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Biomedical subjects

G T Plant

Publications and source records attributed to G T Plant.

At least 91 records · Page 5Linked to original sources
PubMed1997

An epidemic of optic neuropathy in Tanzania: characterization of the visual disorder and associated peripheral neuropathy.

An epidemic of subacute bilateral visual failure has affected large numbers of teenagers and young adult Africans in coastal Tanzania since 1988. Previous work had indicated that many patients had sensory symptoms, but the nature of the neurological involvement was uncertain. The primary objective of this study was to characterize the accompanying neurological disorder. Furthermore, the nature of the visual loss was uncertain from previous reports as both retinopathy and optic neuropathy had been suggested. Full ophthalmic and neurological examinations were carried out at the Muhimbili University Hospital in Dar es Salaam. Nerve conduction studies, pattern electro-retinograms and cortical visually evoked responses and colour contrast sensitivity tests were carried out. Thirty eight young Africans and 12 controls were included in the study. The characteristic fundus picture was symmetrical temporal optic atrophy, and thinning of the caeco-central nerve fibre layer. Fluorescein angiography was normal. The electrophysiological and colour contrast sensitivity tests confirmed optic neuropathy in the majority of cases but primary retinal involvement was indicated in some. Neurological examination and nerve conduction measurements showed evidence of a peripheral neuropathy in 47% of the patients. The peripheral neuropathy is likely to have involved large fibres (from the nerve conduction studies) but the symptoms suggest small fibre loss also. 42% had developed hearing loss. Urinary thiocyanate levels were uniformly low. Serum was negative for antibodies to HTLV-1. DNA analysis from three cases was negative for three known mutations associated with Leber's hereditary optic atrophy (11778, 3460 and 14484). This entity, occurring predominantly in a young age group, does not correspond closely to other tropical neurological syndromes previously described from East Africa although it is clinically very similar to Strachan's syndrome (originally described in the Caribbean and more recently in prisoners of war) and also to an epidemic of optic and peripheral neuropathy that has recently occurred in Cuba. The aetiology has not yet been determined. A micronutrient deficiency is likely but has not been established.

Adolescent↗
PubMed1997

Intracranial hypertension and HIV associated meningoradiculitis.

Two patients with meningoradiculitis associated with HIV presented with symptoms and signs of intracranial hypertension. In the patients described, the raised intracranial pressure resolved after lumbar puncture. After exclusion of opportunistic infection, such patients may be managed with therapeutic lumbar puncture alone.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Nemaline myopathy: an unusual cause of ophthalmoparesis.

Ophthalmoparesis and ptosis are extremely rare in nemaline myopathy. A 45-year-old man with a long history of bilateral ptosis and a 1-year history of diplopia is reported. Leg and arm weakness and wasting had been present since childhood, with a very slow deterioration over time. On examination, there was nonfatigueable bilateral ptosis that was more marked on the right. There was diplopia on left gaze. Extraocular movements showed limitation of elevation and adduction of the right eye. There was bilateral facial weakness, as well as proximal and distal wasting and weakness in the arms and legs. Electromyography (EMG) showed a combination of myopathic and neurogenic changes. Triceps muscle biopsy showed small multiple collections of rod-like structures in > 50% of fibers. This patient presented with a clinical picture that did not primarily suggest nemaline myopathy. This case illustrates the heterogeneity of this disorder and the need for muscle biopsy to make an accurate diagnosis in patients with ptosis and progressive external ophthalmoparesis.

Biopsy↗
PubMed1996

C-terminal fragments of alpha- and beta-tubulin form amyloid fibrils in vitro and associate with amyloid deposits of familial cerebral amyloid angiopathy, British type.

Familial amyloidosis, British type, is an autosomal dominant disease characterized by progressive dementia, spastic paralysis and ataxia. The identity of the accumulating amyloid is not known, thus preventing the definitive classification of the disease. Biochemical methods were used to characterize the nature of the amyloid deposits from the brain tissue of one individual who died with this disease. The purified tissue material was subjected to trypsin digestion and subsequent N-terminal sequence analysis. Major tryptic fragments yielded the sequences VGINYQPPTVVPGGDLAK, FDLMYAK, GLTVPEL and GYLTVAAVFR, which are all tryptic fragments of the C-termini of human tubulin subunits alpha and beta. Synthetic peptides based on the sequences of these fragments formed amyloid fibrils in vitro fitting the characteristic definition of amyloid. These findings suggest that the C-terminal fragments of both alpha- and beta-tubulin are closely associated to the amyloid deposits of familial amyloidosis, British type.

Amino Acid Sequence↗
PubMed1996

Ocular neuromyotonia.

