110 Atrophy of the mediodorsal thalamus is associated with visual hallucinations in lewy body diseases

IntroductionAlthough limbic system dysfunction has been thought to underlie visual hallucinations in patients with Lewy body disorders, neuropathology within thalamic structures subserving limbic functions have not been examined. In this study, we assessed the degree of neuronal degeneration in thalamic regions involved in perceptual integration in patients with Parkinson’s disease (PD), Parkinson’s disease dementia (PDD) and dementia with Lewy bodies (DLB).MethodsPost-mortem samples were acquired from twenty-four individuals with Lewy body disease (5 PD, 9 PDD, 10 DLB) and 10 age-matched controls. The anterior principal (AP) and mediodorsal (MD) thalamic nuclei were delineated and analysed using stereological and quantitative neuropathological techniques.ResultsVolume loss within the MD nucleus was observed in patients with DLB (31%) and PDD (18%) but not PD compared to controls (ANOVA, p<0.05). The atrophy was significantly greater in those patients with hallucinations than those without (p<0.05). Somal atrophy was seen in all patient groups and did not correlate with volume loss or visual hallucinations. Interestingly, there was no neuronal loss in this region compared to controls in the Lewy body disease groups. Analysis of the AP nucleus revealed similar patterns of volume loss but with somal atrophy only in patients with PDD and DLB. Both these measures did not correlate significantly with visual hallucinations, but was significantly different in patients with dementia compared to PD only and controls (p<0.05).ConclusionThese results suggest that afferent denervation of the mediodorsal thalamus may contribute to visual hallucinations. This appears to support models that implicate upstream components of the limbic circuitry in the generation of this phenomenon.