Neuropathology of Dementia in Patients with Parkinson's Disease: a Systematic Review of Autopsy Studies
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Neurodegeneration J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp-2019-321111 on 23 August 2019. Downloaded from REVIEW Neuropathology of dementia in patients with Parkinson’s disease: a systematic review of autopsy studies Callum Smith ,1 Naveed Malek,2 Katherine Grosset,1 Breda Cullen ,3 Steve Gentleman,4 Donald G Grosset1 ► Additional material is ABSTRact have other causes of cognitive impairment and published online only. To view Background Dementia is a common, debilitating dementia, such as comorbid Alzheimer’s disease please visit the journal online (http:// dx. doi. org/ 10. 1136/ feature of late Parkinson’s disease (PD). PD dementia (AD) or cerebrovascular disease. These pathologies jnnp- 2019- 321111). (PDD) is associated with α-synuclein propagation, but may be difficult to identify in vivo, as the clinical coexistent Alzheimer’s disease (AD) pathology may features often overlap with those of PDD, and there 1 Department of Neurology, coexist. Other pathologies (cerebrovascular, transactive are no definitive biomarkers. The differentiation Institute of Neurosciences, response DNA-binding protein 43 (TDP-43)) may of dementia type is an important consideration in Queen Elizabeth University Hospital, Glasgow, UK also influence cognition.W e aimed to describe the clinical research, as treatments under development 2Department of Neurology, neuropathology underlying dementia in PD. are specifically targeted against abnormal accumu- Ipswich Hospital NHS Trust, Methods Systematic review of autopsy studies lation of α-synuclein, which is the pathological Ipswich, UK 3 3 published in English involving PD cases with dementia. hallmark of PDD and DLB, or tau or amyloid-β, Institute of Health and 4 5 Wellbeing, College of Medical, Comparison groups included PD without dementia, AD, which underlie AD. A better understanding of the Veterinary, and Life Sciences, dementia with Lewy bodies (DLB) and healthy controls. contribution of different pathological substrates to University of Glasgow, Glasgow, Results 44 reports involving 2002 cases, 57.2% the development of dementia in PD would be useful UK 4 with dementia, met inclusion criteria. While limbic and for the planning and analysis of the efficacy of these Neuropathology Unit, Division neocortical α-synuclein pathology had the strongest of Brain Sciences, Department new treatments. of Medicine, Imperial College association with dementia, between a fifth and a third Autopsy studies are the definitive approach to copyright. London, London, UK of all PD cases in the largest studies had comorbid AD. identify the pathological basis of dementia in PD. In PD cases with dementia, tau pathology was moderate They also ensure that the clinical diagnosis of PD Correspondence to or severe in around a third, and amyloid-β pathology is accurate, which is important given known diag- Mr Callum Smith, Neurology, was moderate or severe in over half. Amyloid-β was nostic error rates in vivo.6 7 We conducted a system- University of Glasgow, Glasgow associated with a more rapid cognitive decline and G51 4TF, UK; c. smith. 3@ atic review of autopsy studies in PD cases with research. gla. ac. uk earlier mortality, and in the striatum, distinguished dementia, to define the relative role of α-synuclein, PDD from DLB. Positive correlations between multiple tau, amyloid-β and other pathologies, including Received 30 April 2019 measures of α-synuclein, tau and amyloid-β were transactive response DNA-binding protein 43 Revised 15 July 2019 found. Cerebrovascular and TDP-43 pathologies did Accepted 14 August 2019 (TDP-43) and cerebrovascular disease, in the aeti- not generally contribute to dementia in PD. TDP-43 and ology of cognitive decline in PD. http://jnnp.bmj.com/ amyloid angiopathy correlated with coexistent Alzheimer PD is pathologically defined by two key features. pathology. Degeneration of the nigrostriatal dopaminergic Conclusions While significantα -synuclein pathology system underlies the progressive motor syndrome is the main substrate of dementia in PD, coexistent that clinically defines the disease.8 Accumulation pathologies are common. In particular, tau and of misfolded, insoluble aggregates of α-synuclein amyloid-β pathologies independently contribute to the protein in the neuronal perikarya (Lewy bodies) development and pattern of cognitive decline in PD. and processes (Lewy neurites) is the second hall- Their presence should be assessed in future clinical trials on September 28, 2021 by guest. Protected mark. According to the Braak staging model for PD where dementia is a key outcome measure. (Braak-PD staging), α-synuclein pathology spreads Trial registration number CRD42018088691. in