Rapidly progressive dementias and the treatment of human prion diseases

Rapidly progressive dementias - aetiologies, diagnosis and management

Rapidly progressive dementias (RPDs) are a group of heterogeneous disorders that include immune-mediated, infectious and metabolic encephalopathies, as well as prion diseases and atypically rapid presentations of more common neurodegenerative diseases. Some of these conditions are treatable, and some must be diagnosed promptly because of their potential infectivity. Prion disease is considered to be the prototypical RPD, but over the past two decades, epidemiological reports and the identification of various encephalitis-mediating antibodies have led to a growing recognition of other encephalopathies as potential causes of rapid cognitive decline. Knowledge of RPD aetiologies, syndromes and diagnostic work-up protocols will help clinicians to establish an early, accurate diagnosis, thereby reducing morbidity and mortality, especially in immune-mediated and other potentially reversible dementias. In this Review, we define the syndrome of RPD and shed light on its different aetiologies and on secondary factors that might contribute to rapid cognitive decline. We describe an extended diagnostic procedure in the context of important differential diagnoses, discuss the utility of biomarkers and summarize potential treatment options. In addition, we discuss treatment options such as high-dose steroid therapy in the context of therapy and diagnosis in clinically ambiguous cases.

The term ‘rapidly progressive dementia’ (RPD) describes a cognitive disorder with fast progression, leading to dementia within a relatively short time. This Review discusses the wide range of RPD aetiologies, as well as the diagnostic approach and treatment options.

Definitions of rapidly progressive dementia (RPD) vary according to the aetiological background and relate to the speed of cognitive decline, time from first symptom to dementia syndrome and/or overall survival.

RPD can occur in rapidly progressive neurodegenerative diseases, such as prion diseases, or in primarily slowly progressive diseases as a consequence of intrinsic factors or concomitant pathologies.

Besides neurodegenerative diseases, inflammatory (immune-mediated and infectious), vascular, metabolic and neoplastic CNS diseases are important and frequent causes of RPD.

To identify treatable causes of RPD, the technical diagnostic work-up must include MRI and analyses of blood and cerebrospinal fluid, and further diagnostics might be indicated in unclear cases.

Therapeutic options for many non-neurodegenerative causes of RPD are already available; disease-modifying therapies for neurodegenerative RPDs are an important focus of current research and could become a treatment option in the near future.

Understanding Creutzfeldt-Jackob disease from a viewpoint of amyloidogenic evolvability

Creutzfeldt-Jackob disease (CJD), the most common human prion disorder, is frequently accompanied by ageing-associated neurodegenerative conditions, such as Alzheimer’s disease and Parkinson’s disease. Although cross-seeding of amyloidogenic proteins (APs), including amyloid β and α-synuclein, may be critical in the co-morbidity of neurodegenerative disorders, the direct interaction of APs with prion protein (PrP), the central molecule involved in the pathogenesis of CJD, is unlikely. Currently, the nature of this biological interaction and its significance remain obscure. In this context, the objective of the present study is to discuss such interactions from the perspective of amyloidogenic evolvability, a putative function of APs. Hypothetically, both hereditary- and sporadic CJD might be attributed to the role of PrP in evolvability against multiple stressors, such as physical stresses relevant to concussions, which might be manifest through the antagonistic pleiotropy mechanism in ageing. Furthermore, accumulating evidence suggests that PrP- and other APs evolvability may negatively regulate each other. Provided that increased APs evolvability might be beneficial for acquired CJD in young adults, a dose-reduction of α-synuclein, a natural inhibitor of αS aggregation, might be therapeutically effective in upregulating APs evolvability. Collectively, a better understanding of amyloidogenic evolvability may lead to the development of novel therapies for CJD.

