A historical analysis of the relationship between encephalitis lethargica and postencephalitic parkinsonism: A complex rather than a direct relationship

Update: Descriptive epidemiology of Parkinson disease

We review the descriptive epidemiology of Parkinson disease (PD). PD is a prevalent neurologic disorder in high Socio-Demographic Index (SDI) nations with rising prevalence in low and middle SDI nations. PD became a prevalent disorder in high SDI nations during the 20th century. Population growth, population aging, and increased disease duration are major drivers of rising PD prevalence. Exposure to industrial toxicants may also be a contributor to rising PD prevalence. PD is an age-related disorder with incidence likely peaking in the 8th decade of life and prevalence in the 9th decade of life. PD is notable for significant sex difference in PD risk with greater risk in men. There may be ancestral differences in PD prevalence and risk. PD is associated with moderately increased mortality though this may be underestimated. Despite significant research, there is considerable uncertainty about basic features of PD epidemiology.

Viruses, parkinsonism and Parkinson's disease: the past, present and future

Parkinsonism secondary to viral infections is not an uncommon occurrence and has been brought under the spotlight with the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. A variety of viruses have been described with a potential of inducing or contributing to the occurrence of parkinsonism and Parkinson's disease (PD), although the relationship between the two remains a matter of debate originating with the description of encephalitis lethargica in the aftermath of the Spanish flu in 1918. While some viral infections have been linked to an increased risk for the development of PD, others seem to have a causal link with the occurrence of parkinsonism. Here, we review the currently available evidence on viral-induced parkinsonism with a focus on potential pathophysiological mechanisms and clinical features. We also review the evidence on viral infections as a risk factor for developing PD and the link between SARS-CoV-2 and parkinsonism, which might have important implications for future research and treatments.

Microglial Priming in Infections and Its Risk to Neurodegenerative Diseases

Infectious diseases of different etiologies have been associated with acute and long-term neurological consequences. The primary cause of these consequences appears to be an inflammatory process characterized primarily by a pro-inflammatory microglial state. Microglial cells, the local effectors' cells of innate immunity, once faced by a stimulus, alter their morphology, and become a primary source of inflammatory cytokines that increase the inflammatory process of the brain. This inflammatory scenario exerts a critical role in the pathogenesis of neurodegenerative diseases. In recent years, several studies have shown the involvement of the microglial inflammatory response caused by infections in the development of neurodegenerative diseases. This has been associated with a transitory microglial state subsequent to an inflammatory response, known as microglial priming, in which these cells are more responsive to stimuli. Thus, systemic inflammation and infections induce a transitory state in microglia that may lead to changes in their state and function, making priming them for subsequent immune challenges. However, considering that microglia are long-lived cells and are repeatedly exposed to infections during a lifetime, microglial priming may not be beneficial. In this review, we discuss the relationship between infections and neurodegenerative diseases and how this may rely on microglial priming.

René Cruchet (1875-1959), beyond encephalitis lethargica

René Cruchet (1875-1959) was a pediatrician from Bordeaux known for his seminal description of encephalitis lethargica during World War I, at the same time as Constantin von Economo (1876-1931) in Vienna published his own description, which, unlike Cruchet's description, provided precious anatomopathological data in addition to the clinical data. Cruchet was interested in tics and dystonia and called for treatment using behavioral psychotherapy that was, above all, repressive. Cruchet was also a physiologist and an innovator in aeronautic medicine-notably, he helped pioneer the study of "aviator's disease" during World War I. Moreover, he possessed an encyclopedic knowledge, while publishing in all medical fields, writing philosophical texts as well as travel logs.

COVID-19: The cynosure of rise of Parkinson's disease

Parkinson's disease (PD) is one of the most common age-related disorders globally. The pathophysiological mechanisms and precipitating factors underlying PD manifestations, including genetic and environmental parameters, inflammation/stress and ageing, remain elusive. Speculations about whether the Coronavirus Disease 2019 (Covid-19) pandemic could be a pivotal factor in affecting the prevalence and severity of PD or triggering a wave of new-onset parkinsonism in both the near and distant future have recently become very popular, with researchers wondering if there is a changing trend in current parkinsonism cases. Could the current understanding of the Covid-19 pathophysiology provide clues for an impending rise of parkinsonism cases in the future? Are there any lessons to learn from previous pandemics? Our aim was to look into these questions and available current literature in order to investigate if Covid-19 could constitute a cardinal event affecting the parkinsonism landscape.

