Visual hallucinations in dementia with Lewy bodies: transcranial magnetic stimulation study

Abstract

BackgroundThe aetiology of visual hallucinations is poorly understood in dementia with Lewy bodies. Pathological alterations in visual cortical excitability may be one contributory mechanism.AimsTo determine visual cortical excitability in people with dementia with Lewy bodies compared with aged-matched controls and also the relationship between visual cortical excitability and visual hallucinations in dementia with Lewy bodies.MethodVisual cortical excitability was determined by using transcranial magnetic stimulation (TMS) applied to the occiput to elicit phosphenes (transient subjective visual responses) in 21 patients with dementia with Lewy bodies and 19 age-matched controls.ResultsPhosphene parameters were similar between both groups. However, in the patients with dementia with Lewy bodies, TMS measures of visual cortical excitability correlated strongly with the severity of visual hallucinations (P = 0.005). Six patients with dementia with Lewy bodies experienced visual hallucination-like phosphenes (for example, seeing people or figures on stimulation) compared with none of the controls (P = 0.02).ConclusionsIncreased visual cortical excitability in dementia with Lewy bodies does not appear to explain visual hallucinations but it may be a marker for their severity.

Functional Disconnectivity during Inter-Task Resting State in Dementia with Lewy Bodies

“…In contrast, the few functional MRI studies on this topic reported a relative preservation of functional activity in lower visual areas, suggesting that the visuoperceptual impairment in these patients is rather related to disturbances in higher visual areas [13]. This hypothesis is supported by the results of other studies showing the absence of significant grey matter atrophy in the occipital lobe in DLB patients [14], and no difference in visual-cortical excitability compared to controls [15]. …”

Visual Hallucinations in PD and Lewy Body Dementias: Old and New Hypotheses

“…In addition, elicitation of reliable VH in an experimental setting would allow the development of powerful new paradigms to explore the underlying pathophysiology of VH in PD and Lewy body dementias. In the study by Taylor et al [106] occipital transcranial magnetic stimulation provided an external method to generate VH in DLB although these occurred infrequently and only in a minority of patients. Another technique, developed by our group, using virtual reality presentation (Box 3) may provide a promising new approach to reliably testing VH in an experimental setting.…”

“…Lower visual areas (e.g. V1 through to V3) appear to be less implicated as: 1) there appears to be a perseveration of these areas both at a macro and micro-structural level [100][101][102], for example, in DLB; 2) perfusion and functional imaging have suggested visuo-perceptual deficits [103] and VH are associated with higher visual areas [104,105] and the threshold of occipital transcranial magnetic stimulation (TMS) induced phosphenes, a marker of lower visual area cortical excitability, appears similar in DLB to aged controls [106]. The authors of the latter observation reported an association between visual cortical excitability with TMS and the frequency and severity of VH in DLB and they provocatively suggested that the intrinsic excitability level of lower visual areas may be inherent to the individual's 'premorbid' neurobiology and that differing phosphene thresholds may contribute to the predilection in some individuals towards VH when they develop alpha-synuclein neuropathology.…”

Advances In the Treatment of Visual Hallucinations In Neurodegenerative Diseases

“…In this regard, neuroimaging, neurophysiological and neuropathological/neurochemical studies have begun to provide powerful insights in the etiology of visual hallucinations [67][68][69][70][71]. For example, postmortem and neuroimaging studies in LBD patients have found that alterations in both nicotinic and muscarinic receptors are associated with visual hallucinations [45,71]. New pharmacological agents that target these receptor systems may therefore be useful future treatments.…”