AIMS/BACKGROUND: Ocular neuromyotonia is characterised by spontaneous spasm of extraocular muscles and has been described in only 14 patients. Three further cases, two with unique features, are described, and the underlying mechanism reviewed in the light of recent experimental evidence implicating extracellular potassium concentration in causing spontaneous firing in normal and demyelinated axons. METHODS: Two patients had third nerve neuromyotonia, one due to compression by an internal carotid artery aneurysm, which has not been reported previously, while the other followed irradiation of a pituitary tumour, a common association in the published reports. Selective activation occurred in both, where neuromyotonic activity was triggered by prolonged voluntary activation of specific extraocular muscles with or without spread of activity to other third nerve muscles. The other patient had fourth nerve involvement, where spasms of the superior oblique muscle were induced only by alcohol, a phenomenon which has not been described. RESULTS: The two patients with third nerve involvement responded to carbamazepine and in one, an improvement in a chronic partial third nerve paresis occurred. The other has not required treatment and remains asymptomatic by refraining from alcohol. CONCLUSIONS: A careful examination, including the effects of prolonged voluntary muscle action is required to initiate episodes and to demonstrate selective activation. Imaging is mandatory to exclude compressive intracranial lesions, particularly where there is no history of pituitary fossa irradiation. A trial of anticonvulsants should be considered in all patients. Extracellular potassium may play a role in spontaneous firing and ephatic transmission in ocular neuromyotonia.

Adult↗
PubMed1995

An epidemic of optic neuropathy and painful sensory neuropathy in Cuba: clinical aspects.

An epidemic of bilateral optic neuropathy and painful sensory neuropathy occurred in Cuba in 1991-1993. Over 45,000 individuals were stated to have been affected. We report a clinical study on 25 patients seen in Cuba in 1993-1994. Affected patients showed either bilateral optic neuropathy with caecocentral scotomata or a distal predominantly sensory neuropathy sometimes associated with deafness, or a combination of both optic and peripheral sensory neuropathy. The nature of the epidemic is discussed. The clinical features in patients with confirmed neurological deficits were consistent with a diagnosis of Strachan's syndrome, probably related to nutritional deficiency. Other patients with similar symptoms showed no evidence either of optic or peripheral neuropathy and were considered to represent disease mimicry on a psychoneurotic basis.

Adult↗
PubMed1995

Recent advances in the electrophysiology of visual disorders.

There have been a number of technical developments in the field of visual electrodiagnosis in recent years, some of which are beginning to "bear fruit" in terms of improving accuracy of diagnosis. In addition there is more information available from electrophysiology and neurochemistry of retinal function that will lead to a clearer understanding of the physiological basis of clinical tests.

Electroretinography↗
PubMed1994

Insights into the different exploits of colour in the visual cortex.

A new method that allows controlled masking of luminance contrast has been developed to study the use of chromatic signals in human vision. The method also makes it possible to examine the different uses of chromatic signals (e.g. the generation of perceived colour, or the construction and representation of object structure and form). By using this technique, we studied the threshold detection of chromatic signals in normal trichromats. The results show that chromatic signals are virtually unaffected by ongoing, randomly varying, luminance contrast changes. These findings suggest that chromatic signals are either processed independently or can be separated completely from any confounding luminance contrast components in the stimulus. Thresholds for detection of colour changes only, and for extraction of stimulus structure from chromatic signals in normal trichromats, in subjects with single cone receptor deficiency (i.e. dichromats) and in three subjects with abnormal colour vision caused by bilateral damage to ventromedial, extra-striate visual cortex (i.e. subjects with cerebral achromatopsia) have also been measured. No significant difference in thresholds for the two conditions was observed either in normal trichromats or in dichromats. Subjects with cerebral achromatopsia, however, reveal markedly different thresholds. The results suggest that chromatic signals are processed independently to generate perceived object colour or to construct spatially structured objects, and that these functions involve different neural substrates. The results help to explain, at least in part, why cerebral achromatopsia is a heterogeneous disorder, and why there can be significant differences in the effective use of chromatic signals in subjects described as cerebral achromatopsics.

Color Perception↗
PubMed1993

Impaired visual motion perception in the contralateral hemifield following unilateral posterior cerebral lesions in humans.

Contrast thresholds for a number of tasks were measured in the contralateral and ipsilateral upper quadrants of the visual field (eccentricity = 10 degrees) before and after an occipito-parietal surgical resection, in one patient, carried out for intractable epilepsy. Postoperatively the contrast thresholds for discriminating the speed of movement of drifting sine-wave gratings were elevated by greater than a log unit in the contralateral field with little or no change in the detection thresholds for the same stimuli. Contrast thresholds for opposite direction-of-motion (DOM) discrimination of a contrast modulated (CMod) grating (a 'non-Fourier' motion stimulus) were also elevated by about a log unit in the contralateral hemifield but thresholds for DOM discrimination of a sine-wave (luminance modulated, LMod) grating were unaffected. Contrast thresholds for orientation discrimination of stationary gratings (a non-motion task) were unaffected. This general pattern of results was found in two other patients following lateral occipital surgical resections. Eight other patients with occipito-temporal (two cases), parietal (three cases) and medial occipital lobe lesions (three cases) showed no difference between the two hemifields on any of the tasks. Comparison of the location of the lesions leads to the conclusion that damage to the lateral occipital gyri is responsible for the pattern of visual deficit observed. Damage to an extra-striate visual area concerned with motion perception (the human homologue of primate V5-MT) may have occurred. There has been no previous description of impairment of motion perception localized to a hemifield in humans. The characteristics of the residual motion perception in these cases is described further in the accompanying article [Plant and Nakayama (1993), Brain, 116, 1337-1353].

