Nuclear imaging can predict pathologic diagnosis in progressive nonfluent aphasia

Jargonaphasia in logopenic variant primary progressive aphasia

BACKGROUND

Logopenic variant primary progressive aphasia (lvPPA), which is most commonly an early onset variant of Alzheimer's disease (AD), is a progressive impairment in word retrieval and language expression. Clinicians often misdiagnose these patients when they present with severely unintelligible speech consistent with jargonaphasia.

METHODS

We reviewed all patients presenting to a behavioral neurology program over a 23-year period who met criteria for lvPPA after completion of an evaluation extending to positron emission tomography (PET) of the brain. Among these lvPPA patients, we additionally identified and characterized those whose presentation involved incomprehensible yet fluent verbal output.

RESULTS

Out of 95 patients with lvPPA, 9 (9.47%) had jargonaphasia on presentation. These patients differed from the remaining 86 patients in lacking awareness or concern for their impaired communication, having worse mental status scale scores, greater auditory comprehension difficulty, and more bilateral temporo-parietal hypometabolism. In addition, 44.4% of those with jargonaphasia, compared to 14% of those without, were bi/multilingual.

CONCLUSION

Nearly 1 in 10 patients with lvPPA present with severely unintelligible speech. These patients have disease extending to bilateral temporoparietal areas affecting language comprehension and disease awareness. Jargonaphasia can be a confusing presentation of AD and must be differentiated from other progressive aphasias, Wernicke's aphasia, and the word salad of "schizoaphasia".

Brain total creatine differs between primary progressive aphasia (PPA) subtypes and correlates with disease severity

Primary progressive aphasia (PPA) is comprised of three subtypes: logopenic (lvPPA), non-fluent (nfvPPA), and semantic (svPPA). We used magnetic resonance spectroscopy (MRS) to measure tissue-corrected metabolite levels in the left inferior frontal gyrus (IFG) and right sensorimotor cortex (SMC) from 61 PPA patients. We aimed to: (1) characterize subtype differences in metabolites; and (2) test for metabolite associations with symptom severity. tCr differed by subtype across the left IFG and right SMC. tCr levels were lowest in lvPPA and highest in svPPA. tCr levels predicted lvPPA versus svPPA diagnosis. Higher IFG tCr and lower Glx correlated with greater disease severity. As tCr is involved in brain energy metabolism, svPPA pathology might involve changes in specific cellular energy processes. Perturbations to cellular energy homeostasis in language areas may contribute to symptoms. Reduced cortical excitatory capacity (i.e. lower Glx) in language regions may also contribute to symptoms. Thus, tCr may be useful for differentiating between PPA subtypes, and both tCr and Glx might have utility in understanding PPA mechanisms and tracking progression.

Noninvasive Brain Stimulation in Primary Progressive Aphasia: A Literature Review

Primary progressive aphasia (PPA) is a gradually progressive clinical syndrome in which the first and predominant symptoms involve language and/or speech production that interfere with daily activities. Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) appear to have a beneficial impact on many neurodegenerative pathologies. The current review investigated the impact of rTMS and tDCS on PPA patients. English language articles that have been published in the databases PubMed, and Scopus from 2007 to 2022 were included. Fifteen single-case or small-group studies were analyzed and presented. The majority of the literature findings point toward that the application of rTMS or tDCS may have a positive effect in improving symptoms such as verb production, action naming, phonemic-verbal fluency, grammatical comprehension, written spelling, and semantic features. In conclusion, our review provides additional evidence supporting that both types of stimulation may improve linguistic deficits, especially if they combined, speech therapy.

Validity of cingulate–precuneus–temporo-parietal hypometabolism for single-subject diagnosis of biomarker-proven atypical variants of Alzheimer’s Disease

The aim of our study was to establish empirically to what extent reduced glucose uptake in the precuneus, posterior cingulate and/or temporo-parietal cortex (PCTP), which is thought to indicate brain amyloidosis in patients with dementia or MCI due to Alzheimer’s Disease (AD), permits to distinguish amyloid-positive from amyloid-negative patients with non-classical AD phenotypes at the single-case level. We enrolled 127 neurodegenerative patients with cognitive impairment and a positive (n. 63) or negative (n. 64) amyloid marker (cerebrospinal fluid or amy-PET). Three rating methods of FDG-PET scan were applied: purely qualitative visual interpretation of uptake images (VIUI), and visual reading assisted by a semi-automated and semi-quantitative tool: INLAB, provided by the Italian National Research Council, or Cortex ID Suite, marketed by GE Healthcare. Fourteen scans (11.0%) patients remained unclassified by VIUI or INLAB procedures, therefore, validity values were computed on the remaining 113 cases. The three rating approaches showed good total accuracy (77–78%), good to optimal sensitivity (81–93%), but poorer specificity (62–75%). VIUI showed the highest sensitivity and the lowest specificity, and also the highest proportion of unclassified cases. Cases with asymmetric temporo-parietal hypometabolism and a progressive aphasia or corticobasal clinical profile, in particular, tended to be rated as AD-like, even if biomarkers indicated non-amyloid pathology. Our findings provide formal support to the value of PCTP hypometabolism for single-level diagnosis of amyloid pathophysiology in atypical AD, but also highlight the risk of qualitative assessment to misclassify patients with non-AD PPA or CBS underpinned by asymmetric temporo-parietal hypometabolism.