Neurotheranostics as personalized medicines

The discipline of neurotheranostics was forged to improve diagnostic and therapeutic clinical outcomes for neurological disorders. Research was facilitated, in largest measure, by the creation of pharmacologically effective multimodal pharmaceutical formulations. Deployment of neurotheranostic agents could revolutionize staging and improve nervous system disease therapeutic outcomes. However, obstacles in formulation design, drug loading and payload delivery still remain. These will certainly be aided by multidisciplinary basic research and clinical teams with pharmacology, nanotechnology, neuroscience and pharmaceutic expertise. When successful the end results will provide "optimal" therapeutic delivery platforms. The current report reviews an extensive body of knowledge of the natural history, epidemiology, pathogenesis and therapeutics of neurologic disease with an eye on how, when and under what circumstances neurotheranostics will soon be used as personalized medicines for a broad range of neurodegenerative, neuroinflammatory and neuroinfectious diseases.

Therapies for prion diseases

Recent advances in understanding of the molecular biology of prion diseases and improved clinical diagnostic techniques might allow researchers to think about therapeutic trials in Creutzfeldt-Jakob disease (CJD) patients. Some attempts have been made in the past and various compounds have been tested in single case reports and patient series. Controlled trials are rare. However, in the past few years, it has been demonstrated that clinical trials are feasible. The clinicians might face several specific problems when evaluating the efficacy of the drug in CJD, such as rareness of the disease, lack of appropriate preclinical tests and heterogeneous clinical presentation in humans. These problems have to be carefully addressed in future.

An Evaluation of Rapidly Progressive Dementia Culminating in a Diagnosis of Creutzfeldt-Jakob Disease

Rapidly progressive dementia is a curious and elusive clinical description of a pattern of cognitive deficits that progresses faster than typical dementia syndromes. The differential diagnosis and clinical workup for rapidly progressive dementia are quite extensive and involve searching for infectious, inflammatory, autoimmune, neoplastic, metabolic, and neurodegenerative causes. We present the case of a previously highly functional 76-year-old individual who presented with a 6-month history of rapidly progressive dementia. His most prominent symptoms were cognitive impairment, aphasia, visual hallucinations, and ataxia. Following an extensive battery of tests in hospital, the differential diagnosis remained probable CJD versus autoimmune encephalitis. He clinically deteriorated and progressed to akinetic mutism and myoclonus. He passed away 8 weeks after his initial presentation to hospital, and an autopsy confirmed a diagnosis of sporadic CJD. We use this illustrative case as a framework to discuss the clinical and diagnostic considerations in the workup for rapidly progressive dementia. We also discuss CJD and autoimmune encephalitis, the two main diagnostic possibilities in our patient, in more detail.

Diagnostic challenges in rapidly progressive dementia

INTRODUCTION

Rapidly progressive dementia is a syndrome caused by numerous disease entities. Accurate diagnosis is crucial as substantial proportion of these diseases is highly treatable. Others might implicate specific hygienic problems. Still, differential diagnosis remains challenging because of a huge overlap of clinical presentations. Areas covered: The paper reviews PubMed-listed research articles with a focus on diagnosis and treatment of diseases showing rapid cognitive decline such as inflammatory diseases, rapidly progressive neurodegenerative diseases, toxic-metabolic encephalopathies and prion diseases. The literature was interpreted in the light of experience in clinically differentiating rapid progressing dementia in the framework of Creutzfeldt-Jakob-Disease (CJD) surveillance activities. An overview of relevant differential diagnoses and diagnostic pitfalls as well as therapeutic protocols is presented. Expert commentary: Over the last years, more and more neurologic disorders causing cognitive symptoms, in particular various types of immune-mediated diseases have been discovered. To identify treatable conditions and to enhance knowledge of differential diagnosis and epidemiology, we suggest an extended diagnostic work up in cases with rapidly progressing dementia. Besides standard methods, this should include the search for neoplasia as well as atypical encephalitis. High-dose steroid therapy should be considered in certain clinical situations even when no evidence for inflammation is present.

Rapidly Progressive Dementia: Prevalence and Causes in a Neurologic Unit of a Tertiary Hospital in Brazil

BACKGROUND

Rapidly progressive dementia (RPD) is usually associated with Creutzfeldt-Jakob disease, a fatal condition. Current advances in the understanding of immune-mediated diseases allow the diagnosis of previously unrecognized treatable RPDs.

OBJECTIVE OF THE STUDY

The objective of the study was to describe the prevalence and causes of RPD in a neurology service, identifying potentially reversible causes.