COVID-19 and Vaccination in the Setting of Neurologic Disease: An Emerging Issue in Neurology

The COVID-19 pandemic caused by the SARS-CoV-2 virus has left many unanswered questions for patients with neurological disorders and the providers caring for them. Elderly and immunocompromised patients are at increased risk for severe symptoms due to COVID-19, and the virus may increase symptoms of underlying neurological illness, particularly for those with significant bulbar and respiratory weakness or other neurologic disability. Emerging SARS-CoV-2 vaccines offer substantial protection from symptomatic infection, but both patients and providers may have concerns regarding theoretical risks of vaccination, including vaccine safety and efficacy in the context of immunotherapy and the potential for precipitating or exacerbating neurological symptoms. In this statement on behalf of the Quality Committee of the AAN we review the current literature, focusing on COVID-19 infection in adults with neurological disease, in order to elucidate risks and benefits of vaccination in these individuals. Based on existing evidence, neurologists should recommend COVID-19 vaccination to their patients. For those patients being treated with immunotherapies, attention should be paid to timing of vaccination with respect to treatment and the potential for an attenuated immune response.

No Metagenomic Evidence of Causative Viral Pathogens in Postencephalitic Parkinsonism Following Encephalitis Lethargica

Postencephalitic parkinsonism (PEP) is a disease of unknown etiology and pathophysiology following encephalitis lethargica (EL), an acute-onset polioencephalitis of cryptic cause in the 1920s. PEP is a tauopathy with multisystem neuronal loss and gliosis, clinically characterized by bradykinesia, rigidity, rest tremor, and oculogyric crises. Though a viral cause of EL is likely, past polymerase chain reaction-based investigations in the etiology of both PEP and EL were negative. PEP might be caused directly by an unknown viral pathogen or the consequence of a post-infectious immunopathology. The development of metagenomic next-generation sequencing in conjunction with bioinformatic techniques has generated a broad-range tool for the detection of unknown pathogens in the recent past. Retrospective identification and characterization of pathogens responsible for past infectious diseases can be successfully performed with formalin-fixed paraffin-embedded (FFPE) tissue samples. In this study, we analyzed 24 FFPE brain samples from six patients with PEP by unbiased metagenomic next-generation sequencing. Our results show that no evidence for the presence of a specific or putative (novel) viral pathogen was found, suggesting a likely post-infectious immune-mediated etiology of PEP.

Can COVID-19 accelerate neurodegeneration?

COVID-19 may accelerate neurodegeneration in patients with neurodegenerative disease.

Genetic and Environmental Factors in Parkinson's Disease Converge on Immune Function and Inflammation

Idiopathic Parkinson's disease (iPD) is a movement disorder characterized by the degeneration of dopaminergic neurons and aggregation of the protein α-synuclein. Patients with iPD vary in age of symptom onset, rate of progression, severity of motor and non-motor symptoms, and extent of central and peripheral inflammation. Genetic and environmental factors are believed to act synergistically in iPD pathogenesis. We propose that environmental factors (pesticides and infections) increase the risk for iPD via the immune system and that the role of PD risk genes in immune cells is worthy of investigation. This review highlights the major PD-relevant genes expressed in immune cells and key environmental factors that activate immune cells and, alone or in combination with other factors, may contribute to iPD pathogenesis. By reviewing these interactions, we seek to enable the future development of immunomodulatory approaches to prevent or delay onset of iPD. © 2020 International Parkinson and Movement Disorder Society.

Neurodegeneration and Inflammation-An Interesting Interplay in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder, caused by, so far, unknown pathogenetic mechanisms. There is no doubt that pro-inflammatory immune-mediated mechanisms are pivotal to the pathogenicity and progression of the disease. In this review, we highlight the binary role of microglia activation in the pathophysiology of the disorder, both neuroprotective and neuromodulatory. We present how the expression of several cytokines implicated in dopaminergic neurons (DA) degeneration could be used as biomarkers for PD. Viral infections have been studied and correlated to the disease progression, usually operating as trigger factors for the inflammatory process. The gut-brain axis and the possible contribution of the peripheral bowel inflammation to neuronal death, mainly dopaminergic neurons, seems to be a main contributor of brain neuroinflammation. The role of the immune system has also been analyzed implicating a-synuclein in the activation of innate and adaptive immunity. We also discuss therapeutic approaches concerning PD and neuroinflammation, which have been studied in experimental and in vitro models and data stemming from epidemiological studies.