Noninvasive brain stimulation to augment language therapy for primary progressive aphasia

Primary progressive aphasia (PPA) is a debilitating disorder characterized by the gradual loss of language functioning resulting from neurodegenerative diseases including frontotemporal lobar degeneration or Alzheimer's disease pathology. There is a dearth of research investigating language therapy in PPA. Unlike individuals with poststroke aphasia, language skills are expected to decline over time, so the goal of treatment is often to preserve existing language functioning. There has been an increasing interest in using non-invasive brain stimulation including transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) to augment traditional behavioral therapy in PPA. Research is promising and suggests neuromodulation can lead to generalization and maintenance of treatment effects for a longer period compared to behavioral therapy alone. Emerging research is also beginning to identify predictors of treatment response. Yet there is still much to learn regarding how neuromodulation factors (e.g., type of stimulation, stimulation intensity), participant factors (e.g., demographics, extent and location of atrophy), and treatment factors (e.g., type of language therapy, and dosage) will interact to predict treatment response. We are moving toward a promising future where individuals with PPA will benefit from individualized therapy protocols pairing traditional language therapy with neuromodulation.

EANM procedure guidelines for brain PET imaging using [18F]FDG, version 3

The present procedural guidelines summarize the current views of the EANM Neuro-Imaging Committee (NIC). The purpose of these guidelines is to assist nuclear medicine practitioners in making recommendations, performing, interpreting, and reporting results of [¹⁸F]FDG-PET imaging of the brain. The aim is to help achieve a high-quality standard of [¹⁸F]FDG brain imaging and to further increase the diagnostic impact of this technique in neurological, neurosurgical, and psychiatric practice. The present document replaces a former version of the guidelines that have been published in 2009. These new guidelines include an update in the light of advances in PET technology such as the introduction of digital PET and hybrid PET/MR systems, advances in individual PET semiquantitative analysis, and current broadening clinical indications (e.g., for encephalitis and brain lymphoma). Further insight has also become available about hyperglycemia effects in patients who undergo brain [¹⁸F]FDG-PET. Accordingly, the patient preparation procedure has been updated. Finally, most typical brain patterns of metabolic changes are summarized for neurodegenerative diseases. The present guidelines are specifically intended to present information related to the European practice. The information provided should be taken in the context of local conditions and regulations.

Qualitative and Quantitative Analyses of Brain 18Fluoro-Deoxy-Glucose Positron Emission Tomography in Primary Progressive Aphasia

BACKGROUND

A primary progressive aphasia (PPA) diagnosis is generally based on clinical criteria, but often symptoms and signs may overlap in the different forms. Recent data have evidenced that brain 18fluoro-deoxy-glucose positron emission tomography (18F-FDG PET) could support the clinical diagnosis, since specific metabolic patterns are described for the different variants.

AIMS

We further evaluated the usefulness of 18F-FDG PET, by both visual qualitative (QL) and quantitative (QN) methods in the initial diagnosis of PPA, focusing on the classification of different variants. Moreover, we also analyzed the role of 18F-FDG PET in clarifying the association of PPA with the early phase of Alzheimer's disease (AD) or frontotemporal (FTD) dementias.

METHODS

We consecutively enrolled 35 patients with clinical symptoms of aphasia, suspect of or attributable to PPA. Patients were classified into two groups: 18 cases with clinical symptoms of aphasia but normal neuropsychological tests and an unclear classification of a specific PPA variant (group A) and 17 cases with clinical and neuropsychological signs attributable to PPA with an uncertain differential diagnosis between AD and FTD (group B). All patients underwent brain 18F-FDG PET/CT, and images were evaluated both by QL and QN, the latter applying an automated analysis program that produced brain regional metabolicmaps and normal age-matched control group comparative analysis (zscore).

RESULTS

18F-FDG PET showed different patterns of bilateral cortical hypometabolism in the two groups. The combined use of QL and QN permitted to achieved a correct PPA variant diagnosis in 8 of 18 (44.4%) cases of group A and in 14 of 17 (82.3%) of group B, while only QN could support the correct classification of PPA variants in 10 of 18 (55.6%) cases of group A and in 3 of 17 (17.7%) cases of group B in whom the procedure better localized the hypometabolic areas.

