Major Dementia Syndromes Research Articles

Comprehension of acoustically degraded speech in Alzheimer's disease and primary progressive aphasia.

Successful communication in daily life depends on accurate decoding of speech signals that are acoustically degraded by challenging listening conditions. This process presents the brain with a demanding computational task that is vulnerable to neurodegenerative pathologies. However, despite recent intense interest in the link between hearing impairment and dementia, comprehension of acoustically degraded speech in these diseases has been little studied. Here we addressed this issue in a cohort of 19 patients with typical Alzheimer's disease and 30 patients representing the three canonical syndromes of primary progressive aphasia (non-fluent/agrammatic variant primary progressive aphasia; semantic variant primary progressive aphasia; logopenic variant primary progressive aphasia), compared to 25 healthy age-matched controls. As a paradigm for the acoustically degraded speech signals of daily life, we used noise-vocoding: synthetic division of the speech signal into frequency channels constituted from amplitude-modulated white noise, such that fewer channels convey less spectrotemporal detail thereby reducing intelligibility. We investigated the impact of noise-vocoding on recognition of spoken three-digit numbers and used psychometric modelling to ascertain the threshold number of noise-vocoding channels required for 50% intelligibility by each participant. Associations of noise-vocoded speech intelligibility threshold with general demographic, clinical and neuropsychological characteristics and regional grey matter volume (defined by voxel-based morphometry of patients' brain images) were also assessed. Mean noise-vocoded speech intelligibility threshold was significantly higher in all patient groups than healthy controls, and significantly higher in Alzheimer's disease and logopenic variant primary progressive aphasia than semantic variant primary progressive aphasia (all P < 0.05). In a receiver operating characteristic analysis, vocoded intelligibility threshold discriminated Alzheimer's disease, non-fluent variant and logopenic variant primary progressive aphasia patients very well from healthy controls. Further, this central hearing measure correlated with overall disease severity but not with peripheral hearing or clear speech perception. Neuroanatomically, after correcting for multiple voxel-wise comparisons in predefined regions of interest, impaired noise-vocoded speech comprehension across syndromes was significantly associated (P < 0.05) with atrophy of left planum temporale, angular gyrus and anterior cingulate gyrus: a cortical network that has previously been widely implicated in processing degraded speech signals. Our findings suggest that the comprehension of acoustically altered speech captures an auditory brain process relevant to daily hearing and communication in major dementia syndromes, with novel diagnostic and therapeutic implications.

FDG-PET Imaging of Dementia and Neurodegenerative Disease

Dementia syndromes present a diagnostic challenge given their overlapping clinical features and insidious presentations. Cerebral 2-deoxy-2-[F-18]fluoroglucose (FDG) positron emission tomography (PET) is a functional imaging modality commonly used in the evaluation of dementia. While its role in the clinical assessment of dementia is evolving, FDG PET allows for qualitative and quantitative characterization of major dementia syndromes and variants by means of detecting distinct patterns of cortical hypometabolism. Familiarity with these "metabolic signatures" in dementia syndromes can be helpful when interpreting cerebral FDG PET.

Altered Time Awareness in Dementia.

Our awareness of time, specifically of longer intervals spanning hours, days, months, and years, is critical for ensuring our sense of self-continuity. Disrupted time awareness over such intervals is a clinical feature in a number of frontotemporal dementia syndromes and Alzheimer's disease, but has not been studied and compared systematically in these diseases. We used a semi-structured caregiver survey to capture time-related behavioral alterations in 71 patients representing all major sporadic and genetic syndromes of frontotemporal dementia, in comparison to 28 patients with typical Alzheimer's disease and nine with logopenic aphasia, and 32 healthy older individuals. Survey items pertained to apparent difficulties ordering past personal events or estimating time intervals between events, temporal rigidity and clockwatching, and propensity to relive past events. We used a logistic regression model including diagnosis, age, gender, and disease severity as regressors to compare the proportions of individuals exhibiting each temporal awareness symptom between diagnostic groups. Gray matter associations of altered time awareness were assessed using voxel-based morphometry. All patient groups were significantly more prone to exhibit temporal awareness symptoms than healthy older individuals. Clinical syndromic signatures were identified. While patients with typical and logopenic Alzheimer's disease most frequently exhibited disturbed event ordering or interval estimation, patients with semantic dementia were most prone to temporal rigidity and clockwatching and those with behavioral variant frontotemporal dementia commonly exhibited all these temporal symptoms as well as a propensity to relive past events. On voxel-based morphometry, the tendency to relive past events was associated with relative preservation of a distributed left-sided temporo-parietal gray matter network including hippocampus. These findings reveal a rich and complex picture of disturbed temporal awareness in major dementia syndromes, with stratification of frontotemporal dementia syndromes from Alzheimer's disease. This is the first study to assess symptoms of altered temporal awareness across frontotemporal dementia syndromes and provides a motivation for future work directed to the development of validated clinical questionnaires, analysis of underlying neurobiological mechanisms and design of interventions.

Excessive Daytime Sleepiness in Major Dementia Syndromes.

There has been no comparison of excessive daytime sleepiness (EDS) in patients with Alzheimer's disease dementia (AD), dementia with Lewy bodies (DLB), and behavioral variant frontotemporal dementia (bvFTD). We identified patients with mild dementia who met criteria for these disorders who also had the Epworth Sleepiness Scale (ESS) completed. The sample included 17 bvFTD, 111 AD, and 31 DLB. An ESS score ≥10 was considered abnormal and consistent with EDS. Analyses with age and sex as covariates revealed higher mean ESS scores for DLB compared to the other groups (DLB 13.9 [5], bvFTD 9.6 [8], AD 8.8 [5], P < .05). An ESS score ≥10 was significantly more likely to occur in DLB compared to bvFTD or AD (DLB 81% vs bvFTD 47% vs AD 45%, P < .01). In patients with mild dementia, EDS is greatest in DLB and comparably lower in bvFTD and AD.