Disruption of cellular proteostasis by H1N1 influenza A virus causes α-synuclein aggregation

Neurodegenerative diseases feature specific misfolded or misassembled proteins associated with neurotoxicity. The precise mechanisms by which protein aggregates first arise in the majority of sporadic cases have remained unclear. Likely, a first critical mass of misfolded proteins starts a vicious cycle of a prion-like expansion. We hypothesize that viruses, having evolved to hijack the host cellular machinery for catalyzing their replication, lead to profound disturbances of cellular proteostasis, resulting in such a critical mass of protein aggregates. Here, we investigated the effect of influenza virus (H1N1) strains on proteostasis of proteins associated with neurodegenerative diseases in Lund human mesencephalic dopaminergic cells in vitro and infection of Rag knockout mice in vivo. We demonstrate that acute H1N1 infection leads to the formation of α-synuclein and Disrupted-in-Schizophrenia 1 (DISC1) aggregates, but not of tau or TDP-43 aggregates, indicating a selective effect on proteostasis. Oseltamivir phosphate, an antiinfluenza drug, prevented H1N1-induced α-synuclein aggregation. As a cell pathobiological mechanism, we identified H1N1-induced blocking of autophagosome formation and inhibition of autophagic flux. In addition, α-synuclein aggregates appeared in infected cell populations connected to the olfactory bulbs following intranasal instillation of H1N1 in Rag knockout mice. We propose that H1N1 virus replication in neuronal cells can induce seeds of aggregated α-synuclein or DISC1 that may be able to initiate further detrimental downstream events and should thus be considered a risk factor in the pathogenesis of synucleinopathies or a subset of mental disorders. More generally, aberrant proteostasis induced by viruses may be an underappreciated factor in initiating protein misfolding.

Secondary parkinsonism due to drugs, vascular lesions, tumors, trauma, and other insults

In addition to neurodegenerative disorders, there are many secondary forms of parkinsonism. The most common cause for secondary parkinsonism is the intake of distinct drugs. Neuroleptics and calcium channel blockers have been mainly described to induce parkinsonism, but also other drugs were suspected to cause or worsen parkinsonism. Another common cause for secondary parkinsonism are vascular lesions (i.e. vascular parkinsonism). Furthermore, also brain tumors have been described as rare causes for parkinsonism. Moreover, parkinsonism can be caused by chronic traumatic encephalopathy, which is a special case, since secondary insults to the brain leads to the occurrence of a neuropathologically defined disease. Other rare causes for secondary parkinsonism are lesions caused by infectious or immunological diseases as well as toxins or street drugs.

Diabetes, a Contemporary Risk for Parkinson's Disease: Epidemiological and Cellular Evidences

Diabetes mellitus (DM), a group of diseases characterized by defective glucose metabolism, is the most widespread metabolic disorder affecting over 400 million adults worldwide. This pathological condition has been implicated in the pathogenesis of a number of central encephalopathies and peripheral neuropathies. In further support of this notion, recent epidemiological evidence suggests a link between DM and Parkinson’s disease (PD), with hyperglycemia emerging as one of the culprits in neurodegeneration involving the nigrostriatal pathway, the neuroanatomical substrate of the motor symptoms affecting parkinsonian patients. Indeed, dopaminergic neurons located in the mesencephalic substantia nigra appear to be particularly vulnerable to oxidative stress and degeneration, likely because of their intrinsic susceptibility to mitochondrial dysfunction, which may represent a direct consequence of hyperglycemia and hyperglycemia-induced oxidative stress. Other pathological pathways induced by increased intracellular glucose levels, including the polyol and the hexosamine pathway as well as the formation of advanced glycation end-products, may all play a pivotal role in mediating the detrimental effects of hyperglycemia on nigral dopaminergic neurons. In this review article, we will examine the epidemiological as well as the molecular and cellular clues supporting the potential susceptibility of nigrostriatal dopaminergic neurons to hyperglycemia.

