Reduced occipital GABA in Parkinson disease with visual hallucinations
Michael FirbankJehill ParikhNicholas MurphyAlison KillenCharlotte L. AllanDaniel CollertonAndrew M. BlamireJohn‐Paul Taylor
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Abstract:
Objective
To investigate the relationship between visual hallucinations in Parkinson disease (PD) and levels of γ-aminobutyric acid (GABA) in the primary visual cortex.Methods
We utilized magnetic resonance spectroscopy to investigate occipital GABA levels in 36 participants with PD, 19 with and 17 without complex visual hallucinations, together with 20 healthy controls without hallucinations. In addition, we acquired T1-weighted MRI, whole-brain fMRI during a visual task, and diffusion tensor imaging.Results
We found lower GABA+/creatine in PD with visual hallucinations (0.091 ± 0.010) vs those without (0.101 ± 0.010) and controls (0.099 ± 0.010) (F2,49 = 4.5; p = 0.016). Reduced gray matter in the hallucinations group was also observed in the anterior temporal lobe. Although there were widespread reductions in white matter integrity in the visual hallucinations group, this was no longer significant after controlling for cognitive function.Conclusions
The data suggest that reduced levels of GABA are associated with visual hallucinations in PD and implicate changes to the ventral visual stream in the genesis of visual hallucinations. Modulation of visual cortical excitability through, for example, pharmacologic intervention, may be a promising treatment avenue to explore.Keywords:
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Visual hallucinations may occur in association with damage to any part of the visual pathway. Charles Bonnet syndrome (CBS) is characterized by vivid visual hallucinations caused by injury to the visual system, while other cognitive functions are preserved. We report on the clinical and neuro-imaging findings of two patients with CBS after acute stroke. The lesions were located bilaterally in the occipital lobes of both patients, although the lesion in patient 1 extended beyond the occipital lobe. In patient 1, moving hallucinations persisted for 9 months after symptom onset, while in patient 2, static hallucinations completely disappeared 7 days after the first hallucination. The latter case had a more extensive lesion on brain magnetic resonance imaging. Our cases suggest that the clinical course of CBS is variable irrespective of cortical lesion size, although this must be confirmed with more patients in the future. Key words: Visual hallucinations; Charles-Bonnet syndrome; Occipital lobe
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Charles Bonnet Syndrome (CBS) is a disorder with visual deficit and complex recurrent visual hallucination in conscious patients, described for the first time by Charles Bonnet. It has been found in association with variable pathologic conditions of the eyes, central visual pathways and occipital lobe. Occipital lobe lesion is an important cause of visual field deficit associated with elementary simple hallucinations, whereas complex hallucinations are related to occipitotemporal and occipitoparietal visual association neocortex damage.
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The authors present three cases of hospitalized patients on a geriatric psychiatry floor who were found to have previously undiagnosed occipital lobe infarctions associated with visual manifestations. The manifestations discussed are visual field defects, visual hallucinations, and color anomia. The incidence of undiagnosed occipital lobe infarctions and the contribution of these infarctions to visual perception changes in this patient population are unknown. The authors suggest that for patients who present with visual perception changes, a high index of suspicion for occipital lobe infarction should be maintained. Careful visual field testing is an essential part of the admitting work-up for hospitalized geriatric patients. ( J Geriatr Psychiatry Neurol 1988;1:231-234).
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Backgound: Visual hallucinations (VH) occur in about 25% of patients with Parkinson's disease (PD). However, the pathophysiological mechanisms of VH in PD are not well understood.
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JAMES CRAIG,1in 1836, is credited with the first recorded case of visual hallucinations with postmortem findings of a lesion of an occipital lobe. His patient complained of seeing figures on the left with eyes open or closed over a 17-year period. At necropsy, a cavity, probably a thrombotic lesion, was found in the left occipital lobe (if the lesion was correctly recorded, the case was one of ipsilateral hallucinations). Fifty years later Seguin2reported that hallucinations always appear in the hemianoptic field. Since these reports, there has been much discussion in the literature, with no general agreement as to whether or not the occipital lobe can produce formed hallucinations,3whether the hallucinations have any lateralizing value,4whether other cortical areas can produce visual hallucinations,5and whether the degree of form taken on by the hallucinations depends on the area involved or on the innate
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In this study of patients with Alzheimer's disease (AD), patients with visual hallucinations were compared with patients who did not have visual hallucinations to determine if selective occipital lobe atrophy is associated with visual hallucinations. Seven AD patients with visual hallucinations were matched by cognitive score to 7 AD patients without visual hallucinations and 3-D MRI images obtained. A ratio of measured occipital volumes to whole brain volumes was compared between the two groups. AD patients with visual hallucinations had a significantly smaller occipital/whole brain ratio than AD patients without visual hallucinations. These results suggest visual hallucinations in AD may be associated with neuropathology of the occipital lobe.
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Charles Bonnet syndrome is an underrecognized disease that involves visual hallucinations in visually impaired patients. We present the cases of three patients who experienced complex visual hallucinations following various pathomechanisms. In two cases, diagnosis showed coexistence of occipital lobe damage with ocular damage, while in the third case it showed occipital lobe damage with retrobulbar optic neuritis. Theories of pathogenesis and the neuroanatomical basis of complex visual hallucinations are discussed and supported by literature review.
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Primary orthostatic tremor is a regular fast lower limb tremor causing unsteadiness on standing.Treatment is generally unsatisfactory.A patient with primary orthostatic tremor who 9 years later developed levodopa responsive idiopathic Parkinson's disease is described.The patient exhibited the classic features of primary orthostatic tremor with relief of the tremor by walking or sitting while treated with levodopa.However, in the "oV" state, when the benefits of levodopa disappeared, this orthostatic tremor was continuous and severely compromised the patient's gait.On the basis of this finding eight patients with primary orthostatic tremor were treated with levodopa.Five patients experienced benefit and elected to remain on long term treatment.This study is the first trial of therapy in primary orthostatic tremor and suggests that levodopa can lead to good symptomatic relief in this potentially disabling condition.
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