CONCLUSIONS

Brain 18F-FDG PET had an elevated performance in the early diagnosis of PPA variants and in the advanced PPA AD/FTD classification. QL clarified the development of AD or FTD in advanced PPA cases and supported the differential diagnosis of a PPA variant in a few early cases. QN 18F-FDG PET evaluation better contributed to the early diagnosis of an unclear metabolic pattern. To correctly identify all cases, patients with diffuse cortical hypometabolism were also included. Larger series are necessary to confirm these data.

White Matter Damage in the Semantic Variant of Primary Progressive Aphasia

BACKGROUND

The semantic variant of primary progressive aphasia (svPPA) is a form of dementia, mainly featuring language impairment, for which the extent of white matter (WM) damage is less described than its associated grey matter (GM) atrophy. Our study aimed to characterise the extent of this damage using a sensitive and unbiased approach.

METHODS

We conducted a between-group study comparing 10 patients with a clinical diagnosis of svPPA, recruited between 2011 and 2014 at a tertiary reference centre, with 9 cognitively healthy, age-matched controls. From diffusion tensor imaging (DTI) data, we extracted fractional anisotropy (FA) values using a tract-based spatial statistics approach. We further obtained GM volumetric data using the Freesurfer automated segmentation tool. We compared both groups using non-parametric Wilcoxon rank-sum tests, correcting for multiple comparisons.

RESULTS

Demographic data showed that patients and controls were comparable. As expected, clinical data showed lower results in svPPA than controls on cognitive screening tests. Tractography showed impaired diffusion in svPPA patients, with FA mostly decreased in the longitudinal, uncinate, cingulum and external capsule fasciculi. Volumetric data show significant atrophy in svPPA patients, mostly in the left entorhinal, amygdala, inferior temporal, middle temporal, superior temporal and temporal pole cortices, and bilateral fusiform gyri.

CONCLUSIONS

This syndrome appears to be associated not only with GM but also significant WM degeneration. Thus, DTI could play a role in the differential diagnosis of atypical dementia by specifying WM damage specific to svPPA.

European Association of Nuclear Medicine and European Academy of Neurology recommendations for the use of brain 18 F-fluorodeoxyglucose positron emission tomography in neurodegenerative cognitive impairment and dementia: Delphi consensus

BACKGROUND AND PURPOSE

Recommendations for using fluorodeoxyglucose positron emission tomography (FDG-PET) to support the diagnosis of dementing neurodegenerative disorders are sparse and poorly structured.

METHODS

Twenty-one questions on diagnostic issues and on semi-automated analysis to assist visual reading were defined. Literature was reviewed to assess study design, risk of bias, inconsistency, imprecision, indirectness and effect size. Critical outcomes were sensitivity, specificity, accuracy, positive/negative predictive value, area under the receiver operating characteristic curve, and positive/negative likelihood ratio of FDG-PET in detecting the target conditions. Using the Delphi method, an expert panel voted for/against the use of FDG-PET based on published evidence and expert opinion.

RESULTS

Of the 1435 papers, 58 papers provided proper quantitative assessment of test performance. The panel agreed on recommending FDG-PET for 14 questions: diagnosing mild cognitive impairment due to Alzheimer's disease (AD), frontotemporal lobar degeneration (FTLD) or dementia with Lewy bodies (DLB); diagnosing atypical AD and pseudo-dementia; differentiating between AD and DLB, FTLD or vascular dementia, between DLB and FTLD, and between Parkinson's disease and progressive supranuclear palsy; suggesting underlying pathophysiology in corticobasal degeneration and progressive primary aphasia, and cortical dysfunction in Parkinson's disease; using semi-automated assessment to assist visual reading. Panellists did not support FDG-PET use for pre-clinical stages of neurodegenerative disorders, for amyotrophic lateral sclerosis and Huntington disease diagnoses, and for amyotrophic lateral sclerosis or Huntington-disease-related cognitive decline.

CONCLUSIONS

Despite limited formal evidence, panellists deemed FDG-PET useful in the early and differential diagnosis of the main neurodegenerative disorders, and semi-automated assessment helpful to assist visual reading. These decisions are proposed as interim recommendations.

Diagnostic utility of FDG-PET in the differential diagnosis between different forms of primary progressive aphasia

Purpose

A joint effort of the European Association of Nuclear Medicine (EANM) and the European Academy of Neurology (EAN) aims at clinical guidance for the use of FDG-PET in neurodegenerative diseases. This paper addresses the diagnostic utility of FDG-PET over clinical/neuropsychological assessment in the differentiation of the three forms of primary progressive aphasia (PPA).