METHODS

We carried out a cross-sectional evaluation of all patients admitted to the neurology unit of a tertiary hospital in Brazil between March 2012 and February 2015. We included patients who had progressed to moderate or severe dementia within a few months or up to 2 years at the time of hospitalization, and used multivariable logistic regression analysis to identify factors associated with a favorable outcome.

RESULTS

We identified 61 RPD (3.7%) cases among 1648 inpatients. Mean RPD patients' age was 48 years, and median time to progression was 6.4 months. Immune-mediated diseases represented the most commonly observed disease group in this series (45.9% of cases). Creutzfeldt-Jakob disease (11.5%) and nonprion neurodegenerative diseases (8.2%) were less common in this series. Outcome was favorable in 36/61 (59.0%) RPD cases and in 28/31 (89.3%) of immune-mediated cases. Favorable outcome was associated with shorter time from symptom onset to diagnosis and abnormal cerebrospinal fluid findings.

CONCLUSIONS

Immune-mediated diseases were the most common cause of RPD in this series. Timely evaluation and diagnosis along with institution of appropriate therapy are required in RPD, especially in view of potentially reversible causes.

The frequency of yeast [PSI+] prion formation is increased during chronological ageing

Ageing involves a time-dependent decline in a variety of intracellular mechanisms and is associated with cellular senescence. This can be exacerbated by prion diseases which can occur in a sporadic manner, predominantly during the later stages of life. Prions are infectious, self-templating proteins responsible for several neurodegenerative diseases in mammals and several prion-forming proteins have been found in yeast. We show here that the frequency of formation of the yeast [PSI⁺ ] prion, which is the altered form of the Sup35 translation termination factor, is increased during chronological ageing. This increase is exacerbated in an atg1 mutant suggesting that autophagy normally acts to suppress age-related prion formation. We further show that cells which have switched to [PSI⁺ ] have improved viability during chronological ageing which requires active autophagy. [PSI⁺ ] stains show increased autophagic flux which correlates with increased viability and decreased levels of cellular protein aggregation. Taken together, our data indicate that the frequency of [PSI⁺ ] prion formation increases during yeast chronological ageing, and switching to the [PSI⁺ ] form can exert beneficial effects via the promotion of autophagic flux.

Doxycycline in early CJD: a double-blinded randomised phase II and observational study

OBJECTIVES

The main objective of the present study is to study the therapeutic efficiency of doxycycline in a double-blinded randomised phase II study in a cohort of patients with sporadic Creutzfeldt-Jakob disease (sCJD).

METHODS

From the National Reference Center of TSE Surveillance in Germany, patients with probable or definite sCJD were recruited for a double-blinded randomised study with oral doxycycline (EudraCT 2006-003934-14). In addition, we analysed the data from patients with CJD who received compassionate treatment with doxycycline in a separate group. Potential factors which influence survival such as age at onset, gender, codon 129 polymorphism and cognitive functions were evaluated. The primary outcome measure was survival.

RESULTS

Group 1: in the double-blinded randomised phase II study, 7 patients in the treatment group were compared with 5 controls. Group 2: 55 patients with sCJD treated with oral doxycycline were analysed and compared with 33 controls by a stratified propensity score applied to a Cox proportional hazard analysis. The results of both studies were combined by means of a random-effects meta-analysis. A slight increase in survival time in the doxycycline treatment group was observed (p=0.049, HR=0.63 (95% CI 0.402 to 0.999)).

CONCLUSIONS

On the basis of our studies, a larger trial of doxycycline should be performed in persons in the earliest stages of CJD.

TRIAL REGISTRATION NUMBER

EudraCT 2006-003934-14; Results.

