6, 7, 9 and 7 msec, respectively; for interocular latency differences (ILD) from FF and CF stimulation were 4 and 5 msec respectively; and for right HF to left HF intraocular latency difference (IOLD) was 7 msec. It is concluded that the TRV was sufficiently small in our control group with each of the stimulus techniques to make all of them potentially useful in serial PRVEP studies. Furthermore the extra information provided by CF and HF stimulation may increase the sensitivity and accuracy with which change can be monitored.

Adult↗
PubMed1987

Magnetoencephalography: locating the source of P300 via magnetic field recording.

A description is given of the theory and instrumentation involved in measuring magnetic fields of the brain. The magnetic counterpart of event-related potentials are capable of locating more accurately the generators of these electrical signals. Preliminary results of the first application of magnetoencephalography in Australia are presented. These localize the generator of the auditory P300 event-related potential component to the temporal cortex.

Adult↗
PubMed1986

Short-latency somatosensory-evoked potentials from radial, median, ulnar, and peroneal nerve stimulation in the assessment of cervical spondylosis. Comparison with conventional electromyography.

A study of data on 30 patients with cervical spondylosis was carried out to determine whether short-latency somatosensory-evoked responses (SEPs) to median, ulnar, radial, and peroneal nerve stimulation provided additional information to that obtained by electromyography (EMG), late responses, and peripheral conduction studies. Peripheral studies, EMG results and SEPs were within normal limits in ten patients with pain, but without objective neurological deficit. By contrast, of ten patients who had objective signs of root compression, conventional EMG results were normal in nine, but abnormalities of the SEPs from radial nerve stimulation were obtained in only five patients, and were normal from ulnar and median nerve stimulation. In ten patients with clinical features of myelopathy, seven had abnormal median SEPs and all had abnormal peroneal SEPs, whereas EMG results were abnormal in only five patients. It is suggested that SEPs and EMG are both of limited use in patients with only symptoms of root compression. In patients with signs of root compression, EMG is the most sensitive procedure; however, some additional information can be obtained from superficial radial SEPs. In patients with cervical myelopathy, SEP was the most useful procedure, especially when upper and lower limbs were studied.

Adult↗
PubMed1986

Peripheral neuropathy associated with mitochondrial myopathy.

Twenty patients with mitochondrial myopathy were investigated for the presence of peripheral neuropathy. There were clinical features of a mild sensorimotor neuropathy in 5 patients (25%) and nerve conduction studies were abnormal in 10 patients (50%). Electrophysiological studies of the whole group showed significant impairment of motor and sensory conduction, compared with controls. Sural nerve biopsy and morphometric studies were performed on 4 patients with clinical neuropathy. There was a reduction in density of myelinated fibers and electron microscope features of axonal degeneration affecting myelinated and unmyelinated fibers. Abnormal mitochondria containing paracrystalline inclusions were seen in the Schwann cell cytoplasm of two nerves.

Adolescent↗
PubMed1986

Contribution of pattern reversal foveal and half-field stimulation to analysis of VEP abnormalities in multiple sclerosis.

Multichannel pattern reversal visual evoked potentials (PRVEPs) from full-field (FF), half-field (HF) and foveal (central-field, CF) stimulation were recorded in 112 mildly disabled multiple sclerosis (MS) patients with the aim of evaluating the contribution of HF and CF stimulation in this disease. CF stimulation was marginally more sensitive in detecting abnormalities (75% of patients) than FF stimulation (71% of patients). However, more importantly the two techniques were found to be complementary with the maximum number of abnormalities (79% of patients) resulting from a combination of the results. Abnormal FF responses were further evaluated by HF responses. P100 latency prolongation indicative of conduction delay was the most common finding but one-third of abnormalities consisted of disturbances of wave form relating to conduction block predominantly in macular fibres. Furthermore 34% of patients had an absent or indeterminate response to CF stimulation thus providing electrophysiological confirmation of the preferential involvement of macular fibres in MS. Although electrophysiological abnormalities were localised to the optic nerve in the majority of cases, some patients also had evidence of retrochiasmatic and chiasmatic lesions. In the majority of cases CF stimulation proved to be a useful alternative to HF stimulation in evaluating FF responses with abnormal wave forms. The study also suggested that an important factor determining whether a central scotoma will disturb the morphology of the FF VEP in the midline recording channel is the position of the macular representation in the occipital cortex. It is concluded that with multichannel recording and the additional use of CF and HF stimulation it is possible to increase the yield of PRVEP abnormalities found in MS and to define their nature with considerably greater precision.

Adult↗
PubMed1986

A comparison of brainstem auditory evoked responses evoked by rarefaction and condensation stimulation in control subjects and in patients with Wernicke-Korsakoff syndrome and multiple sclerosis.

Brainstem auditory evoked responses (BAER) evoked by rarefaction and condensation stimulation were compared in patients with Wernicke-Korsakoff syndrome (WKS) and multiple sclerosis (MS) and click polarity-related differences in topodiagnosis were found in 24% of the WKS and 40% of the MS patients. These results suggest the need to record BAER routinely with both stimulus polarities separately if practicable. BAER from rarefaction and condensation stimulation were recorded from control subjects of both sexes to provide control data for the patient study and also to investigate the interaction between sex and click polarity. BAER latency and amplitude differences between males and females were found to be independent of click polarity. However, the study did show an interaction between female sex and click polarity-related BAER latency differences although differences in amplitude and waveform morphology were essentially independent of sex. This further emphasises the importance of taking into account the variables of sex and stimulus polarity in establishing BAER control values.

Adolescent↗
PubMed1984

Abnormalities of proximal conduction in acute idiopathic polyneuritis: comparison of short latency evoked potentials and F-waves.

Motor and sensory conduction studies, F-wave latency, and the latency of evoked potentials from the brachial plexus and cervical spine in response to median nerve stimulation were examined in 17 patients with acute idiopathic polyneuropathy. Short latency evoked potentials provided a higher yield of evidence of abnormalities of proximal conduction than did the F-wave latency. Both methods of studying conduction in the proximal segments of a peripheral nerve may be normal, however, in a small number of patients who have significant pathological lesions.

Adolescent↗