Methods

Seven panelists were appointed by the EANM and EAN and a literature search was performed by using harmonized PICO (Population, Intervention, Comparison, Outcome) question keywords. The studies were screened for eligibility, and data extracted to assess their methodological quality. Critical outcomes were accuracy indices in differentiating different PPA clinical forms. Subsequently Delphi rounds were held with the extracted data and quality assessment to reach a consensus based on both literature and expert opinion.

Results

Critical outcomes for this PICO were available in four of the examined papers. The level of formal evidence supporting clinical utility of FDG-PET in differentiating among PPA variants was considered as poor. However, the consensual recommendation was defined on Delphi round I, with six out of seven panelists supporting clinical use.

Conclusions

Quantitative evidence demonstrating utility or lack thereof is still missing. Panelists decided consistently to provide interim support for clinical use based on the fact that a typical atrophy or metabolic pattern is needed for PPA according to the diagnostic criteria, and the synaptic failure detected by FDG-PET is an earlier phenomenon than atrophy. Also, a normal FDG-PET points to a non-neurodegenerative cause.

A Longitudinal Study of a Chinese Man Presenting with Non-Fluent/Agrammatic Variant of Primary Progressive Aphasia

Primary progressive aphasia (PPA) is a neurodegenerative disease characterized by declining language ability. However, the difficulty in defining the central clinical features in its earliest stage and establishing the dynamics of its progression has led to controversy. We report a 71-year-old man with Han language suffering from non-fluent/agrammatic variant of PPA but presenting as typical Alzheimer’s disease (AD) and confused with logopenic variant of PPA in its early stage, longitudinally describing his clinical characteristics, neuroanatomical basis, and genetic associations, and exploring the underlying pathology. This case highlights a longitudinal data for reliably discriminating among AD and PPA variants and helps to deepen our understanding of Han language non-fluent/agrammatic variant of PPA.

Autopsy as Gold Standard in FDG-PET Studies in Dementia

Positron emission tomography (PET) imaging with F18-fluorodeoxyglucose (FDG) is increasingly used as an adjunct to clinical evaluation in the diagnosis of dementia. Considering that most FDG-PET studies in dementia use clinical diagnosis as gold standard and that clinical diagnosis is approximately 80% sensitive or accurate, we aim to review the evidence-based data on the diagnostic accuracy of brain FDG-PET in dementia when cerebral autopsy is used as gold standard. We searched the PubMed and Medline databases for dementia-related articles that correlate histopathological diagnosis at autopsy with FDG-PET imaging and found 47 articles among which there were only 5 studies of 20 patients or more. We were able to conclude that sensitivity and specificity of FDG-PET for Alzheimer's disease are good, but more studies using histopathological diagnosis at autopsy as gold standard are needed in order to evaluate what FDG-PET truly adds to premortem diagnostic accuracy in dementia.

Biomarkers in the primary progressive aphasias

BACKGROUND

Primary progressive aphasia (PPA) is a progressive disorder of language that is increasingly recognised as an important presentation of a specific spectrum of neurodegenerative conditions.

AIMS

In an era of etiologically specific treatments for neurodegenerative conditions, it is crucial to establish the histopathologic basis for PPA. In this review, I discuss biomarkers for identifying the pathology underlying PPA.

MAIN CONTRIBUTION

Clinical syndromes suggest a probabilistic association between a specific PPA variant and an underlying pathology, but there are also many exceptions. A considerable body of work with biomarkers is now emerging as an important addition to clinical diagnosis. I review genetic, neuroimaging and biofluid studies that can help determine the pathologic basis for PPA.

CONCLUSIONS

Together with careful clinical examination, there is great promise that supplemental biomarker assessments will lead to accurate diagnosis of the pathology associated with PPA during life and serve as the basis for clinical trials in this spectrum of disease.

Agrammatic primary progressive aphasia in two dextral patients with right hemispheric involvement

Agrammatic primary progressive aphasia (PPA-G) has been known to be associated with focal brain atrophy involving the left posterior frontal and anterior insular regions. However, aphasia can also rarely result from right hemispheric lesions in right-handed patients, so-called crossed aphasia in dextrals (CAD). We report two right-handed patients with PPA-G whose 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) showed hypometabolism predominantly in the right hemisphere, implicating "crossed PPA-G."

