Diffusion magnetic resonance imaging-derived free water detects neurodegenerative pattern induced by interferon-γ

Functional and free-water imaging in rapid eye movement behaviour disorder and Parkinson's disease

It is established that one of the best predictors of a future diagnosis of Parkinson's disease is a current diagnosis of rapid eye movement behaviour disorder (RBD). In such patients, this provides a unique opportunity to study brain physiology and behavioural motor features of RBD that may precede early-stage Parkinson's disease. Based on prior work in early-stage Parkinson's disease, we aim to determine if the function of corticostriatal and cerebellar regions are impaired in RBD using task-based functional MRI and if structural changes can be detected within the caudate, putamen and substantia nigra in RBD using free-water imaging. To assess motor function, we measured performance on the Purdue Pegboard Test, which is affected in patients with RBD and Parkinson's disease. A cohort of 24 RBD, 39 early-stage Parkinson's disease and 25 controls were investigated. All participants were imaged at 3 Telsa. Individuals performed a unimanual grip force task during functional imaging. Participants also completed scales to assess cognition, sleep and motor symptoms. We found decreased functional activity in both RBD and Parkinson's disease within the motor cortex, caudate, putamen and thalamus compared with controls. There was elevated free-water-corrected fractional anisotropy in the putamen in RBD and Parkinson's disease and elevated free-water in the putamen and posterior substantia nigra in Parkinson's disease compared with controls. Participants with RBD and Parkinson's disease performed significantly worse on all tasks of the Purdue Pegboard Test compared with controls. The both hands task of the Purdue Pegboard Test was most sensitive in distinguishing between groups. A subgroup analysis of early-stage RBD (<2 years diagnosis) confirmed similar findings as those in the larger RBD group. These findings provide new evidence that the putamen is affected in early-stage RBD using both functional and free-water imaging. We also found evidence that the striatum, thalamus and motor cortex have reduced functional activity in early-stage RBD and Parkinson's disease. While the substantia nigra shows elevated free-water in Parkinson's disease, we did not observe this effect in early-stage RBD. These findings point to the corticostriatal and thalamocortical circuits being impaired in RBD patients.

Lithium Aspartate for Long COVID Fatigue and Cognitive Dysfunction: A Randomized Clinical Trial

Importance

Neurologic post-COVID-19 condition (PCC), or long COVID, symptoms of fatigue and cognitive dysfunction continue to affect millions of people who have been infected with SARS-CoV-2. There currently are no effective evidence-based therapies available for treating neurologic PCC.

Objective

To assess the effects of lithium aspartate therapy on PCC fatigue and cognitive dysfunction.

Design, Setting, and Participants

A randomized, double-blind, placebo-controlled trial (RCT) enrolling participants in a neurology clinic from November 28, 2022, to June 29, 2023, with 3 weeks of follow-up, was conducted. Subsequently, an open-label lithium dose-finding study with 6 weeks of follow-up was performed among the same participants enrolled in the RCT. Eligible individuals needed to report new, bothersome fatigue or cognitive dysfunction persisting for more than 4 weeks after a self-reported positive test for COVID-19, Fatigue Severity Scale-7 (FSS-7) or Brain Fog Severity Scale (BFSS) score of 28 or greater, Beck Depression Inventory-II score less than 24, and no history of a condition known to cause fatigue or cognitive dysfunction. All participants in the RCT were eligible for the dose-finding study, except for those who responded to the placebo. Intention-to-treat analysis was used.

Intervention

Lithium aspartate, 10 to 15 mg/d, or identically appearing placebo for 3 weeks followed by open-label lithium aspartate, 10 to 15 mg/d, for 2 weeks. In the subsequent dose-finding study, open-label lithium aspartate dosages up to 45 mg/d for 6 weeks were given.

Main Outcomes and Measures

Change in sum of FSS-7 and BFSS scores. The scores for each measure range from 7 to 49, with higher scores indicating more severe symptoms. Secondary outcomes included changes from baseline in the scores of additional questionnaires.

Results

Fifty-two participants were enrolled (30 [58%] males; mean [SD] age, 58.54 [14.34] years) and 26 were randomized to treatment with lithium aspartate (10 females) and 26 to placebo (12 female). Two participants assigned to lithium aspartate were lost to follow-up and none withdrew. No adverse events were attributable to lithium therapy. There were no significant intergroup differences for the primary outcome (-3.6; 95% CI, -16.6 to 9.5; P = .59) or any secondary outcomes. Among 3 patients completing a subsequent dose-finding study, open-label lithium aspartate, 40 to 45 mg/d, was associated with numerically greater reductions in fatigue and cognitive dysfunction scores than 15 mg/d, particularly in 2 patients with serum lithium levels of 0.18 and 0.49 mEq/L compared with 1 patient with a level of 0.10 mEq/L.

Conclusions and Relevance

In this RCT, therapy with lithium aspartate, 10 to 15 mg/d, was ineffective for neurologic PCC fatigue and cognitive dysfunction. Another RCT is required to assess the potential benefits of higher lithium dosages for treating neurologic PCC.

Trial Registration

ClinicalTrials.gov Identifier: NCT05618587 and NCT06108297.

Glymphatic system dysfunction in mood disorders: Evaluation by diffusion magnetic resonance imaging

The glymphatic system, an expansive cerebral waste-disposal network, harbors myriad enigmatic facets necessitating elucidation of their nexus with diverse pathologies. Murine investigations have revealed a relationship between the glymphatic system and affective disorders. This study aimed to illuminate the interplay between bipolar disorder and the glymphatic system. Fifty-eight individuals afflicted with bipolar disorder were identified through meticulous psychiatric assessment. These individuals were juxtaposed with a cohort of 66 comparably aged and sex-matched, mentally stable subjects. Subsequent analysis entailed the application of covariance analysis to evaluate along with the perivascular space (ALPS) index, a novel magnetic resonance imaging method for assessing brain interstitial fluid dynamics via diffusion tensor imaging within the bipolar and control cohorts. We also evaluated the correlation between the ALPS index and clinical parameters, which included the Hamilton Depression scale scores, disease duration, and other clinical assessments. Moreover, partial correlation analyses, incorporating age and sex as covariates, were performed to investigate the relationships between the ALPS index and clinical measures within the two cohorts. A noteworthy adverse correlation was observed between the ALPS index and illness duration. A free-water imaging analysis revealed a substantial elevation in the free-water index within the white-matter tracts, prominently centered on the corpus callosum, within the bipolar cohort relative to that in the control group. In analogous cerebral regions, a conspicuous affirmative correlation was observed between the free-water-corrected radial diffusivity and depression rating scales. Our results showed that the protracted course of bipolar disorder concomitantly exacerbated glymphatic system dysregulation.