Adult↗
PubMed1993

The characteristics of residual motion perception in the hemifield contralateral to lateral occipital lesions in humans.

Unilateral damage to the lateral occipital region in humans can give rise to impaired motion perception in the contralateral visual field [Plant et al. (1993), Brain, 116, 1303-1335]. We report the following characteristics of the residual vision. (i) Spatial acuity and spatial frequency discrimination are not affected. (ii) Contrast thresholds for direction-of-motion (DOM) discrimination of luminance modulated (LMod) sine-wave gratings is unaffected regardless of drift temporal frequency and the effect of spatial and temporal frequency on drifting/counterphase sensitivity ratios is normal (providing further evidence that cortical directionally selective mechanisms are intact). (iii) Contrast thresholds for DOM discrimination of contrast modulated (CMod) gratings are elevated by a log unit across a range of drift velocities. (iv) The residual motion perception shows neither a directional nor a naso-temporal asymmetry. (v) Weber fractions for velocity discrimination are shown in one patient in whom this measurement was carried out, to be elevated by around a factor of three but the functions relating velocity discrimination to stimulus contrast and to the velocity of the standard are parallel in the affected and unaffected hemifields. (vi) Weber fractions for temporal frequency discrimination using counterphase modulated gratings are also elevated. We conclude that the degraded motion perception is mediated by mechanisms which have similar contrast and temporal properties to those subserving normal motion perception. Mechanisms subserving DOM discrimination of LMod gratings may be spared because they are more widely distributed in extra-striate cortex than mechanisms subserving non-Fourier (second-order) motion perception or velocity discrimination. The anomaly resembles that described in some recent animal studies of impaired motion perception after extra-striate cortical damage.

Adult↗
PubMed1993

Frequency and characteristics of visual field deficits after surgery for mesial temporal sclerosis.

In a series of 33 patients undergoing tailored temporal lobe resection for mesial temporal sclerosis, the frequency of postoperative visual field deficit (VFD) was 52%. The size and configuration were similar after operation in the right and left hemispheres. We observed partial upper quadrantanopias in 16 of 28 patients who became seizure-free and in only one of five patients with residual seizures. VFDs may provide an independent measure of the functional extent of resection.

Adult↗
PubMed1992

Symptomatic retrochiasmal lesions in multiple sclerosis: clinical features, visual evoked potentials, and magnetic resonance imaging.

We have studied 18 patients with relapsing-remitting multiple sclerosis (MS) who had symptomatic visual field defects due to retrochiasmal lesions. In 17, the lesion responsible was identified by magnetic resonance imaging (MRI), computed x-ray tomography (CT), or both. The lesion responsible involved the posterior optic radiations in eight cases, the optic tract and lateral geniculate nucleus in six, and the posterior limb of the internal capsule in three. The prognosis for recovery of the field defect was good; complete recovery occurred in 14 patients, and only two showed no recovery at all. The striking characteristic of the lesions was that most were unusually large; indeed, many were detectable on CT as well as MRI. Half-field asymmetries of either amplitude or latency of the visual evoked potentials (VEPs), consistent with a postchiasmal lesion, were present in only five out of 13 patients acutely. In only three of these did the abnormality persist at follow-up. We conclude that only large postchiasmal lesions are likely to cause symptomatic homonymous field defects in MS, usually characterized by rapid recovery. Hemifield VEPs have a low sensitivity for the detection of postchiasmal as compared with prechiasmal abnormalities.

Adult↗
PubMed1991

Partial, non-thrombotic, superior sagittal sinus occlusion due to occipital skull tumours.

Two cases are described in which raised intracranial pressure occurred as a result of superior sagittal sinus (SSS) occlusion by an occipital skull tumour. One was a plasmacytoma, the other a metastatic deposit from a Ewing's sarcoma. The difficulties in diagnosis of this syndrome are illustrated together with the importance and success of appropriate treatment. From the literature it appears possible that these two tumours may be particularly likely to occlude the SSS and the reasons for this are discussed.

Adult↗
PubMed1990

Familial cerebral amyloid angiopathy with nonneuritic amyloid plaque formation.

Two families have been described previously with the features of an autosomal dominant familial cerebral amyloid angiopathy with nonneuritic plaque formation. The clinical features of the cases were dementia, spastic paralysis and ataxia. It has now been established that both families were descended from a common ancestor and the case histories of 26 affected individuals in 5 generations of this pedigree are reported. An autopsy study has been performed on a recent case. The findings are described and compared with the four previously published autopsy studies in this family, which is then discussed in the context of recent advances in the nosology of familial disorders in which cerebral amyloid angiopathy and other forms of cerebral amyloid deposition occur.

Amyloidosis↗