Prions: Beyond a Single Protein

Since the term protein was first coined in 1838 and protein was discovered to be the essential component of fibrin and albumin, all cellular proteins were presumed to play beneficial roles in plants and mammals. However, in 1967, Griffith proposed that proteins could be infectious pathogens and postulated their involvement in scrapie, a universally fatal transmissible spongiform encephalopathy in goats and sheep. Nevertheless, this novel hypothesis had not been evidenced until 1982, when Prusiner and coworkers purified infectious particles from scrapie-infected hamster brains and demonstrated that they consisted of a specific protein that he called a "prion." Unprecedentedly, the infectious prion pathogen is actually derived from its endogenous cellular form in the central nervous system. Unlike other infectious agents, such as bacteria, viruses, and fungi, prions do not contain genetic materials such as DNA or RNA. The unique traits and genetic information of prions are believed to be encoded within the conformational structure and posttranslational modifications of the proteins. Remarkably, prion-like behavior has been recently observed in other cellular proteins-not only in pathogenic roles but also serving physiological functions. The significance of these fascinating developments in prion biology is far beyond the scope of a single cellular protein and its related disease.

Antiprion Activity of DB772 and Related Monothiophene- and Furan-Based Analogs in a Persistently Infected Ovine Microglia Culture System

The transmissible spongiform encephalopathies are fatal neurodegenerative disorders characterized by the misfolding of the native cellular prion protein (PrP^C) into the accumulating, disease-associated isoform (PrP^Sc). Despite extensive research into the inhibition of prion accumulation, no effective treatment exists. Previously, we demonstrated the inhibitory activity of DB772, a monocationic phenyl-furan-benzimidazole, against PrP^Sc accumulation in sheep microglial cells. In an effort to determine the effect of structural substitutions on the antiprion activity of DB772, we employed an in vitro strategy to survey a library of structurally related, monothiophene- and furan-based compounds for improved inhibitory activity. Eighty-nine compounds were screened at 1 μM for effects on cell viability and prion accumulation in a persistently infected ovine microglia culture system. Eleven compounds with activity equivalent to or higher than that of DB772 were identified as preliminary hit compounds. For the preliminary hits, cytotoxicities and antiprion activities were compared to calculate the tissue culture selectivity index. A structure-activity relationship (SAR) analysis was performed to determine molecular components contributing to antiprion activity. To investigate potential mechanisms of inhibition, effects on PrP^C and PrP^Sc were examined. While inhibition of total PrP^C was not observed, the results suggest that a potential target for inhibition at biologically relevant concentrations is through PrP^C misfolding to PrP^Sc. Further, SAR analysis suggests that two structural elements were associated with micromolar antiprion activity. Taken together, the described data provide a foundation for deeper investigation into untested DB compounds and in the design of effective therapeutics.

Caregiver burden in atypical dementias: comparing frontotemporal dementia, Creutzfeldt-Jakob disease, and Alzheimer's disease

BACKGROUND

Caregiver burden is a significant issue in the treatment of dementia and a known contributor to institutionalization of patients with dementia. Published data have documented increased caregiver burden in behavioral variant frontotemporal dementia (bvFTD) compared to Alzheimer's disease (AD). Another atypical dementia with high-perceived caregiver burden is sporadic Creutzfeldt-Jakob disease (sCJD), but no formal studies have assessed this perception. The aim of this study was to compare caregiver burden across atypical dementia etiologies.

METHODS

76 adults with atypical dementia (young-onset AD [YOAD], bvFTD, language variant FTD [lvFTD], and sCJD) were administered an abbreviated version of the Zarit Burden Interview (ZBI), Neuropsychiatric Inventory (NPI-Q), and other assessment instruments during a five-year time period at Johns Hopkins Hospital (JHH). A Cox regression model examined differences between disease categories that impact mean ZBI scores.

RESULTS

Mean ZBI scores were significantly different between dementia etiologies, with bvFTD and sCJD having the highest caregiver burden (p = 0.026). Mean NPI-Q caregiver distress scores were highest in bvFTD and sCJD (p = 0.002), with sCJD and bvFTD also having the highest number of endorsed symptom domains (p = 0.012). On regression analyses, an interactive variable combining final diagnosis category and NPI-Q total severity score demonstrated statistically significant differences in mean ZBI scores for sCJD and bvFTD.

CONCLUSIONS

This study demonstrates that bvFTD and sCJD have increased levels of caregiver burden, NPI-Q caregiver distress, total severity scores, and number of endorsed symptom domains. These results suggest that higher caregiver burden in bvFTD and sCJD are disease specific and possibly related to neuropsychiatric symptoms.