Transcallosal white matter and cortical gray matter variations in autistic adults ages 30-73 years: A bi-tensor free water imaging approach

Background: Autism spectrum disorder (ASD) has long been recognized as a lifelong condition, but brain aging studies in autistic adults aged >30 years are limited. Free water, a novel brain imaging marker derived from diffusion MRI (dMRI), has shown promise in differentiating typical and pathological aging and monitoring brain degeneration. We aimed to examine free water and free water corrected dMRI measures to assess white and gray matter microstructure and their associations with age in autistic adults. Methods: Forty-three autistic adults ages 30-73 years and 43 age, sex, and IQ matched neurotypical controls participated in this cross-sectional study. We quantified fractional anisotropy (FA), free water, and free water-corrected FA (fwcFA) across 32 transcallosal white matter tracts and 94 gray matter areas in autistic adults and neurotypical controls. Follow-up analyses assessed age effect on dMRI metrics of the whole brain for both groups and the relationship between dMRI metrics and clinical measures of ASD in regions that significantly differentiated autistic adults from controls. Results: We found globally elevated free water in 24 transcallosal tracts in autistic adults. We identified negligible differences in dMRI metrics in gray matter between the two groups. Age-associated FA reductions and free water increases were featured in neurotypical controls; however, this brain aging profile was largely absent in autistic adults. Additionally, greater autism quotient (AQ) total raw score was associated with increased free water in the inferior frontal gyrus pars orbitalis and lateral orbital gyrus in autistic adults. Limitations: All autistic adults were cognitively capable individuals, minimizing the generalizability of the research findings across the spectrum. This study also involved a cross-sectional design, which limited inferences about the longitudinal microstructural changes of white and gray matter in ASD. Conclusions: We identified differential microstructural configurations between white and gray matter in autistic adults and that autistic individuals present more heterogeneous brain aging profiles compared to controls. Our clinical correlation analysis offered new evidence that elevated free water in some localized white matter tracts may critically contribute to autistic traits in ASD. Our findings underscored the importance of quantifying free water in dMRI studies of ASD.

Quantifying neuroinflammation within deep gray matter in small vessel disease using diffusion tensor based free-water imaging: a longitudinal study

Purpose

Employing free water (FW) imaging, a cutting-edge diffusion MRI technique, we assessed neuroinflammation within deep gray matter (DGM) in small vessel disease (SVD) over 1-2 years.

Method

One hundred and seventy SVD patients and 21 healthy controls (HCs) underwent MRI scans and neuropsychological evaluations at baseline. These patients were then categorized into two groups: 67 displayed no cognitive impairment (NCI), while 103 exhibited vascular mild cognitive impairment (VaMCI). A follow-up study 1-2 years later included 23 from the NCI group and 28 from the VaMCI group. Calculation of FW values within DGM facilitated both cross-sectional and longitudinal analysis, revealing partial correlations between FW value changes and cognitive function alternations.

Results

Baseline examinations disclosed significant differences in DGM FW values among the three participant groups. We found increased mean FW values in the left pulvinar (Pul), bilateral lateral nuclei (LN) and bilateral internal medullary lamina of the thalamus in VaMCI participants compared with their NCI counterparts in longitudinal analysis. Notably, negative associations emerged between the FW value changes in the left Pul and the right LN of the thalamus and MoCA score changes in the VaMCI group over 1-2 years.

Conclusions

These findings support the hypothesis that increased FW value is present at the preclinical stage of SVD and remains persistent during the early course of the disease, potentially acting as the biomarker for the mechanism of underlying cognitive decline in SVD.

Basal forebrain integrity, cholinergic innervation and cognition in idiopathic Parkinson's disease

Most individuals with Parkinson's disease experience cognitive decline. Mounting evidence suggests this is partially caused by cholinergic denervation due to α-synuclein pathology in the cholinergic basal forebrain. Alpha-synuclein deposition causes inflammation, which can be measured with free water fraction, a diffusion MRI-derived metric of extracellular water. Prior studies have shown an association between basal forebrain integrity and cognition, cholinergic levels and cognition, and basal forebrain volume and acetylcholine, but no study has directly investigated whether basal forebrain physiology mediates the relationship between acetylcholine and cognition in Parkinson's disease. We investigated the relationship between these variables in a cross-sectional analysis of 101 individuals with Parkinson's disease. Cholinergic levels were measured using fluorine-18 fluoroethoxybenzovesamicol (18F-FEOBV) PET imaging. Cholinergic innervation regions of interest included the medial, lateral capsular and lateral perisylvian regions and the hippocampus. Brain volume and free water fraction were quantified using T1 and diffusion MRI, respectively. Cognitive measures included composites of attention/working memory, executive function, immediate memory and delayed memory. Data were entered into parallel mediation analyses with the cholinergic projection areas as predictors, cholinergic basal forebrain volume and free water fraction as mediators and each cognitive domain as outcomes. All mediation analyses controlled for age, years of education, levodopa equivalency dose and systolic blood pressure. The basal forebrain integrity metrics fully mediated the relationship between lateral capsular and lateral perisylvian acetylcholine and attention/working memory, and partially mediated the relationship between medial acetylcholine and attention/working memory. Basal forebrain integrity metrics fully mediated the relationship between medial, lateral capsular and lateral perisylvian acetylcholine and free water fraction. For all mediations in attention/working memory and executive function, the free water mediation was significant, while the volume mediation was not. The basal forebrain integrity metrics fully mediated the relationship between hippocampal acetylcholine and delayed memory and partially mediated the relationship between lateral capsular and lateral perisylvian acetylcholine and delayed memory. The volume mediation was significant for the hippocampal and lateral perisylvian models, while free water fraction was not. Free water fraction in the cholinergic basal forebrain mediated the relationship between acetylcholine and attention/working memory and executive function, while cholinergic basal forebrain volume mediated the relationship between acetylcholine in temporal regions in memory. These findings suggest that these two metrics reflect different stages of neurodegenerative processes and add additional evidence for a relationship between pathology in the basal forebrain, acetylcholine denervation and cognitive decline in Parkinson's disease.

Longitudinal Free-Water Changes in Dementia with Lewy Bodies

BACKGROUND

Diffusion-weighted magnetic resonance imaging (dMRI) examines tissue microstructure integrity in vivo. Prior dementia with Lewy bodies (DLB) diffusion tensor imaging studies yielded mixed results.

OBJECTIVE

We employed free-water (FW) imaging to assess DLB progression and correlate with clinical decline in DLB.

METHODS

Baseline and follow-up MRIs were obtained at 12 and/or 24 months for 27 individuals with DLB or mild cognitive impairment with Lewy bodies (MCI-LB). FW was analyzed using the Mayo Clinic Adult Lifespan Template. Primary outcomes were FW differences between baseline and 12 or 24 months. To compare FW change longitudinally, we included 20 cognitively unimpaired individuals from the Alzheimer's Disease Neuroimaging Initiative.

RESULTS

We followed 23 participants to 12 months and 16 participants to 24 months. Both groups had worsening in Montreal Cognitive Assessment (MoCA) and Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) scores. We found significant FW increases at both time points compared to baseline in the insula, amygdala, posterior cingulum, parahippocampal, entorhinal, supramarginal, fusiform, retrosplenial, and Rolandic operculum regions. At 24 months, we found more widespread microstructural changes in regions implicated in visuospatial processing, motor, and cholinergic functions. Between-group analyses (DLB vs. controls) confirmed significant FW changes over 24 months in most of these regions. FW changes were associated with longitudinal worsening of MDS-UPDRS and MoCA scores.