Disruption of large-scale neural networks in non-fluent/agrammatic variant primary progressive aphasia associated with frontotemporal degeneration pathology

Non-fluent/agrammatic primary progressive aphasia (naPPA) is a progressive neurodegenerative condition most prominently associated with slowed, effortful speech. A clinical imaging marker of naPPA is disease centered in the left inferior frontal lobe. We used multimodal imaging to assess large-scale neural networks underlying effortful expression in 15 patients with sporadic naPPA due to frontotemporal lobar degeneration (FTLD) spectrum pathology. Effortful speech in these patients is related in part to impaired grammatical processing, and to phonologic speech errors. Gray matter (GM) imaging shows frontal and anterior-superior temporal atrophy, most prominently in the left hemisphere. Diffusion tensor imaging reveals reduced fractional anisotropy in several white matter (WM) tracts mediating projections between left frontal and other GM regions. Regression analyses suggest disruption of three large-scale GM-WM neural networks in naPPA that support fluent, grammatical expression. These findings emphasize the role of large-scale neural networks in language, and demonstrate associated language deficits in naPPA.

Neuroimaging and biochemical markers in the three variants of primary progressive aphasia

BACKGROUND/AIM

To investigate in variants of primary progressive aphasia (PPA) the association between current clinical and neuroimaging criteria and biochemical/genetic markers at the individual level.

METHODS

Thirty-two PPA patients were classified as non-fluent/agrammatic (nfvPPA), semantic (svPPA), or logopenic variant (lvPPA) or as unclassifiable (uPPA). In all patients, we evaluated the neuroimaging criteria (magnetic resonance imaging and/or single photon emission computed tomography/positron emission tomography) of each variant and studied serum progranulin levels, APOE genotype and Alzheimer's disease (AD)-cerebrospinal fluid (CSF) biomarkers. Cases with a first-degree family history of early-onset dementia were genetically tested.

RESULTS

Ten of 15 (66%) nfvPPA, 5/5 (100%) svPPA and 7/7 (100%) lvPPA patients showed at least one positive neuroimaging-supported diagnostic criterion. All lvPPA and 3/5 (60%) uPPA patients presented AD-CSF biomarkers, which were absent in nfvPPA and svPPA cases. Four (27%) nfvPPA patients had dementia-causing mutations: 2 carried a GRN mutation and 2 the C9ORF72 hexanucleotide expansion.

CONCLUSIONS

There was an excellent association between clinical criteria and neuroimaging-supported biomarkers in svPPA and lvPPA, as well as with AD-CSF biochemical markers in the lvPPA. Neuroimaging, biochemical and genetic findings in nfvPPA were heterogeneous. Incorporating biochemical/genetic markers into the PPA clinical diagnosis would allow clinicians to improve their predictions of PPA neuropathology, especially in nfvPPA and uPPA cases.

The non-fluent/agrammatic variant of primary progressive aphasia

The non-fluent/agrammatic variant of primary progressive aphasia (naPPA) is a young-onset neurodegenerative disorder characterised by poor grammatical comprehension and expression and a disorder of speech sound production. In an era of disease-modifying treatments, the identification of naPPA might be an important step in establishing a specific cause of neurodegenerative disease. However, difficulties in defining the characteristic language deficits and heterogeneity in the anatomical distribution of disease in naPPA have led to controversy. Findings from imaging studies have linked an impairment of this uniquely human language capacity with disruption of large-scale neural networks centred in left inferior frontal and anterior superior temporal regions. Accordingly, the pathological burden of disease in naPPA is anatomically focused in these regions. Most cases of naPPA are associated with the spectrum of pathological changes found in frontotemporal lobar degeneration involving the microtubule-associated protein tau. Knowledge of these unique clinical-pathological associations should advance care for patients with this important class of neurodegenerative diseases while supplementing our knowledge of human cognitive neuroscience.

Positive effects of language treatment for the logopenic variant of primary progressive aphasia

Despite considerable recent progress in understanding the underlying neurobiology of primary progressive aphasia (PPA) syndromes, relatively little attention has been directed toward the examination of behavioral interventions that may lessen the pervasive communication problems associated with PPA. In this study, we report on an individual with a behavioral profile and cortical atrophy pattern consistent with the logopenic variant of PPA. At roughly two-and-a-half years post onset, his marked lexical retrieval impairment prompted administration of a semantically based intervention to improve word retrieval. The treatment was designed to improve self-directed efforts to engage the participant's relatively preserved semantic system in order to facilitate word retrieval. His positive response to an intensive (2-week) dose of behavioral treatment was associated with improved lexical retrieval of items within trained categories, and generalized improvement for naming of untrained items that lasted over a 6-month follow-up interval. These findings support the potential value of intensive training to achieve self-directed strategic compensation for lexical retrieval difficulties in logopenic PPA. Additional insight was gained regarding the neural regions that supported improved performance by the administration of a functional magnetic resonance imaging protocol before and after treatment. In the context of a picture-naming task, post-treatment fMRI showed increased activation of left dorsolateral prefrontal regions that have been implicated in functional imaging studies of generative naming in healthy individuals. The increased activation in these frontal regions that were not significantly atrophic in our patient (as determined by voxel-based morphometry) is consistent with the notion that neural plasticity can support compensation for specific language loss, even in the context of progressive neuronal degeneration.