Young-onset dementia epidemiology applied to neuropsychiatry practice

A substantial number of adults suffer young-onset dementia (YOD). The diversity of types and syndromes makes recognition and diagnosis difficult. An algorithmic approach to interpreting clinical data, informed by clinical epidemiology, integrates data pertaining to defining syndromes and their chronology and tempo, family history, and other neuropsychiatric features and neurologic signs, is used to reach a preliminary diagnosis and direct diagnostic tests and their interpretation. Screening for YOD in the psychiatric context is a rational process in which vigilance is combined with careful searches for red flags that signal a neurodegenerative etiology.

Lymphomatosis cerebri mimicking iatrogenic Creutzfeldt-Jakob disease

Lymphomatosis cerebri (LC) is a rare variant of primary central nervous system lymphoma (PCNSL) whereby individual lymphoma cells infiltrate the cerebral white matter without causing a mass effect. The disease characteristically presents as a rapidly progressive dementia, which opens an ample differential diagnosis of toxic, metabolic, neurodegenerative and infective causes. Other presentations also include changes in personality, myoclonus and psychotic symptoms. Here we report a patient who presented with a rapidly progressive dementia with a unique surgical history of a dural mater graft in the 1970s. The diagnosis of iatrogenic Creutzfeldt-Jakob disease (iCJD) was initially considered. However, the patient's clinical status deteriorated rapidly with no response to symptomatic treatment and she died 2 months after symptom onset. A diagnosis of T-type LC was reached at autopsy.

Prionic diseases

Prion diseases are neurodegenerative illnesses due to the accumulation of small infectious pathogens containing protein but apparently lacking nucleic acid, which have long incubation periods and progress inexorably once clinical symptoms appear. Prions are uniquely resistant to a number of normal decontaminating procedures. The prionopathies [Kuru, Creutzfeldt-Jakob disease (CJD) and its variants, Gerstmann-Sträussler-Scheinker (GSS) syndrome and fatal familial insomnia (FFI)] result from accumulation of abnormal isoforms of the prion protein in the brains of normal animals on both neuronal and non-neuronal cells. The accumulation of this protein or fragments of it in neurons leads to apoptosis and cell death. There is a strong link between mutations in the gene encoding the normal prion protein in humans (PRNP) - located on the short arm of chromosome 20 - and forms of prion disease with a familial predisposition (familial CJD, GSS, FFI). Clinically a prionopathy should be suspected in any case of a fast progressing dementia with ataxia, myoclonus, or in individuals with pathological insomnia associated with dysautonomia. Magnetic resonance imaging, identification of the 14-3-3 protein in the cerebrospinal fluid, tonsil biopsy and genetic studies have been used for in vivo diagnosis circumventing the need of brain biopsy. Histopathology, however, remains the only conclusive method to reach a confident diagnosis. Unfortunately, despite numerous treatment efforts, prionopathies remain short-lasting and fatal diseases.

Therapies for human prion diseases

The pathological foundation of human prion diseases is a result of the conversion of the physiological form of prion protein (PrP(c)) to the pathological protease resistance form PrP(res). Most patients with prion disease have unknown reasons for this conversion and the subsequent development of a devastating neurodegenerative disorder. The conversion of PrP(c) to PrP(res), with resultant propagation and accumulation results in neuronal death and amyloidogenesis. However, with increasing understanding of neurodegenerative processes it appears that protein-misfolding and subsequent propagation of these rouge proteins, is a generic phenomenon shared with diseases caused by tau, α-synucleins and β-amyloid proteins. Consequently, effective anti-prion agents may have wider implications. A number of therapeutic approaches include polyanionic, polycyclic drugs such as pentosan polysulfate (PPS), which prevent the conversion of PrP(c) to PrP(res) and might also sequester and down-regulate PrP(res). Polyanionic compounds might also help to clear PrP(res). Treatments aimed at the laminin receptor, which is an important accessory molecule in the conversion of PrP(c) to PrP(res) - neuroprotection, immunotherapy, siRNA and antisense approaches have provided some experimental promise.