CONCLUSIONS

FW increased in gray and white matter regions in DLB, likely due to neurodegenerative pathology associated with disease progression. FW change was associated with clinical decline. The findings support dMRI as a promising tool to track disease progression in DLB. © 2024 International Parkinson and Movement Disorder Society.

Free-Water Imaging of the Nucleus Basalis of Meynert in Patients With Idiopathic REM Sleep Behavior Disorder and Parkinson Disease

BACKGROUND AND OBJECTIVES

Cognitive impairments are common in idiopathic REM sleep behavior disorder (iRBD), in which the cholinergic degeneration of nucleus basalis of Meynert (NBM) may play an important role. However, the progressive changes of NBM, the relationship between progressive NBM degeneration and progression of cognitive impairments, and whether degeneration of the NBM can predict cognitive decline in patients with iRBD remain unclear. This study aimed to investigate the cross-sectional and longitudinal microstructural alterations in the NBM of patients with iRBD using free-water imaging and whether free water in the NBM is related to cognitive, mood, and autonomic function.

METHODS

We compared the baseline free-water values in the NBM between 59 healthy controls (HCs), 57 patients with iRBD, 57 patients with Parkinson disease (PD) with normal cognition (PD-NC), and 64 patients with PD with cognitive impairment (PD-CI). Thirty patients with iRBD and 40 HCs had one longitudinal data. In patients with iRBD, we explored the associations between baseline and longitudinal changes of free-water values in the NBM and clinical characteristics and whether baseline free-water values in the NBM could predict cognitive decline.

RESULTS

IRBD, PD-NC, and PD-CI groups had significantly increased free-water values in the NBM compared with HCs, whereas PD-CI had higher free-water values compared with iRBD and PD-NC. In patients with iRBD, free-water values in the NBM were progressively elevated over follow-up and correlated with the progression of cognitive impairment and depression. Free-water values in the NBM could predict cognitive decline in the iRBD group. Furthermore, we found that patients with iRBD with cognitive impairment had higher relative change of free-water value in the NBM compared with patients with iRBD with normal cognition over follow-up.

DISCUSSION

This study proves that free-water values in the NBM are elevated cross-sectionally and longitudinally and are associated with the progression of cognitive impairment and depression in patients with iRBD. Moreover, the free-water value in the NBM can predict cognitive decline in patients with iRBD. Whether free-water imaging of the NBM has the potential to be a marker for monitoring progressive cognitive impairment and predicting the conversion to dementia in synucleinopathies needs further investigation.

Free-water diffusion magnetic resonance imaging under selegiline treatment in Parkinson's disease

INTRODUCTION

Monoamine oxidase type B inhibitors, including selegiline, are established as anti-Parkinsonian Drugs. Inhibition of monoamine oxidase type B enzymes might suppress the inflammation because of inhibition to generate reactive oxygen species. However, its effect on brain microstructure remains unclear. The aim of this study is to elucidate white matter and substantia nigra (SN) microstructural differences between Patients with Parkinson's disease with and without selegiline treatment by two independently recruited cohorts.

METHODS

Diffusion tensor imaging and free water imaging indices of WM and SN were compared among 22/15 Patients with Parkinson's disease with selegiline (PDselegiline(+)), 33/23 Patients with Parkinson's disease without selegiline (PDselegiline(-)), and 25/20 controls, in the first/second cohorts. Two cohorts were analyzed with different MRI protocols.

RESULTS

Diffusion tensor imaging and free-water indices of major white matter tracts were significantly differed between the PDselegiline(-) and controls in both cohorts, although not between the PDselegiline(+) and controls except for restricted areas. Compared with the PDselegiline(+), free-water was significantly higher in the PDselegiline(-) in the inferior fronto-occipital fasciculus, superior longitudinal fasciculus, and superior and posterior corona radiata (first cohort) and the forceps major and splenium of the corpus callosum (second cohort). There were no significant differences in free-water of anterior or posterior substantia nigra between PDselegiline(+) and PDselegiline(-).

CONCLUSIONS

Selegiline treatment might reduce the white matter microstructural abnormalities detected by free-water imaging in Parkinson's disease.

Lower fractional anisotropy without evidence for neuro-inflammation in patients with early-phase schizophrenia spectrum disorders

Various lines of research suggest immune dysregulation as a potential therapeutic target for negative and cognitive symptoms in schizophrenia spectrum disorders (SSD). Immune dysregulation would lead to higher extracellular free-water (EFW) in cerebral white matter (WM), which may partially underlie the frequently reported lower fractional anisotropy (FA) in SSD. We aim to investigate differences in EFW concentrations - a presumed proxy for neuro-inflammation - between early-phase SSD patients (n = 55) and healthy controls (HC; n = 37), and to explore immunological and cognitive correlates. To increase specificity for EFW, we study several complementary magnetic resonance imaging contrasts that are sensitive to EFW. FA, mean diffusivity (MD), magnetization transfer ratio (MTR), myelin water fraction (MWF) and quantitative T1 and T2 were calculated from diffusion-weighted imaging (DWI), magnetization transfer imaging (MTI) and multicomponent driven equilibrium single-pulse observation of T1/T2 (mcDESPOT). For each measure, WM skeletons were constructed with tract-based spatial statistics. Multivariate SSD-HC comparisons with WM skeletons and their average values (i.e. global WM) were not statistically significant. In voxel-wise analyses, FA was significantly lower in SSD in the genu of the corpus callosum and in the left superior longitudinal fasciculus (p < 0.04). Global WM measures did not correlate with immunological markers (i.e. IL1-RA, IL-6, IL-8, IL-10 and CRP) or cognition in HC and SSD after corrections for multiple comparisons. We confirmed lower FA in early-phase SSD patients. However, nonFA measures did not provide additional evidence for immune dysregulation or for higher EFW as the primary mechanism underlying the reported lower FA values in SSD.

Cortical microstructural associations with CSF amyloid and pTau

Diffusion MRI (dMRI) can be used to probe microstructural properties of brain tissue and holds great promise as a means to non-invasively map Alzheimer's disease (AD) pathology. Few studies have evaluated multi-shell dMRI models such as neurite orientation dispersion and density imaging (NODDI) and mean apparent propagator (MAP)-MRI in cortical gray matter where many of the earliest histopathological changes occur in AD. Here, we investigated the relationship between CSF pTau181 and Aβ1-42 burden and regional cortical NODDI and MAP-MRI indices in 46 cognitively unimpaired individuals, 18 with mild cognitive impairment, and two with dementia (mean age: 71.8 ± 6.2 years) from the Alzheimer's Disease Neuroimaging Initiative. We compared findings to more conventional cortical thickness measures. Lower CSF Aβ1-42 and higher pTau181 were associated with cortical dMRI measures reflecting less hindered or restricted diffusion and greater diffusivity. Cortical dMRI measures, but not cortical thickness measures, were more widely associated with Aβ1-42 than pTau181 and better distinguished Aβ+ from Aβ- participants than pTau+ from pTau- participants. dMRI associations mediated the relationship between CSF markers and delayed logical memory performance, commonly impaired in early AD. dMRI metrics sensitive to early AD pathogenesis and microstructural damage may be better measures of subtle neurodegeneration in comparison to standard cortical thickness and help to elucidate mechanisms underlying cognitive decline.

