After 20 years follow-up of newly diagnosed patients with Parkinson's disease (PD), 100 of 136 (74%) have died. The mortality rate fell in the first 3 years of treatment, then rose compared to the general population, the standardized mortality ratio from 15 to 20 years reaching 3.1. Drug induced dyskinesia and end of dose failure were experienced by most patients, but the main current problems relate to the non-levodopa responsive features of the disease. Dementia is present in 83% of 20-year survivors. Dementia correlates with increasing age and probably reflects an interplay of multiple pathologies. Seventeen people with dementia had postmortems. Eight had diffuse Lewy bodies as the only cause of dementia, while others had mixed neuropathology. Only one person lives independently and 48% are in nursing homes. Excessive daytime sleepiness is noted in 70%, falls have occurred in 87%, freezing in 81%, fractures in 35%, symptomatic postural hypotension in 48%, urinary incontinence in 71%, moderate dysarthria in 81%, choking in 48%, and hallucinations in 74%. The challenge is to understand the cellular mechanisms underlying the diverse features of advanced PD that go far beyond a lack of dopamine.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/mds.21956

The Sydney Multicenter Study of Parkinson's Disease : The Inevitability of Dementia at 20 years

Prevalence rates of depressive disorders in Parkinson's disease (PD) vary widely across studies, ranging from 2.7% to more than 90%. The aim of this systematic review was to calculate average prevalences of depressive disorders taking into account the different settings and different diagnostic approaches of studies. Using Medline on Pubmed, a systematic literature search was carried out for studies of depression in Parkinson's disease. A total of 104 articles were included and assessed for quality; 51 articles fulfilled the quality criteria. Multiple publications from the same database were not included in the meta-analysis. In the remaining 36 articles, the weighted prevalence of major depressive disorder was 17% of PD patients, that of minor depression 22% and dysthymia 13%. Clinically significant depressive symptoms, irrespective of the presence of a DSM defined depressive disorder, were present in 35%. In studies using a (semi) structured interview to establish DSM criteria, the reported prevalence of major depressive disorder was 19%, while in studies using DSM criteria without a structured interview, the reported prevalence of major depressive disorder was 7%. Population studies report lower prevalence rates for both major depressive disorder and the clinically significant depressive symptoms than studies in other settings. This systematic review suggests that the average prevalence of major depressive disorder in PD is substantial, but lower than generally assumed.

A systematic review of prevalence studies of dementia in Parkinson's disease.

Bovine spongiform encephalopathy (BSE) and human Creutzfeldt-Jakob disease (CJD) are among the most notable central nervous system degenerative disorders caused by prions. CJD may present as a sporadic, genetic, or infectious illness. Prions are transmissible particles that are devoid of nucleic acid and seem to be composed exclusively of a modified protein (PrP Sc ). The normal, cellular prion protein (PrP C ) is converted into PrP Sc through a posttranslational process during which it acquires a high β-sheet content. It is thought that BSE is a result of cannibalism in which faulty industrial practices produced prion-contaminated feed for cattle. There is now considerable concern that bovine prions may have been passed to humans, resulting in a new form of CJD.

https://science.sciencemag.org/content/sci/278/5336/245.full.pdf

Prion Diseases and the BSE Crisis

Progressive supranuclear palsy (Steele et al.) has a characteristic pattern of dementia: (1) forgetfulness, (2) slowing of thought processes, (3) emotional or personality changes (apathy or depression with occasional outbursts of irritability), and (4) impaired ability to manipulate acquired knowledge. In many neurological disease states associated with subcortical pathology a similar pattern of dementia exists. The neurobehavioural changes of progressive supranuclear palsy thus typify a clinical pattern which may be referred to as subcortical dementia. The subcortical dementias have a striking clinical resemblance to the dementia which occurs after bifrontal lobe disease. However, the subcortical dementias can be clearly distinguished clinically from cortical dementias, other than frontal dementias. We propose as a tentative hypothesis that there may be common pathophysiological mechanisms underlying the subcortical dementias—in particular, disturbances of timing and activation. There are immediate practical implications of this hypothesis: drugs which have an effect on subcortical timing and activating mechanisms may be useful in the treatment of subcortical dementias.

https://jnnp.bmj.com/content/jnnp/37/2/121.full.pdf

The `subcortical dementia' of progressive supranuclear palsy

Background: Dementia is a frequent complication of idiopathic parkinsonism or PD, usually occurring later in the protracted course of the illness. The primary site of neuropathologic change in PD is the substantia nigra, but the neuropathologic and molecular basis of dementia in PD is less clear. Although Alzheimer’s pathology has been a frequent finding, recent advances in immunostaining of α-synuclein have suggested the possible importance of cortical Lewy bodies (CLBs) in the brains of demented patients with PD. Methods: The brains of 22 demented and 20 nondemented patients with a clinical and neuropathologic diagnosis of PD were evaluated with standard neuropathologic techniques. In addition, CLBs and dystrophic neurites were identified immunohistochemically with antibodies specific for α-synuclein and ubiquitin; plaques and tangles were identified by staining with thioflavine S. Associations between dementia status and pathologic markers were tested with logistic regression. Results: CLBs positive for α-synuclein are highly sensitive (91%) and specific (90%) neuropathologic markers of dementia in PD and slightly more sensitive than ubiquitin-positive CLBs. They are better indicators of dementia than neurofibrillary tangles, amyloid plaques, or dystrophic neurites. Conclusion: CLBs detected by α-synuclein antibodies in patients with PD are a more sensitive and specific correlate of dementia than the presence of Alzheimer’s pathology, which was present in a minority of the cases in this series.

R. W. Hornabrook

Papers

The prevalence, natural history and dementia of parkinson's disease

Kuru--a subacute cerebellar degeneration. The natural history and clinical features.