Music Perception in Dementia.

Despite much recent interest in music and dementia, music perception has not been widely studied across dementia syndromes using an information processing approach. Here we addressed this issue in a cohort of 30 patients representing major dementia syndromes of typical Alzheimer's disease (AD, n = 16), logopenic aphasia (LPA, an Alzheimer variant syndrome; n = 5), and progressive nonfluent aphasia (PNFA; n = 9) in relation to 19 healthy age-matched individuals. We designed a novel neuropsychological battery to assess perception of musical patterns in the dimensions of pitch and temporal information (requiring detection of notes that deviated from the established pattern based on local or global sequence features) and musical scene analysis (requiring detection of a familiar tune within polyphonic harmony). Performance on these tests was referenced to generic auditory (timbral) deviance detection and recognition of familiar tunes and adjusted for general auditory working memory performance. Relative to healthy controls, patients with AD and LPA had group-level deficits of global pitch (melody contour) processing while patients with PNFA as a group had deficits of local (interval) as well as global pitch processing. There was substantial individual variation within syndromic groups. Taking working memory performance into account, no specific deficits of musical temporal processing, timbre processing, musical scene analysis, or tune recognition were identified. The findings suggest that particular aspects of music perception such as pitch pattern analysis may open a window on the processing of information streams in major dementia syndromes. The potential selectivity of musical deficits for particular dementia syndromes and particular dimensions of processing warrants further systematic investigation.

Distinguishing Alzheimer’s disease from other major forms of dementia

Alzheimer’s disease (AD) is the most common and most studied cause of dementia. Significant advances have been made since the first set of clinical criteria for AD were put forth in 1984 that are now captured in the new criteria for AD published in 2011. Key features include recognition of a broad AD spectrum (from preclinical to mild cognitive impairment to AD dementia) and requirement of AD biomarkers for diagnosis. Correctly diagnosing dementia type is increasingly important in an era when potential disease-modifying agents are soon to be marketed. The typical AD dementia syndrome has at its core, an amnestic syndrome of the hippocampal type, followed by associated deficits in word-finding, spatial cognition, executive functions and neuropsychiatric changes. Atypical presentations of AD have also been identified that are presumed to have a different disease course. It can be difficult to distinguish between the various dementia syndromes given the overlap in many common clinical features across the dementias. The clinical difficulty in diagnosis may reflect the underlying pathology, as AD often co-occurs with other pathologies at autopsy, such as cerebrovascular disease or Lewy bodies. Neuropsychological evaluation has provided clinicians and researchers with profiles of cognitive strengths and weaknesses that help to define the dementias. There is yet no single behavioral marker that can reliably discriminate AD from the other dementias. The combined investigation of cognitive and neurobehavioral symptoms coupled with imaging markers could provide a more accurate approach for differentiating between AD and other major dementia syndromes in the future.

Functional Neuroimaging in Dementia and other Amnesic Disorders: A Radiological Review

Problem statement: The structural and functional neuroimaging have much to contribute to the cognitive neuroscience. Approach: We describe a radiological review of the major dementia syndromes and Mild Cognitive Impairment (MCI), included Alzheimer's disease, Lewy body dementia, Vascular dementia, Front temporal Lobar degeneration, Dementia associated with parkinsonism and other amnesic syndromes. Results: The different syndromes and diseases presenting with dementia have different patterns of brain perfusion abnormalities, it is possible to distinguish them with good specificity with neuroimaging. Conclusion: New imaging techniques carry the hope of revolutionizing the diagnosis of dementia so as to obtain a complete molecular, structural and metabolic characterization, which could be used to improve diagnosis and to stage each patient and follow disease progression and response to treatment. Structural and functional imaging modalities contribute to the diagnosis and understanding of the different dementias.

Dementia with Lewy bodies.

An increasing variety of neurological syndromes and brain disorders have been associated with Lewy body pathology in various parts of the nervous system’. The major dementia syndromes in which Lewy bodies are frequently identified are Dementia with Lewy bodies (DLB), dementia arising in Parkinson’s disease, and Alzheimer’s disease. Within each of these clinico-pathological umbrellas many patients can be allocated to the core syndromes based on a combination of clinical features and the pathological changes demonstrable at autopsy. However, there is a substantial, and currently unquantified, overlap between them such that some authors have proposed a continuum of Lewy body and Alzheimer-type pathologies2. The paradigms of Parkinson’s disease and Alzheimer’s disease have been absorbed into clinical practice, pathological interpretation at autopsy, and models of pathogenesis, to such an extent that DLB has been difficult to assimilate. DLB is currently defined in terms of a clinical syndrome and prospective pathological studies suggest that this syndrome predicts the presence of Lewy body pathology at least as well as a diagnosis of AD can predict the pathology of that disorder3. Similar considerations apply to Parkinson’s disease so that for each of the three syndromes the currently accepted clinical criteria for their diagnosis is likely to be verified at autopsy in at least 4 out of 5 cases. The clinical features of DLB are defined in the published consensus criteria from an International Workshop held in 19954. Many studies published subsequently have turned the concept of DLBKeywordsLewy BodyDementia With Lewy BodyLewy Body DiseaseLewy Body DementiaDementia With Lewy Body PatientThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.