Cortico-basal ganglia white matter microstructure is linked to restricted repetitive behavior in autism spectrum disorder

BACKGROUND

Restricted repetitive behavior (RRB) is one of two behavioral domains required for the diagnosis of autism spectrum disorder (ASD). Neuroimaging is widely used to study brain alterations associated with ASD and the domain of social and communication deficits, but there has been less work regarding brain alterations linked to RRB.

METHODS

We utilized neuroimaging data from the National Institute of Mental Health Data Archive to assess basal ganglia and cerebellum structure in a cohort of children and adolescents with ASD compared to typically developing (TD) controls. We evaluated regional gray matter volumes from T1-weighted anatomical scans and assessed diffusion-weighted scans to quantify white matter microstructure with free-water imaging. We also investigated the interaction of biological sex and ASD diagnosis on these measures, and their correlation with clinical scales of RRB.

RESULTS

Individuals with ASD had significantly lower free-water corrected fractional anisotropy (FAT) and higher free-water (FW) in cortico-basal ganglia white matter tracts. These microstructural differences did not interact with biological sex. Moreover, both FAT and FW in basal ganglia white matter tracts significantly correlated with measures of RRB. In contrast, we found no significant difference in basal ganglia or cerebellar gray matter volumes.

LIMITATIONS

The basal ganglia and cerebellar regions in this study were selected due to their hypothesized relevance to RRB. Differences between ASD and TD individuals that may occur outside the basal ganglia and cerebellum, and their potential relationship to RRB, were not evaluated.

CONCLUSIONS

These new findings demonstrate that cortico-basal ganglia white matter microstructure is altered in ASD and linked to RRB. FW in cortico-basal ganglia and intra-basal ganglia white matter was more sensitive to group differences in ASD, whereas cortico-basal ganglia FAT was more closely linked to RRB. In contrast, basal ganglia and cerebellar volumes did not differ in ASD. There was no interaction between ASD diagnosis and sex-related differences in brain structure. Future diffusion imaging investigations in ASD may benefit from free-water estimation and correction in order to better understand how white matter is affected in ASD, and how such measures are linked to RRB.

Magnetic Resonance Imaging and Nuclear Imaging of Parkinsonian Disorders: Where do we go from here?

Parkinsonian disorders are a heterogeneous group of incurable neurodegenerative diseases that significantly reduce quality of life and constitute a substantial economic burden. Nuclear imaging (NI) and magnetic resonance imaging (MRI) have played and continue to play a key role in research aimed at understanding and monitoring these disorders. MRI is cheaper, more accessible, nonirradiating, and better at measuring biological structures and hemodynamics than NI. NI, on the other hand, can track molecular processes, which may be crucial for the development of efficient diseasemodifying therapies. Given the strengths and weaknesses of NI and MRI, how can they best be applied to Parkinsonism research going forward? This review aims to examine the effectiveness of NI and MRI in three areas of Parkinsonism research (differential diagnosis, prodromal disease identification, and disease monitoring) to highlight where they can be most impactful. Based on the available literature, MRI can assist with differential diagnosis, prodromal disease identification, and disease monitoring as well as NI. However, more work is needed, to confirm the value of MRI for monitoring prodromal disease and predicting phenoconversion. Although NI can complement or be a substitute for MRI in all the areas covered in this review, we believe that its most meaningful impact will emerge once reliable Parkinsonian proteinopathy tracers become available. Future work in tracer development and high-field imaging will continue to influence the landscape for NI and MRI.

Neuroinflammation and Mitochondrial Dysfunction in Parkinson's Disease: Connecting Neuroimaging with Pathophysiology

There is a pressing need for disease-modifying therapies in patients suffering from neurodegenerative diseases, including Parkinson's disease (PD). However, these disorders face unique challenges in clinical trial designs to assess the neuroprotective properties of potential drug candidates. One of these challenges relates to the often unknown individual disease mechanisms that would, however, be relevant for targeted treatment strategies. Neuroinflammation and mitochondrial dysfunction are two proposed pathophysiological hallmarks and are considered to be highly interconnected in PD. Innovative neuroimaging methods can potentially help to gain deeper insights into one's predominant disease mechanisms, can facilitate patient stratification in clinical trials, and could potentially map treatment responses. This review aims to highlight the role of neuroinflammation and mitochondrial dysfunction in patients with PD (PwPD). We will specifically introduce different neuroimaging modalities, their respective technical hurdles and challenges, and their implementation into clinical practice. We will gather preliminary evidence for their potential use in PD research and discuss opportunities for future clinical trials.

Shared and distinct white matter abnormalities in adolescent-onset schizophrenia and adolescent-onset psychotic bipolar disorder

BACKGROUND

While adolescent-onset schizophrenia (ADO-SCZ) and adolescent-onset bipolar disorder with psychosis (psychotic ADO-BPD) present a more severe clinical course than their adult forms, their pathophysiology is poorly understood. Here, we study potentially state- and trait-related white matter diffusion-weighted magnetic resonance imaging (dMRI) abnormalities along the adolescent-onset psychosis continuum to address this need.

METHODS

Forty-eight individuals with ADO-SCZ (20 female/28 male), 15 individuals with psychotic ADO-BPD (7 female/8 male), and 35 healthy controls (HCs, 18 female/17 male) underwent dMRI and clinical assessments. Maps of extracellular free-water (FW) and fractional anisotropy of cellular tissue (FAT) were compared between individuals with psychosis and HCs using tract-based spatial statistics and FSL's Randomise. FAT and FW values were extracted, averaged across all voxels that demonstrated group differences, and then utilized to test for the influence of age, medication, age of onset, duration of illness, symptom severity, and intelligence.

RESULTS

Individuals with adolescent-onset psychosis exhibited pronounced FW and FAT abnormalities compared to HCs. FAT reductions were spatially more widespread in ADO-SCZ. FW increases, however, were only present in psychotic ADO-BPD. In HCs, but not in individuals with adolescent-onset psychosis, FAT was positively related to age.

CONCLUSIONS

We observe evidence for cellular (FAT) and extracellular (FW) white matter abnormalities in adolescent-onset psychosis. Although cellular white matter abnormalities were more prominent in ADO-SCZ, such alterations may reflect a shared trait, i.e. neurodevelopmental pathology, present across the psychosis spectrum. Extracellular abnormalities were evident in psychotic ADO-BPD, potentially indicating a more dynamic, state-dependent brain reaction to psychosis.