Biomarkers in frontotemporal lobar degeneration

PURPOSE OF REVIEW

Recent findings assessing the utility of neuroimaging and biofluid biomarkers are reviewed that help identify patients with frontotemporal lobar degeneration (FTLD) spectrum abnormality.

RECENT FINDINGS

Neuroimaging studies using T1 structural MRI and diffusion tensor imaging (DTI) distinguish between patients with FTLD and Alzheimer's disease, although the reliability of these group-level findings in individual patients has been assessed only rarely. However, innovative analyses such as support vector machine approaches are able to integrate T1 and DTI imaging results and to identify specific MRI profiles that distinguish between individual patients with FTLD and Alzheimer's disease. Novel radioligand positron emission tomography assessments also can recognize Alzheimer's disease patients with a clinical phenotype resembling that seen in FTLD. Biofluid studies identify about 15% of patients with FTLD due to a genetic mutation that is associated with the specific histopathologic features of TDP-43 or a tauopathy. Other genetically-based risk factors and targeted proteomic searches of plasma and cerebrospinal fluid have suggested additional markers in sporadic cases of FTLD that will lead to the identification of patients with TDP-43 or tau histopathology.

SUMMARY

Great progress has been made in developing biomarkers for FTLD, but additional work is needed to extend these advances so that the histopathologic abnormality causing FTLD can be specified in an individual patient.

Neuroimaging findings in frontotemporal lobar degeneration spectrum of disorders

Frontotemporal lobar degeneration (FTLD) is a clinically and pathologically heterogeneous spectrum of disorders. In the last few years, neuroimaging has contributed to the phenotypic characterisation of these patients. Complementary to the clinical and neuropsychological evaluations, structural magnetic resonance imaging (MRI) and functional techniques provide important pieces of information for the diagnosis of FTLD. They also appear to be useful in distinguishing FTLD from patients with Alzheimer's disease (AD). Preliminary studies in pathologically proven cases suggested that distinct patterns of tissue loss could assist in predicting in vivo the pathological subtype. Recent years have also witnessed impressive advances in the development of novel imaging approaches. Diffusion tensor MRI and functional MRI have improved our understanding of the pathophysiology of the disease, and this should lead to the identification of additional useful markers of disease progression. This reviews discusses comprehensively the state-of-the-art of neuroimaging in the study of FTLD spectrum of disorders, and attempts to envisage which will be new neuroimaging biomarkers that could serve as surrogate measures of the underlying pathology. This will be central in the design of treatment trials of experimental drugs, which are likely to emerge in the near future, to target the pathological processes associated with this condition.

Progress in the last decade in our understanding of primary progressive aphasia

Primary progressive aphasia (PPA) is a focal neurodegeneration of the brain affecting the language network. Patients can have isolated language impairment for years without impairment in other areas. PPA is classified as primary progressive nonfluent aphasia (PNFA), semantic dementia (SD), and logopenic aphasia, which have distinct patterns of atrophy on neuroimaging. PNFA and SD are included under frontotemporal lobar degenerations. PNFA patients have effortful speech with agrammatism, which is frequently associated with apraxia of speech and demonstrate atrophy in the left Broca’s area and surrounding region on neuroimaging. Patients with SD have dysnomia with loss of word and object (or face) meaning with asymmetric anterior temporal lobe atrophy. Logopenic aphasics have word finding difficulties with frequent pauses in conversation, intact grammar, and word comprehension but impaired repetition for sentences. The atrophy is predominantly in the left posterior temporal and inferior parietal regions. Recent studies have described several progranulin mutations on chromosome 17 in PNFA. The three clinical syndromes have a less robust relationship to the underlying pathology, which is heterogeneous and includes tauopathy, ubiquitinopathy, Pick’s disease, corticobasal degeneration, progressive supranuclear palsy, and Alzheimer’s disease. Recent studies, however, seem to indicate that a better characterization of the clinical phenotype (apraxic, agrammatic, semantic, logopenic, jargon) increases the predictive value of the underlying pathology. Substantial advances have been made in our understanding of PPAs but developing new biomarkers is essential in making accurate causative diagnoses in individual patients. This is critically important in the development and evaluation of disease-modifying drugs.