The sleep-immunity relationship

Research models show a strong interrelationship between sleep quality and immune function. The proinflammatory cytokines, interleukin-1, interleukin-6, and tumor necrosis factor α are classified as official sleep-regulatory substances. However, sleep-promoting properties are also possessed by several other immune and proinflammatory cellular classes. This article reviews the current physiologic evidence for the prominent somnogenic and sleep-regulatory properties inherent to these immune substances. Clinical examples of this relationship are discussed from the perspective of infectious and primarily immune-related conditions associated with significant sleep disruption and from the perspective of immune dysregulation associated with several primary sleep disorders.

Unexpected frequent hepatotoxicity of a prescription drug, flupirtine, marketed for about 30 years

AIMS

To determine efficacy of the analgesic flupirtine in the treatment of overactive bladder syndrome in a proof-of-concept study.

METHODS

Double-blind, double-dummy, three-armed comparison of flupirtine extended release (400 mg/day, titrated to 600 mg/day), tolterodine extended release (4 mg/day) and placebo for 12 weeks.

RESULTS

When major elevations of liver enzymes (more than three times the upper normal limit) were detected in several flupirtine-exposed patients, the study was prematurely discontinued. Based on study-end data, hepatotoxicity was detected in 31% of patients receiving flupirtine for ≥ 6 weeks.

CONCLUSIONS

Unexpected frequent and relevant toxicity can occur when testing an established drug for a new indication.

Evidence for inhibitory effects of flupirtine, a centrally acting analgesic, on delayed rectifier k(+) currents in motor neuron-like cells

Flupirtine (Flu), a triaminopyridine derivative, is a centrally acting, non-opiate analgesic agent. In this study, effects of Flu on K⁺ currents were explored in two types of motor neuron-like cells. Cell exposure to Flu decreased the amplitude of delayed rectifier K⁺ current (I_K(DR)) with a concomitant raise in current inactivation in NSC-34 neuronal cells. The dissociation constant for Flu-mediated increase of I_K(DR) inactivation rate was about 9.8 μM. Neither linopirdine (10 μM), NMDA (30 μM), nor gabazine (10 μM) reversed Flu-induced changes in I_K(DR) inactivation. Addition of Flu shifted the inactivation curve of I_K(DR) to a hyperpolarized potential. Cumulative inactivation for I_K(DR) was elevated in the presence of this compound. Flu increased the amplitude of M-type K⁺ current (I_K(M)) and produced a leftward shift in the activation curve of I_K(M). In another neuronal cells (NG108-15), Flu reduced I_K(DR) amplitude and enhanced the inactivation rate of I_K(DR). The results suggest that Flu acts as an open-channel blocker of delayed-rectifier K⁺ channels in motor neurons. Flu-induced block of I_K(DR) is unlinked to binding to NMDA or GABA receptors and the effects of this agent on K⁺ channels are not limited to its action on M-type K⁺ channels.

Polythiophenes inhibit prion propagation by stabilizing prion protein (PrP) aggregates

Luminescent conjugated polymers (LCPs) interact with ordered protein aggregates and sensitively detect amyloids of many different proteins, suggesting that they may possess antiprion properties. Here, we show that a variety of anionic, cationic, and zwitterionic LCPs reduced the infectivity of prion-containing brain homogenates and of prion-infected cerebellar organotypic cultured slices and decreased the amount of scrapie isoform of PrP(C) (PrP(Sc)) oligomers that could be captured in an avidity assay. Paradoxically, treatment enhanced the resistance of PrP(Sc) to proteolysis, triggered the compaction, and enhanced the resistance to proteolysis of recombinant mouse PrP(23-231) fibers. These results suggest that LCPs act as antiprion agents by transitioning PrP aggregates into structures with reduced frangibility. Moreover, ELISA on cerebellar organotypic cultured slices and in vitro conversion assays with mouse PrP(23-231) indicated that poly(thiophene-3-acetic acid) may additionally interfere with the generation of PrP(Sc) by stabilizing the conformation of PrP(C) or of a transition intermediate. Therefore, LCPs represent a novel class of antiprion agents whose mode of action appears to rely on hyperstabilization, rather than destabilization, of PrP(Sc) deposits.