Distinct cortical and subcortical predictors of Purdue Pegboard decline in Parkinson's disease and atypical parkinsonism

Objective measures of disease progression are critically needed in research on Parkinson's disease (PD) and atypical Parkinsonism but may be hindered by both practicality and cost. The Purdue Pegboard Test (PPT) is objective, has high test-retest reliability, and has a low cost. The goals of this study were to determine: (1) longitudinal changes in PPT in a multisite cohort of patients with PD, atypical Parkinsonism, and healthy controls; (2) whether PPT performance reflects brain pathology revealed by neuroimaging; (3) quantify kinematic deficits shown by PD patients during PPT. Parkinsonian patients showed a decline in PPT performance that correlated with motor symptom progression, which was not seen in controls. Neuroimaging measures from basal ganglia were significant predictors of PPT performance in PD, whereas cortical, basal ganglia, and cerebellar regions were predictors for atypical Parkinsonism. Accelerometry in a subset of PD patients showed a diminished range of acceleration and irregular patterns of acceleration, which correlated with PPT scores.

Lithium's effects on therapeutic targets and MRI biomarkers in Parkinson's disease: A pilot clinical trial

Background

Lithium has a wide range of neuroprotective actions, has been effective in Parkinson's disease (PD) animal models and may account for the decreased risk of PD in smokers.

Methods

This open-label pilot clinical trial randomized 16 PD patients to "high-dose" (n = 5, lithium carbonate titrated to achieve serum level of 0.4-0.5 mmol/L), "medium-dose" (n = 6, 45 mg/day lithium aspartate) or "low-dose" (n = 5, 15 mg/day lithium aspartate) lithium therapy for 24-weeks. Peripheral blood mononuclear cell (PBMC) mRNA expression of nuclear receptor-related-1 (Nurr1) and superoxide dismutase-1 (SOD1) were assessed by qPCR in addition to other PD therapeutic targets. Two patients from each group received multi-shell diffusion MRI scans to assess for free water (FW) changes in the dorsomedial nucleus of the thalamus and nucleus basalis of Meynert, which reflect cognitive decline in PD, and the posterior substantia nigra, which reflects motor decline in PD.

Results

Two of the six patients receiving medium-dose lithium therapy withdrew due to side effects. Medium-dose lithium therapy was associated with the greatest numerical increases in PBMC Nurr1 and SOD1 expression (679% and 127%, respectively). Also, medium-dose lithium therapy was the only dosage associated with mean numerical decreases in brain FW in all three regions of interest, which is the opposite of the known longitudinal FW changes in PD.

Conclusion

Medium-dose lithium aspartate therapy was associated with engagement of blood-based therapeutic targets and improvements in MRI disease-progression biomarkers but was poorly tolerated in 33% of patients. Further PD clinical research is merited examining lithium's tolerability, effects on biomarkers and potential disease-modifying effects.

Cortical microstructural associations with CSF amyloid and pTau

Diffusion MRI (dMRI) can be used to probe microstructural properties of brain tissue and holds great promise as a means to non-invasively map Alzheimer's disease (AD) pathology. Few studies have evaluated multi-shell dMRI models, such as neurite orientation dispersion and density imaging (NODDI) and mean apparent propagator (MAP)-MRI, in cortical gray matter where many of the earliest histopathological changes occur in AD. Here, we investigated the relationship between CSF pTau181 and Aβ1-42 burden and regional cortical NODDI and MAP-MRI indices in 46 cognitively unimpaired individuals, 18 with mild cognitive impairment, and two with dementia (mean age: 71.8±6.2 years) from the Alzheimer's Disease Neuroimaging Initiative. We compared findings to more conventional cortical thickness measures. Lower CSF Aβ1-42 and higher pTau181 were associated with cortical dMRI measures reflecting less hindered or restricted diffusion and greater diffusivity. Cortical dMRI measures were more widely associated with Aβ1-42 than pTau181 and better distinguished Aβ+ from Aβ- participants than pTau+/- participants. Conversely, cortical thickness was more tightly linked with pTau181. dMRI associations mediated the relationship between CSF markers and delayed logical memory performance, commonly impaired in early AD. dMRI measures sensitive to early AD pathogenesis and microstructural damage may elucidate mechanisms underlying cognitive decline.

Free-Water Imaging of the Substantia Nigra in GBA Pathogenic Variant Carriers

BACKGROUND

Pathogenic variants in the glucocerebrosidase gene (GBA) have been identified as the most common genetic risk factor for Parkinson's disease (PD). However, the features of substantia nigra damage in GBA pathogenic variant carriers remain unclear.

OBJECTIVE

We aimed to evaluate the microstructural changes in the substantia nigra in non-manifesting GBA pathogenic variant carriers (GBA-NMC) and PD patients with GBA pathogenic variant (GBA-PD) with free-water imaging.

METHODS

First, we compared free water values in the posterior substantia nigra between non-manifesting non-carriers (NMNC, n = 29), GBA-NMC (n = 26), and GBA-PD (n = 16). Then, free water values in the posterior substantia nigra were compared between GBA-PD and early- (n = 19) and late-onset (n = 40) idiopathic PD (iPD) patients. Furthermore, we examined whether the baseline free water values could predict the progressions of clinical symptoms.

RESULTS

The free water values in the posterior substantia nigra were significantly higher in the GBA-NMC and GBA-PD groups compared to NMNC, and were significantly increased in the GBA-PD group than both early- and late-onset iPD. Free water values in the posterior substantia nigra could predict the progression of anxiety and cognitive decline in GBA-NMC and GBA-PD groups.

CONCLUSIONS

We demonstrate that free water values are elevated in the substantia nigra and predict the development of non-motor symptoms in GBA-NMC and GBA-PD. Our findings demonstrate that a significant nigral impairment already exists in GBA-NMC, and nigral injury may be more severe in GBA-PD than in iPD. These results support that free-water imaging can as a potential early marker of substantia nigra damage. © 2023 International Parkinson and Movement Disorder Society.

Free water imaging as a novel biomarker in Wilson's disease: A cross-sectional study

BACKGROUND

The bi-tensor free water imaging may provide more specific information in detecting microstructural brain tissue alterations than conventional single tensor diffusion tensor imaging. The study aimed to investigate microstructural changes in deep gray matter (DGM) nuclei of Wilson's disease (WD) using a bi-tensor free water imaging and whether the findings correlate with the neurological impairment in WD patients.

METHODS

The study included 29 WD patients and 25 controls. Free water and free water corrected fractional anisotropy (FA_T) in DGM nuclei of WD patients were calculated. The correlations of free water and FA_T with the Unified WD Rating Scale (UWDRS) neurological subscale of WD patients were performed.

RESULTS

Free water and FA_T values were significantly increased in multiple DGM nuclei of neurological WD patients compared to controls. WD patients with normal appearing on conventional MRI also had significantly higher free water and FA_T values in multiple DGM nuclei than controls. Positive correlations were noted between the UWDRS neurological subscores and free water values of the putamen and pontine tegmentum as well as FA_T values of the dentate nucleus, red nucleus, and globus pallidus. In addition, the measured free water and FA_T values of specific structures also showed a positive correlation with specific clinical symptoms in neurological WD patients, such as dysarthria, parkinsonian signs, tremor, dystonia, and ataxia.

CONCLUSIONS

Free water imaging detects microstructural changes in both normal and abnormal appearing DGM nuclei of WD patients. Free water imaging indices were correlated with the severity of neurological impairment in WD patients.