Classification of primary progressive aphasia and its variants

This article provides a classification of primary progressive aphasia (PPA) and its 3 main variants to improve the uniformity of case reporting and the reliability of research results. Criteria for the 3 variants of PPA--nonfluent/agrammatic, semantic, and logopenic--were developed by an international group of PPA investigators who convened on 3 occasions to operationalize earlier published clinical descriptions for PPA subtypes. Patients are first diagnosed with PPA and are then divided into clinical variants based on specific speech and language features characteristic of each subtype. Classification can then be further specified as "imaging-supported" if the expected pattern of atrophy is found and "with definite pathology" if pathologic or genetic data are available. The working recommendations are presented in lists of features, and suggested assessment tasks are also provided. These recommendations have been widely agreed upon by a large group of experts and should be used to ensure consistency of PPA classification in future studies. Future collaborations will collect prospective data to identify relationships between each of these syndromes and specific biomarkers for a more detailed understanding of clinicopathologic correlations.

The new classification of primary progressive aphasia into semantic, logopenic, or nonfluent/agrammatic variants

Primary progressive aphasia (PPA), typically resulting from a neurodegenerative disease such as frontotemporal lobar degeneration or Alzheimer's disease, is characterized by a progressive loss of specific language functions with relative sparing of other cognitive domains. Three variants of PPA are now recognized: semantic variant, logopenic variant, and nonfluent/agrammatic variant. We discuss recent work characterizing the neurolinguistic, neuropsychological, imaging and pathologic profiles associated with these variants. Improved reliability of diagnoses will be increasingly important as trials for etiology-specific treatments become available. We also discuss the implications of these syndromes for theories of language function.

Primary progressive aphasia: clinicopathological correlations

Primary progressive aphasia (PPA) is a disorder of declining language that is a frequent presentation of neurodegenerative diseases such as frontotemporal lobar degeneration. Three variants of PPA are recognized: progressive nonfluent aphasia, semantic dementia, and logopenic progressive aphasia. In an era of etiology-specific treatments for neurodegenerative conditions, determining the histopathological basis of PPA is crucial. Clinicopathological correlations in PPA emphasize the contributory role of dementia with Pick bodies and other tauopathies, TDP-43 proteinopathies, and Alzheimer disease. These data suggest an association between a specific PPA variant and an underlying pathology, although many cases of PPA are associated with an unexpected pathology. Neuroimaging and biofluid biomarkers are now emerging as important adjuncts to clinical diagnosis. There is great hope that the addition of biomarker assessments to careful clinical examination will enable accurate diagnosis of the pathology associated with PPA during a patient's life, and that such findings will serve as the basis for clinical trials in this spectrum of disease.

Abeta amyloid and glucose metabolism in three variants of primary progressive aphasia

OBJECTIVE

Alzheimer's disease (AD) is found at autopsy in up to one third of patients with primary progressive aphasia (PPA), but clinical features that predict AD pathology in PPA are not well defined. We studied the relationships between language presentation, Abeta amyloidosis, and glucose metabolism in three PPA variants using [11C]-Pittsburgh compound B ([11C]PIB) and [18F]-labeled fluorodeoxyglucose positron emission tomography ([18F]FDG-PET).

METHODS

Patients meeting PPA criteria (N = 15) were classified as logopenic aphasia (LPA), progressive nonfluent aphasia (PNFA), or semantic dementia (SD) based on language testing. [11C]PIB distribution volume ratios were calculated using Logan graphical analysis (cerebellar reference). [18F]FDG images were normalized to pons. Partial volume correction was applied.

RESULTS

Elevated cortical PIB (by visual inspection) was more common in LPA (4/4 patients) than in PNFA (1/6) and SD (1/5) (p < 0.02). In PIB-positive PPA, PIB uptake was diffuse and indistinguishable from the pattern in matched AD patients (n = 10). FDG patterns were focal and varied by PPA subtype, with left temporoparietal hypometabolism in LPA, left frontal hypometabolism in PNFA, and left anterior temporal hypometabolism in SD. FDG uptake was significant asymmetric (favoring left hypometabolism) in PPA (p < 0.005) but not in AD.

INTERPRETATION

LPA is associated with Abeta amyloidosis, suggesting that subclassification of PPA based on language features can help predict the likelihood of AD pathology. Language phenotype in PPA is closely related to metabolic changes that are focal and anatomically distinct between subtypes, but not to amyloid deposition patterns that are diffuse and similar to AD.

The logopenic/phonological variant of primary progressive aphasia

OBJECTIVE

Primary progressive aphasia (PPA) is characterized by isolated decline in language functions. Semantic dementia and progressive nonfluent aphasia are accepted PPA variants. A "logopenic" variant (LPA) has also been proposed, but its cognitive and anatomic profile is less defined. The aim of this study was to establish the cognitive and anatomic features of LPA.

METHODS

Six previously unreported LPA cases underwent extensive neuropsychological evaluation and an experimental study of phonological loop functions, including auditory and visual span tasks with digits, letters, and words. For each patient, a voxel-wise, automated analysis of MRI or SPECT data were conducted using SPM2.

