Disordered network structure and function in dystonia: pathological connectivity vs. adaptive responses

Primary dystonia is thought to emerge through abnormal functional relationships between basal ganglia and cerebellar motor circuits. These interactions may differ across disease subtypes and provide a novel biomarker for diagnosis and treatment. Using a network mapping algorithm based on resting-state functional MRI (rs-fMRI), a method that is readily implemented on conventional MRI scanners, we identified similar disease topographies in hereditary dystonia associated with the DYT1 or DYT6 mutations and in sporadic patients lacking these mutations. Both networks were characterized by contributions from the basal ganglia, cerebellum, thalamus, sensorimotor areas, as well as cortical association regions. Expression levels for the two networks were elevated in hereditary and sporadic dystonia, and in non-manifesting carriers of dystonia mutations. Nonetheless, the distribution of abnormal functional connections differed across groups, as did metrics of network organization and efficiency in key modules. Despite these differences, network expression correlated with dystonia motor ratings, significantly improving the accuracy of predictions based on thalamocortical tract integrity obtained with diffusion tensor MRI (DTI). Thus, in addition to providing unique information regarding the anatomy of abnormal brain circuits, rs-fMRI functional networks may provide a widely accessible method to help in the objective evaluation of new treatments for this disorder.

Adaptive and pathological connectivity responses in Parkinson's disease brain networks

Functional imaging has been used extensively to identify and validate disease-specific networks as biomarkers in neurodegenerative disorders. It is not known, however, whether the connectivity patterns in these networks differ with disease progression compared to the beneficial adaptations that may also occur over time. To distinguish the 2 responses, we focused on assortativity, the tendency for network connections to link nodes with similar properties. High assortativity is associated with unstable, inefficient flow through the network. Low assortativity, by contrast, involves more diverse connections that are also more robust and efficient. We found that in Parkinson's disease (PD), network assortativity increased over time. Assoratitivty was high in clinically aggressive genetic variants but was low for genes associated with slow progression. Dopaminergic treatment increased assortativity despite improving motor symptoms, but subthalamic gene therapy, which remodels PD networks, reduced this measure compared to sham surgery. Stereotyped changes in connectivity patterns underlie disease progression and treatment responses in PD networks.

Functional brain networks in the evaluation of patients with neurodegenerative disorders

Network analytical tools are increasingly being applied to brain imaging maps of resting metabolic activity (PET) or blood oxygenation-dependent signals (functional MRI) to characterize the abnormal neural circuitry that underlies brain diseases. This approach is particularly valuable for the study of neurodegenerative disorders, which are characterized by stereotyped spread of pathology along discrete neural pathways. Identification and validation of disease-specific brain networks facilitate the quantitative assessment of pathway changes over time and during the course of treatment. Network abnormalities can often be identified before symptom onset and can be used to track disease progression even in the preclinical period. Likewise, network activity can be modulated by treatment and might therefore be used as a marker of efficacy in clinical trials. Finally, early differential diagnosis can be achieved by simultaneously measuring the activity levels of multiple disease networks in an individual patient's scans. Although these techniques were originally developed for PET, over the past several years analogous methods have been introduced for functional MRI, a more accessible non-invasive imaging modality. This advance is expected to broaden the application of network tools to large and diverse patient populations.

Stereotyped Relationship Between Motor and Cognitive Metabolic Networks in Parkinson's Disease

BACKGROUND

Idiopathic Parkinson's disease (iPD) is associated with two distinct brain networks, PD-related pattern (PDRP) and PD-related cognitive pattern (PDCP), which correlate respectively with motor and cognitive symptoms. The relationship between the two networks in individual patients is unclear.

OBJECTIVE

To determine whether a consistent relationship exists between these networks, we measured the difference between PDRP and PDCP expression, termed delta, on an individual basis in independent populations of patients with iPD (n = 356), patients with idiopathic REM sleep behavioral disorder (iRBD) (n = 21), patients with genotypic PD (gPD) carrying GBA1 variants (n = 12) or the LRRK2-G2019S mutation (n = 14), patients with atypical parkinsonian syndromes (n = 238), and healthy control subjects (n = 95) from the United States, Slovenia, India, and South Korea.

METHODS

We used [18 F]-fluorodeoxyglucose positron emission tomography and resting-state fMRI to quantify delta and to compare the measure across samples; changes in delta over time were likewise assessed in longitudinal patient samples. Lastly, we evaluated delta in prodromal individuals with iRBD and subjects with gPD.