In vivo detection of substantia nigra and locus coeruleus volume loss in Parkinson's disease using neuromelanin-sensitive MRI: Replication in two cohorts

Patients with Parkinson's disease undergo a loss of melanized neurons in substantia nigra pars compacta and locus coeruleus. Very few studies have assessed substantia nigra pars compacta and locus coeruleus pathology in Parkinson's disease simultaneously with magnetic resonance imaging (MRI). Neuromelanin-sensitive MRI measures of substantia nigra pars compacta and locus coeruleus volume based on explicit magnetization transfer contrast have been shown to have high scan-rescan reproducibility in controls, but no study has replicated detection of Parkinson's disease-associated volume loss in substantia nigra pars compacta and locus coeruleus in multiple cohorts with the same methodology. Two separate cohorts of Parkinson's disease patients and controls were recruited from the Emory Movement Disorders Clinic and scanned on two different MRI scanners. In cohort 1, imaging data from 19 controls and 22 Parkinson's disease patients were acquired with a Siemens Trio 3 Tesla scanner using a 2D gradient echo sequence with magnetization transfer preparation pulse. Cohort 2 consisted of 33 controls and 39 Parkinson's disease patients who were scanned on a Siemens Prisma 3 Tesla scanner with a similar imaging protocol. Locus coeruleus and substantia nigra pars compacta volumes were segmented in both cohorts. Substantia nigra pars compacta volume (Cohort 1: p = 0.0148; Cohort 2: p = 0.0011) and locus coeruleus volume (Cohort 1: p = 0.0412; Cohort 2: p = 0.0056) were significantly reduced in the Parkinson's disease group as compared to controls in both cohorts. This imaging approach robustly detects Parkinson's disease effects on these structures, indicating that it is a promising marker for neurodegenerative neuromelanin loss.

Increased Free Water in the Substantia Nigra in Asymptomatic LRRK2 G2019S Mutation Carriers

BACKGROUND

The alteration of substantia nigra (SN) degeneration in populations at risk of Parkinson's disease (PD) is unclear.

OBJECTIVE

We investigated free water (FW) values in the posterior SN (pSN) in asymptomatic LRRK2 G2019S mutation carriers.

METHODS

We analyzed diffusion imaging data from 28 asymptomatic LRRK2 G2019S mutation carriers and 30 healthy controls (HCs), whereas 11 asymptomatic LRRK2 G2019S carriers and 11 HCs were followed up. FW values in the pSN were measured and compared between the groups. The relationship between longitudinal changes in FW in the pSN and dopamine transporter striatal binding ratio (SBR) was analyzed.

RESULTS

FW values in the pSN were significantly elevated and kept increasing during follow-up in asymptomatic LRRK2 G2019S carriers. There was a negative correlation between FW changes in the left pSN and SBR changes in the left putamen.

CONCLUSION

FW in the pSN has the potential to be a progression imaging marker of early dopaminergic degeneration in the population at risk of PD. © 2022 International Parkinson and Movement Disorder Society.

Quantitative Susceptibility Mapping and Free Water Imaging of Substantia Nigra in Parkinson's Disease

BACKGROUND

The utility of imaging methods to detect iron content in the substantia nigra pars compacta (SNc) and free water imaging in the posterior substantia nigra (pSN) has the potential to be imaging markers for the detection of Parkinson's disease (PD).

OBJECTIVE

This study aimed to compare the discriminative power of above methods, and whether the combination can improve the diagnostic potential of PD.

METHODS

Quantitative susceptibility mapping (QSM) and diffusion-weighted data were obtained from 41 healthy controls (HC), 37 patients with idiopathic REM sleep behavior disorder (RBD), and 65 patients with PD. Mean QSM values of bilateral SNc and mean isotropic volume fraction (Viso) values of bilateral pSN (mean QSM|Viso values of bilateral SNc|pSN) were separately calculated and compared among the groups.

RESULTS

Mean QSM|Viso values of bilateral SNc|pSN were significantly higher for RBD and PD patients compared to HC and were significantly higher in PD patients than in RBD patients. The power of the mean QSM|Viso values of bilateral SNc|pSN and combined mean QSM and Viso values was 0.873, 0.870, and 0.961 in discriminating PD and HC, 0.779, 0.719, and 0.864 in discriminating RBD from HC, 0.634, 0.636, and 0.689 in discriminating PD and RBD patients.

CONCLUSION

QSM and free water imaging have similar discriminative power in the detection of prodromal and clinical PD, while combination of these two methods increases discriminative power. Our findings suggest that the combination of QSM and free water imaging has the potential to become an imaging marker for the diagnosis of PD.

Nigral volumetric and microstructural measures in individuals with scans without evidence of dopaminergic deficit

Introduction

Striatal dopamine transporter (DAT) imaging using ¹²³I-ioflupane single photon positron emitted computed tomography (SPECT) (DaTScan, GE) identifies 5-20% of newly diagnosed Parkinson's disease (PD) subjects enrolling in clinical studies to have scans without evidence of dopaminergic deficit (SWEDD). These individuals meet diagnostic criteria for PD, but do not clinically progress as expected, and they are not believed to have neurodegenerative Parkinsonism. Inclusion of SWEDD participants in PD biomarker studies or therapeutic trials may therefore cause them to fail. DaTScan can identify SWEDD individuals, but it is expensive and not widely available; an alternative imaging approach is needed. Here, we evaluate the use of neuromelanin-sensitive, iron-sensitive, and diffusion contrasts in substantia nigra pars compacta (SNpc) to differentiate SWEDD from PD individuals.

Methods

Neuromelanin-sensitive, iron-sensitive, and diffusion imaging data for SWEDD, PD, and control subjects were downloaded from the Parkinson's progression markers initiative (PPMI) database. SNpc volume, SNpc iron (R ₂), and SNpc free water (FW) were measured for each participant.

Results

Significantly smaller SNpc volume was seen in PD as compared to SWEDD (P < 10^-3) and control (P < 10^-3) subjects. SNpc FW was elevated in the PD group relative to controls (P = 0.017). No group difference was observed in SNpc R ₂.

Conclusion

In conclusion, nigral volume and FW in the SWEDD group were similar to that of controls, while a reduction in nigral volume and increased FW were observed in the PD group relative to SWEDD and control participants. These results suggest that these MRI measures should be explored as a cost-effective alternative to DaTScan for evaluation of the nigrostriatal system.

Free Water Fraction Predicts Cognitive Decline for Individuals with Idiopathic Parkinson's disease

INTRODUCTION

Free water fraction (FWF) is considered a metric of microstructural integrity and may be useful in predicting cognitive decline in idiopathic Parkinson's Disease (PD). We sought to determine if higher FWF within the dorsal portion of the caudate nucleus and basal nucleus of Meynert, two regions associated with cognitive decline in PD, predict change in cognition over a two-year span. Due to the existence of cognitive and neurophysiological subgroups within PD, we statistically categorized participants based on FWF in these regions.