RESULTS

In LPA, speech rate was slow, with long word-finding pauses. Grammar and articulation were preserved, although phonological paraphasias could be present. Repetition and comprehension were impaired for sentences but preserved for single words, and naming was moderately affected. Investigation of phonological loop functions showed that patients were severely impaired in digit, letter, and word span tasks. Performance did not improve with pointing, was influenced by word length, and did not show the normal phonological similarity effect. Atrophy or decreased blood flow was consistently found in the posterior portion of the left superior and middle temporal gyri and inferior parietal lobule.

CONCLUSIONS

Logopenic progressive aphasia (LPA) is a distinctive variant of primary progressive aphasia. Cognitive and neuroimaging data indicate that a deficit in phonological loop functions may be the core mechanism underlying the LPA clinical syndrome. Recent studies suggest that Alzheimer disease may be the most common pathology underlying the LPA clinical syndrome.

Links between frontotemporal lobar degeneration, corticobasal degeneration, progressive supranuclear palsy, and amyotrophic lateral sclerosis

Frontotemporal lobar degeneration, corticobasal degeneration (CBD), progressive supranuclear palsy, and amyotrophic lateral sclerosis have been considered distinct clinicopathologic entities with few issues in common other than neurodegeneration being central to all. The aim of this paper is to highlight the clinical, topographic, pathologic, proteomic, and genetic similarities among these disorders and the syndromes through which each disorder is exhibited. The critical roles of tau and TAR DNA-binding protein 43 (TDP-43) dysfunction in the disorders and syndromes are emphasized. Although confusion certainly remains, and the ability to predict the underlying proteinopathy in the various neurodegenerative syndromes is far from perfect, there is optimism that insights gained over the next few years will enhance our ability to accurately identify the amyloidopathies, tauopathies, and TDP-43opathies early in the disease course, potentially improving the ability to impact these diseases once targeted therapies have been developed.

Word-finding difficulty: a clinical analysis of the progressive aphasias

The patient with word-finding difficulty presents a common and challenging clinical problem. The complaint of 'word-finding difficulty' covers a wide range of clinical phenomena and may signify any of a number of distinct pathophysiological processes. Although it occurs in a variety of clinical contexts, word-finding difficulty generally presents a diagnostic conundrum when it occurs as a leading or apparently isolated symptom, most often as the harbinger of degenerative disease: the progressive aphasias. Recent advances in the neurobiology of the focal, language-based dementias have transformed our understanding of these processes and the ways in which they breakdown in different diseases, but translation of this knowledge to the bedside is far from straightforward. Speech and language disturbances in the dementias present unique diagnostic and conceptual problems that are not fully captured by classical models derived from the study of vascular and other acute focal brain lesions. This has led to a reformulation of our understanding of how language is organized in the brain. In this review we seek to provide the clinical neurologist with a practical and theoretical bridge between the patient presenting with word-finding difficulty in the clinic and the evidence of the brain sciences. We delineate key illustrative speech and language syndromes in the degenerative dementias, compare these syndromes with the syndromes of acute brain damage, and indicate how the clinical syndromes relate to emerging neurolinguistic, neuroanatomical and neurobiological insights. We propose a conceptual framework for the analysis of word-finding difficulty, in order both better to define the patient's complaint and its differential diagnosis for the clinician and to identify unresolved issues as a stimulus to future work.

A review on primary progressive aphasia

Primary progressive aphasia (PPA) is a neurodegenerative disease of insidious onset presenting with progressive isolated loss of language function, without significant impairment in other cognitive domains. Current diagnostic criteria require the language dysfunction to remain isolated for at least two years, and to remain the salient feature as the disease progresses, usually to involve other domains such as behavior, executive functions, and judgment. Although PPA in its early stages can usually be differentiated from probable Alzheimer's disease (PRAD) and the behavioral variant of frontotemporal lobar degeneration by the absence of significant changes in memory and behavior, and the preservation of activities daily living, progression of the disease often leads to deficits more consistent with the latter. Underlying etiologies remain heterogeneous: the neuropathological characteristics associated with frontotemporal lobar degeneration, cortocobasal degeneration, and motor neuron disease are usually found. There is a strong genetic susceptibility with affliction of first-degree relatives with similar disease in up to 40 to 50% in some series. Pathogenic mutations in genes coding for the proteins tau and progranulin have been isolated. These are leading to a better understanding of the neuropathological mechanisms and hopefully targeted disease-modifying therapy. Current therapy is limited to improving mood symptoms and targeting behavior changes as they develop. Referral to specialized centers where speech therapy, counseling, and education for both patient and caregiver are available may be helpful.