Centenary of Tretiakoff's thesis on the morphology of Parkinson's disease, evolved on the grounds of encephalitis lethargica pathology

In his Thèse de Paris (1919) Konstantin Tretiakoff (1892-1956) described the two main morphological lesions in Parkinson's disease: the loss of pigmented nerve cells in the Substantia nigra and the intracellular inclusion bodies in idiopathic paralysis agitans, calling them "Corps de Lewy," which already had been described by F. H. Lewy in 1912. Tretiakoff's findings on idiopathic Parkinson's disease were confirmed years later by Rolf Hassler in his dissertation on anatomy and pathology of Substantia nigra in Berlin (1938, 1939). German authors in the 1920s underestimated the significance of both findings (Bielschowsky, 1922; Lewy 1923/1924; Spatz 1927), especially Lewy himself. Lewy (1923) and other German neurologists and neuropathologists like Felix Stern (1922, 1928), Goldstein (1922), and Spatz (1927; Luksch & Spatz, 1923) acknowledged the typical Nigra-lesions only for postencephalitic Parkinsonism. It is argued that Tretiakoff's selective attention for the Substantia nigra was guided by the frequency of epidemic encephalitis lethargica and its preponderance of nigral pathology. This impression can be derived from Tretiakoff's early paper on that disease (Marie & Tretiakoff, 1918) and from Paul Foley's opus magnum (2018). Two outstanding neurologists dedicated to this issue are called into memory: Gabrielle Lévy, the successor of Tretiakoff in the Salpêtrière laboratory, and Felix Stern, who died in 1942 as a victim of Nazi terror. The eponym Lewy-bodies went back to Lafora and Tretiakoff ("Corps de Lewy"). Newly expressed doubts about Lewy's primacy or Lafora's credit for the eponym (Lafora-bodies since 1911) can be refuted with the studies of Greenfield and Bosanquet (1953) and Greenfield (1963) by illustrating their different staining properties.

La Von Economo’s encephalitis lethargica and the Spanish flu pandemic in Bogotá and Medellín (Colombia): An historic review one hundred years after

Von Economo’s encephalitis is a neuropsychiatric disorder of possible autoimmune origin, which affects basal ganglia. This reaction may occur secondary to infection by different viral or bacterial agents. Given that it appears after the acute episode has disappeared, molecular mimetism has been proposed to explain the autoimmune lesion. Several cases have been reported through time, but it was with the 1918 flu pandemic, known as the Spanish flu, that lethargic encephalitis reached epidemic levels with cases reported until 1923 in various countries. The Spanish flu pandemic appeared in Colombia at the end of 1918 in several cities but it affected especially Bogotá where the highest number of patients and deaths was reported. Our purpose with the present work was to commemorate the arrival of the Spanish flu to our country after one hundred years, as well as to reflect on its main complications, which included some lethargic encepahilitis cases.

Past, present, and future of Parkinson's disease: A special essay on the 200th Anniversary of the Shaking Palsy

This article reviews and summarizes 200 years of Parkinson's disease. It comprises a relevant history of Dr. James Parkinson's himself and what he described accurately and what he missed from today's perspective. Parkinson's disease today is understood as a multietiological condition with uncertain etiopathogenesis. Many advances have occurred regarding pathophysiology and symptomatic treatments, but critically important issues are still pending resolution. Among the latter, the need to modify disease progression is undoubtedly a priority. In sum, this multiple-author article, prepared to commemorate the bicentenary of the shaking palsy, provides a historical state-of-the-art account of what has been achieved, the current situation, and how to progress toward resolving Parkinson's disease. © 2017 International Parkinson and Movement Disorder Society.

Neurosyphilis presenting as parkinsonism

In the postantibiotic era, neurosyphilis continues to have a significant incidence, especially in certain subpopulations. We report, for the first time, neurosyphilis presenting as parkinsonism without more typical neurosyphilitic clinical features. A 53-year-old man developed clinical features of gradual onset consistent with idiopathic Parkinson's disease but was found to have positive treponemal serology and cerebrospinal fluid Venereal Disease Research Laboratory (VRDL) reaction. Antibiotic treatment dramatically improved all the parkinsonian symptoms. However, over the subsequent 15 years, the patient slowly deteriorated again in a manner typical of idiopathic Parkinson's disease. A dopaminergic deficit was demonstrated on ((123)I)FP-CIT SPECT. This is the first report in the postantibiotic era of neurosyphilis presenting as relatively pure parkinsonism. Blood test screening for syphilis is therefore appropriate if there is any clinical doubt about an idiopathic parkinsonian presentation. The patient's late second deterioration may suggest that the neurosyphilitic basal ganglial insult primed or accelerated development of idiopathic-like disease.