a stereotypical, caudal-to-rostral pattern in PD, from the brainstem through the limbic system to the neocortex. Propagation of α-synuclein aggregates © Author(s) (or their INTRODUCTION to the neocortical regions is the main substrate of 1 2 employer(s)) 2019. No Cognitive impairment, including dementia, is a cognitive decline in PDD and DLB. 9 commercial re-use. See rights common and debilitating feature in patients with PDD is neuropathologically distinct from AD, and permissions. Published the most common cause of dementia. Like PD, by BMJ. Parkinson’s disease (PD). PD dementia (PDD) is distinguished from dementia with Lewy bodies AD is defined at autopsy by two hallmark lesions. To cite: Smith C, Malek N, (DLB) by the relative timing of the onset of cogni- Neurofibrillary tangles are insoluble, intraneu- Grosset K, et al. J Neurol tive symptoms versus motor signs. In PDD, the ronal bundles of hyperphosphorylated tau protein. Neurosurg Psychiatry Epub ahead of print: [please onset of dementia is usually several years after Amyloid-β plaques are extraneuronal structures include Day Month Year]. PD diagnosis; in DLB, cognitive symptoms occur composed primarily of amyloid-β peptide. ‘Neuritic doi:10.1136/jnnp-2019- within 1 year of the diagnosis of parkinsonism, plaques’ are amyloid-β aggregates with dystrophic 321111 or precedes it.1 2 However, patients with PD may tau-positive neurites that are characteristic of AD. Smith C, et al. J Neurol Neurosurg Psychiatry 2019;0:1–10. doi:10.1136/jnnp-2019-321111 1 Neurodegeneration J Neurol Neurosurg Psychiatry: first published as 10.1136/jnnp-2019-321111 on 23 August 2019. Downloaded from Braak staging for tau pathology10 defines the spread of tau-pos- and reporting bias, using a modified version of the semiquantita- itive tangles and neuropil threads from the transentorhinal tive Cochrane tool.16 The initial plan to use a modified Newcas- cortex (stages I–II), into the entorhinal cortex and hippocampus tle-Ottawa scale for this purpose was abandoned due to concerns (stages III and IV), and finally to neocortical areas. Amyloid-β about the scale’s validity.17 Eligible studies were included in the pathology is described in five Thal phases,11 from the neocortex review regardless of risk of bias. to the entorhinal cortex and subcortical nuclei, and finally to Some reports used the same cases; in determining the sample the brainstem and cerebellum. The Consortium to Establish a size of all studies combined, these cases were only counted once. Registry for Alzheimer’s Disease (CERAD) protocol12 is widely Partial overlap between studies was not subjected to any adjust- used to grade the severity of neuritic plaques. ment because of the small numbers involved. In generating the In addition to Lewy and Alzheimer type abnormalities, various bar charts to describe the severity of Alzheimer pathology, it was other pathologies can underlie dementia. TDP-43 aggregates sometimes necessary to impute data where categories in the orig- contribute to cognitive decline in most forms of frontotemporal inal report (eg, absent and mild) had been collapsed. Values for dementia,13 and cerebrovascular disease (infarcts, haemorrhages imputation were based on average values when all studies were and white matter lesions) contributes to vascular dementia. The combined. Aggregation was done for each bar chart based on specific pathology underlying vascular dementia varies, but raw data. primary causes are cerebral amyloid angiopathy (CAA), athero- 14 sclerosis, and cerebral small vessel disease. RESULTS This novel systematic review included autopsy studies of Study selection and characteristics pathologically verified PD cases with a history of dementia. The Electronic searching retrieved 1552 records, and 14 more primary objective was to define the extent of Lewy, Alzheimer were identified from hand searching. Excluding duplicates and other pathologies (cerebrovascular, TDP-43) in cases of PD and non-human studies, 1519 records underwent preliminary with dementia. screening; 84 were potentially relevant and were read in full. In all, 40 of these were discarded, in most cases due to the lack of relevant detail or PD cases with dementia. Ultimately, 44 articles METHODS involving 41 study groups were included (figure 1). Inter-rater This review was conducted in accordance with the Preferred 15 agreement was 96.8% at initial screening, and 93.6% at the full- Reporting Items for Systematic Reviews and Meta-Analyses. text stage. The protocol was predefined and registered with the Centre for The 44 reports involved 2002 cases with clinically diagnosed Reviews and Dissemination’s International Prospective Register and pathologically verified PD, 1145 (57.2%) of whom had of Systematic Reviews at www. crd. york. ac.uk/ prospero/ on dementia. Dementia was primarily a clinical