METHODS

At baseline, participants completed a research cognitive protocol followed by MRI structural and diffusion metrics. We used k-means cluster analysis with average FWF values from bilateral basal nucleus of Meynert and dorsal caudate to create data-driven FWF clusters for baseline. Two-year reliable change indices were calculated for metrics of language, visuospatial, memory, cognitive flexibility, and reasoning domains. Reliable change scores were compared between the clusters and non-PD peers.

RESULTS

Baseline participants included 174 participants (112 PD, 62 non-PD). Cluster analysis yielded three clusters: low FWF in both regions of interest (ROIs), high FWF in both ROIs, and moderate FWF in both ROIs. Reliable change analyses were completed on 93 participants (67 PD, 26 non-PD). After controlling for age and education, the High FWF cluster declined more than non-PD peers in every domain except memory.

CONCLUSION

Individuals with high FWF in regions associated with cognitive decline in PD show significant decline across several cognitive domains compared to non-PD peers. Future research should include FWF in additional cortical regions.

Free-water imaging of the cholinergic basal forebrain and pedunculopontine nucleus in Parkinson's disease

Free-water imaging can predict and monitor dopamine system degeneration in people with Parkinson's disease. It can also enhance the sensitivity of traditional diffusion tensor imaging (DTI) metrics for indexing neurodegeneration. However, these tools are yet to be applied to investigate cholinergic system degeneration in Parkinson's disease, which involves both the pedunculopontine nucleus and cholinergic basal forebrain. Free-water imaging, free-water-corrected DTI and volumetry were used to extract structural metrics from the cholinergic basal forebrain and pedunculopontine nucleus in 99 people with Parkinson's disease and 46 age-matched controls. Cognitive ability was tracked over 4.5 years. Pearson's partial correlations revealed that free-water-corrected DTI metrics in the pedunculopontine nucleus were associated with performance on cognitive tasks that required participants to make rapid choices (behavioural flexibility). Volumetric, free-water content and DTI metrics in the cholinergic basal forebrain were elevated in a sub-group of people with Parkinson's disease with evidence of cognitive impairment, and linear mixed modelling revealed that these metrics were differently associated with current and future changes to cognition. Free water and free-water-corrected DTI can index cholinergic degeneration that could enable stratification of patients in clinical trials of cholinergic interventions for cognitive decline. In addition, degeneration of the pedunculopontine nucleus impairs behavioural flexibility in Parkinson's disease, which may explain this region's role in increased risk of falls.

Thalamic Dorsomedial Nucleus Free Water Correlates with Cognitive Decline in Parkinson's Disease

BACKGROUND

Brain diffusion tensor imaging (DTI) has been shown to reflect cognitive changes in early Parkinson's disease (PD) but the diffusion-based measure free water (FW) has not been previously assessed.

OBJECTIVES

To assess if FW in the thalamic nuclei primarily involved with cognition (ie, the dorsomedial [DMN] and anterior [AN] nuclei), the nucleus basalis of Meynert (nbM), and the hippocampus correlates with and is associated with longitudinal cognitive decline and distinguishes cognitive status at baseline in early PD. Also, to explore how FW compares with conventional DTI, FW-corrected DTI, and volumetric assessments for these outcomes.

METHODS

Imaging data and Montreal Cognitive Assessment (MoCA) scores from the Parkinson's Progression Markers Initiative database were analyzed using partial correlations and ANCOVA. Primary outcome multiple comparisons were corrected for false discovery rate (q value).

RESULTS

Thalamic DMN FW changes over 1 year correlated with MoCA changes over both 1 and 3 years (partial correlations -0.222, q = 0.040, n = 130; and - 0.229, q = 0.040, n = 123, respectively; mean PD duration at baseline = 6.85 months). NbM FW changes over 1 year only correlated with MoCA changes over 3 years (-0.222, q = 0.040). Baseline hippocampal FW was associated with cognitive impairment at 3 years (q = 0.040) and baseline nbM FW distinguished PD-normal cognition (MoCA ≥26) from PD-cognitive impairment (MoCA ≤25), (q = 0.008). The exploratory comparisons showed FW to be the most robust assessment modality for all outcomes.

CONCLUSIONS

Thalamic DMN FW is a promising cognition progression biomarker in early PD that may assist in identifying cognition protective therapies in clinical trials. FW is a robust assessment modality for these outcomes. © 2021 International Parkinson and Movement Disorder Society.

Diffusion Magnetic Resonance Imaging Detects Progression in Parkinson's Disease: A Placebo-Controlled Trial of Rasagiline

BACKGROUND

Rasagiline has received attention as a potential disease-modifying therapy for Parkinson's disease (PD). Whether rasagiline is disease modifying remains in question.

OBJECTIVE

The main objective of this study was to determine whether rasagiline has disease-modifying effects in PD over 1 year. Secondarily we evaluated two diffusion magnetic resonance imaging pulse sequences to determine the best sequence to measure disease progression.

METHODS

This prospective, randomized, double-blind, placebo-controlled trial assessed the effects of rasagiline administered at 1 mg/day over 12 months in early-stage PD. The primary outcome was 1-year change in free-water accumulation in posterior substantia nigra (pSN) measured using two diffusion magnetic resonance imaging pulse sequences, one with a repetition time (TR) of 2500 ms (short TR; n = 90) and one with a TR of 6400 ms (long TR; n = 75). Secondary clinical outcomes also were assessed.

RESULTS

Absolute change in pSN free-water accumulation was not significantly different between groups (short TR: P = 0.346; long TR: P = 0.228). No significant differences were found in any secondary clinical outcomes between groups. Long TR, but not short TR, data show pSN free-water increased significantly over 1 year (P = 0.025). Movement Disorder Society Unified Parkinson's Disease Rating Scale testing of motor function, Part III increased significantly over 1 year (P = 0.009), and baseline free-water in the pSN correlated with the 1-year change in Movement Disorder Society Unified Parkinson's Disease Rating Scale testing of motor function, Part III (P = 0.004) and 1-year change in bradykinesia score (P = 0.044).

CONCLUSIONS

We found no evidence that 1 mg/day rasagiline has a disease-modifying effect in PD over 1 year. We found pSN free-water increased over 1 year, and baseline free-water relates to clinical motor progression, demonstrating the importance of diffusion imaging parameters for detecting and predicting PD progression. © 2021 International Parkinson and Movement Disorder Society.

Pursuit of precision medicine: Systems biology approaches in Alzheimer's disease mouse models

Alzheimer's disease (AD) is a complex disease that is mediated by numerous factors and manifests in various forms. A systems biology approach to studying AD involves analyses of various body systems, biological scales, environmental elements, and clinical outcomes to understand the genotype to phenotype relationship that potentially drives AD development. Currently, there are many research investigations probing how modifiable and nonmodifiable factors impact AD symptom presentation. This review specifically focuses on how imaging modalities can be integrated into systems biology approaches using model mouse populations to link brain level functional and structural changes to disease onset and progression. Combining imaging and omics data promotes the classification of AD into subtypes and paves the way for precision medicine solutions to prevent and treat AD.