Hitler's parkinsonism

Of the multitude of medical and psychiatric conditions ascribed to Hitler both in his lifetime and since his suicide in April 1945, few are more substantiated than parkinsonism. While the timeline of the development of this condition, as well as its etiology, are debated, there is clear evidence for classic manifestations of the disease, most prominently a resting tremor but also stooped posture, bradykinesia, micrographia, and masked facial expressions, with progression steadily seen over his final years. Though ultimately speculation, some have suggested that Hitler suffered from progressive cognitive and mood disturbances, possibly due to parkinsonism, that affected the course of events in the war. Here, the authors discuss Hitler's parkinsonism in the context of the Third Reich and its eventual destruction, maintaining that ultimately his disease had little effect on the end result.

Medical and molecular perspectives into a forgotten epidemic: encephalitis lethargica, viruses, and high-throughput sequencing

The emergence of encephalitis lethargica (EL), an acute-onset polioencephalitis of unknown etiology as an epidemic in the years 1917-1925 is still unexplainable today. Questioned by the first descriptor of EL himself, Constantin von Economo, there has been much debate shrouding a possible role of the "Spanish" H1N1 influenza A pandemic virus in the development of EL. Previous molecular studies employing conventional PCR for the detection of influenza A virus RNA in archived human brain samples from patients who died of acute EL were negative. However, the clinical and laboratory characteristics of EL and its epidemiology are consistent with an infectious disease, and recently a possible enterovirus cause was investigated. With the rapid development of high-throughput sequencing, new information about a possible viral etiology can be obtained if sufficient specimens for analysis were still available today. Here, we discuss the implications of these technologies for the investigation of a possible infectious cause of EL from archived material, as well as a prospectus for future work for acquiring viral nucleic acids from these sources.

The Demise of Poskanzer and Schwab's Influenza Theory on the Pathogenesis of Parkinson's Disease

In 1961, David C. Poskanzer and Robert S. Schwab presented a paper, "Studies in the epidemiology of Parkinson's disease predicting its disappearance as a major clinical entity by 1980." This paper introduced the hypothesis that Parkinson's disease was derived from a single aetiology, the influenza virus. We review the original Poskanzer and Schwab hypothesis that Parkinson's disease was based on the association between the 1918-19 influenza epidemic and the later observation of Parkinsonism in some influenza sufferers. We also further explore the prediction that Parkinson's disease would totally disappear as an entity once original influenza victims were all deceased. Current research has revealed that there are many potential causes and factors important in the occurrence of Parkinson's disease, postencephalitic Parkinsonism, and encephalitis lethargica. Poskanzer and Schwab presented a novel hypothesis; however, it was proven false by a combination of research and time.

Lysosomal storage disorders and Parkinson's disease: Gaucher disease and beyond

Parkinson's disease is associated with mutations in the glucocerebrosidase gene, which result in the enzyme deficiency causing Gaucher disease, the most common lysosomal storage disorder. We have performed an exhaustive literature search and found that additional lysosomal storage disorders might be associated with Parkinson's disease, based on case reports, the appearance of pathological features such as α-synuclein deposits in the brain, and substantia nigra pathology. Our findings suggest that the search for biochemical and cellular pathways that link Parkinson's disease with lysosomal storage disorders should not be limited exclusively to changes that occur in Gaucher disease, such as changes in glucocerebrosidase activity or in glucosylceramide levels, but rather include changes that might be common to a wide variety of lysosomal storage disorders. Moreover, we propose that additional genetic, epidemiological, and clinical studies should be performed to check the precise incidence of mutations in genes encoding lysosomal proteins in patients displaying Parkinson's symptoms.

The diagnosis of postencephalitic parkinsonism at the neurological unit of Boston City Hospital, 1930-1981

The objective of the study is to ascertain the rationale for the diagnosis of postencephalitic parkinsonism (PEP) at Boston City Hospital's Neurological Unit (1930-1981). 5,270 discharge summaries were evaluated for the diagnoses of PEP. Sixteen cases of PEP were identified; the diagnosis of PEP was justified in approximately half of these cases based on the published criteria for distinguishing PEP from Parkinson's disease (PD). In conclusions, the absence of a clear justification for the diagnosis of PEP in many of the 16 cases suggests that the accepted relationship between encephalitis lethargica and PEP may be less definitive than currently believed.