Emerging Neuroimaging Biomarkers Across Disease Stage in Parkinson Disease: A Review

Importance

Imaging biomarkers in Parkinson disease (PD) are increasingly important for monitoring progression in clinical trials and also have the potential to improve clinical care and management. This Review addresses a critical need to make clear the temporal relevance for diagnostic and progression imaging biomarkers to be used by clinicians and researchers over the clinical course of PD. Magnetic resonance imaging (diffusion imaging, neuromelanin-sensitive imaging, iron-sensitive imaging, T1-weighted imaging), positron emission tomography/single-photon emission computed tomography dopaminergic, serotonergic, and cholinergic imaging as well as metabolic and cerebral blood flow network neuroimaging biomarkers in the preclinical, prodromal, early, and moderate to late stages are characterized.

Observations

If a clinical trial is being carried out in the preclinical and prodromal stages, potentially useful disease-state biomarkers include dopaminergic imaging of the striatum; metabolic imaging; free-water, neuromelanin-sensitive, and iron-sensitive imaging in the substantia nigra; and T1-weighted structural magnetic resonance imaging. Disease-state biomarkers that can distinguish atypical parkinsonisms are metabolic imaging, free-water imaging, and T1-weighted imaging; dopaminergic imaging and other molecular imaging track progression in prodromal patients, whereas other established progression biomarkers need to be evaluated in prodromal cohorts. Progression in early-stage PD can be monitored using dopaminergic imaging in the striatum, metabolic imaging, and free-water and neuromelanin-sensitive imaging in the posterior substantia nigra. Progression in patients with moderate to late-stage PD can be monitored using free-water imaging in the anterior substantia nigra, R2* of substantia nigra, and metabolic imaging. Cortical thickness and gyrification might also be useful markers or predictors of progression. Dopaminergic imaging and free-water imaging detect progression over 1 year, whereas other modalities detect progression over 18 months or longer. The reliability of progression biomarkers varies with disease stage, whereas disease-state biomarkers are relatively consistent in individuals with preclinical, prodromal, early, and moderate to late-stage PD.

Conclusions and Relevance

Imaging biomarkers for various stages of PD are readily available to be used as outcome measures in clinical trials and are potentially useful in multimodal combination with routine clinical assessment. This Review provides a critically important template for considering disease stage when implementing diagnostic and progression biomarkers in both clinical trials and clinical care settings.

Cell-specific effects of Dyt1 knock-out on sensory processing, network-level connectivity, and motor deficits

DYT1 dystonia is a debilitating movement disorder characterized by repetitive, unintentional movements and postures. The disorder has been linked to mutation of the TOR1A/DYT1 gene encoding torsinA. Convergent evidence from studies in humans and animal models suggest that striatal medium spiny neurons and cholinergic neurons are important in DYT1 dystonia. What is not known is how torsinA dysfunction in these specific cell types contributes to the pathophysiology of DYT1 dystonia. In this study we sought to determine whether torsinA dysfunction in cholinergic neurons alone is sufficient to generate the sensorimotor dysfunction and brain changes associated with dystonia, or if torsinA dysfunction in a broader subset of cell types is needed. We generated two genetically modified mouse models, one with selective Dyt1 knock-out from dopamine-2 receptor expressing neurons (D2KO) and one where only cholinergic neurons are impacted (Ch2KO). We assessed motor deficits and performed in vivo 11.1 T functional MRI to assess sensory-evoked brain activation and connectivity, along with diffusion MRI to assess brain microstructure. We found that D2KO mice showed greater impairment than Ch2KO mice, including reduced sensory-evoked brain activity in key regions of the sensorimotor network, and altered functional connectivity of the striatum that correlated with motor deficits. These findings suggest that (1) the added impact of torsinA dysfunction in medium spiny and dopaminergic neurons of the basal ganglia generate more profound deficits than the dysfunction of cholinergic neurons alone, and (2) that sensory network impairments are linked to motor deficits in DYT1 dystonia.

Increased free water in the substantia nigra in idiopathic REM sleep behaviour disorder

Imaging markers sensitive to neurodegeneration in the substantia nigra are critically needed for future disease-modifying trials. Previous studies have demonstrated the utility of posterior substantia nigra free water as a marker of progression in Parkinson's disease. In this study, we tested the hypothesis that free water is elevated in the posterior substantia nigra of idiopathic REM sleep behaviour disorder, which is considered a prodromal stage of synucleinopathy. We applied free-water imaging to 32 healthy control subjects, 34 patients with idiopathic REM sleep behaviour disorder and 38 patients with Parkinson's disease. Eighteen healthy control subjects and 22 patients with idiopathic REM sleep behaviour disorder were followed up and completed longitudinal free-water imaging. Free-water values in the substantia nigra were calculated for each individual and compared among groups. We tested the associations between posterior substantia nigra free water and uptake of striatal dopamine transporter in idiopathic REM sleep behaviour disorder. Free-water values in the posterior substantia nigra were significantly higher in the patients with idiopathic REM sleep behaviour disorder patients than in the healthy control subjects, but were significantly lower in patients with idiopathic REM sleep behaviour disorder than in patients with Parkinson's disease. In addition, we observed significantly negative associations between posterior substantia nigra free-water values and dopamine transporter striatal binding ratios in the idiopathic REM sleep behaviour disorder patients. Longitudinal free-water imaging analyses were conducted with a linear mixed-effects model, and showed a significant Group × Time interaction in posterior substantia nigra, identifying increased mean free-water values in posterior substantia nigra of idiopathic REM sleep behaviour disorder over time. These results demonstrate that free water in the posterior substantia nigra is a valid imaging marker of neurodegeneration in idiopathic REM sleep behaviour disorder, which has the potential to be used as an indicator in disease-modifying trials.

A longitudinal analysis of brain extracellular free water in HIV infected individuals

Initiation of combination antiretroviral therapy (cART) reduces inflammation in HIV-infected (HIV+) individuals. Recent studies demonstrated that diffusion MRI based extracellular free water (FW) modeling can be sensitive to neuroinflammation. Here, we investigate the FW in HIV-infection, its temporal evolution, and its association with blood markers, and cognitive scores. Using 96 age-matched participants, we found that FW was significantly elevated in grey and white matter in cART-naïve HIV+ compared to HIV-uninfected (HIV−) individuals at baseline. These increased FW values positively correlated with neurofilament light chain (NfL) and negatively correlated with CD4 counts. FW in grey and white matter, as well as NfL decreased in the HIV+ after 12 weeks of cART treatment. No significant FW differences were noted between the HIV+ and HIV− cohorts at 1 and 2-year follow-up. Results suggest that FW elevation in cART-naïve HIV+ participants is likely due to neuroinflammation. The correlation between FW and NfL, and the improvement in both FW and NfL after 12 weeks of cART treatment further reinforces this conclusion. The longer follow-up at 1 and 2 years suggests that cART helped control neuroinflammation as inferred by FW. Therefore, FW could be used as a biomarker to monitor HIV-associated neuroinflammation.

Parkinson's disease progression in the substantia nigra: location, location, location

This scientific commentary refers to ‘Spatiotemporal changes in substantia nigra neuromelanin content in Parkinson’s disease’, by Biondetti et al. (doi:10.1093/brain/awaa216