RESULTS

Delta was abnormally elevated in each of the four iPD samples (P < 0.05), as well as in the at-risk iRBD group (P < 0.05), with increasing values over time (P < 0.001). PDRP predominance was also present in gPD, with higher values in patients with GBA1 variants compared with the less aggressive LRRK2-G2019S mutation (P = 0.005). This trend was not observed in patients with atypical parkinsonian syndromes, who were accurately discriminated from iPD based on PDRP expression and delta (area under the curve = 0.85; P < 0.0001).

CONCLUSIONS

PDRP predominance, quantified by delta, assays the spread of dysfunction from motor to cognitive networks in patients with PD. Delta may therefore aid in differential diagnosis and in tracking disease progression in individual patients. © 2022 International Parkinson and Movement Disorder Society.

Diplopia in Parkinson's disease: Indication of a cortical phenotype with cognitive dysfunction?

BACKGROUND

Visual disturbances are increasingly recognized as common non-motor symptoms in Parkinson's disease (PD). In PD patients, intermittent diplopia has been found to be associated with the presence of visual hallucinations and the Parkinson's psychosis spectrum. Here, we investigated whether diplopia in PD is associated with other non-motor traits and cognitive impairment.

METHODS

We investigated 50 non-demented PD patients with and without intermittent diplopia and 24 healthy controls for visual disturbances, as well as motor and non-motor symptoms. All participants underwent a neuropsychological test battery; visuospatial abilities were further evaluated with subtests of the Visual Object and Space Perception Battery (VOSP). The two PD patient groups did not differ significantly in age, symptom duration, motor symptom severity, frequency of visual hallucinations, or visual sensory efficiency.

RESULTS

PD patients with diplopia reported more frequent non-motor symptoms including more subjective cognitive problems and apathy without changes in global cognition measures compared to those without diplopia. PD patients with diplopia had greater impairment in several tests of visuospatial function (pentagon copying p = .002; number location p = .001; cube analysis p < .02) and object perception (p < .001) compared to PD patients without diplopia and healthy controls. By contrast, no consistent group differences were observed in executive function, memory, or language.

CONCLUSIONS

PD patients with diplopia have a greater non-motor symptom burden and deficits in visuospatial function compared to PD patients without diplopia. PD patients with diplopia might be prone to a cortical phenotype with cognitive decline and apathy associated with worse prognosis.

Cognition-Related Functional Topographies in Parkinson's Disease: Localized Loss of the Ventral Default Mode Network

Cognitive dysfunction in Parkinson's disease (PD) is associated with increased expression of the PD cognition-related pattern (PDCP), which overlaps with the normal default mode network (DMN). Here, we sought to determine the degree to which the former network represents loss of the latter as a manifestation of the disease process. To address this, we first analyzed metabolic images (fluorodeoxyglucose positron emission tomography [PET]) from a large PD sample with varying cognitive performance. Cognitive impairment in these patients correlated with increased PDCP expression as well as DMN loss. We next determined the spatial relationship of the 2 topographies at the subnetwork level. To this end, we analyzed resting-state functional magnetic resonance imaging (rs-fMRI) data from an independent population. This approach uncovered a significant PD cognition-related network that resembled previously identified PET- and rs-fMRI-based PDCP topographies. Further analysis revealed selective loss of the ventral DMN subnetwork (precuneus and posterior cingulate cortex) in PD, whereas the anterior and posterior components were not affected by the disease. Importantly, the PDCP also included a number of non-DMN regions such as the dorsolateral prefrontal and medial temporal cortex. The findings show that the PDCP is a reproducible cognition-related network that is topographically distinct from the normal DMN.

Metabolic Network Abnormalities in Drug-Naïve Parkinson's Disease

BACKGROUND

An ideal imaging biomarker for a neurodegenerative disorder should be able to measure abnormalities in the earliest stages of the disease.

OBJECTIVE

We investigated metabolic network changes in two independent cohorts of drug-naïve Parkinson's disease (PD) patients who have not been exposed to dopaminergic medication.

METHODS

We scanned 85 de novo, drug-naïve PD patients and 85 age-matched healthy control subjects from Italy (n = 96) and the United States (n = 74) with [¹⁸ F]-fluorodeoxyglucose PET. All patients had clinical follow-ups to verify the diagnosis of idiopathic PD. Spatial covariance analysis was used to identify and validate de novo PD-related metabolic patterns in the Italian and U.S. cohorts. We compared the de novo PD-related metabolic patterns to the original PD-related pattern that was identified in more advanced patients who had been on chronic dopaminergic treatment.

RESULTS

De novo PD-related metabolic patterns were identified in each of the two independent cohorts of drug-naïve PD patients, and each differentiated PD patients from healthy control subjects. Expression values for these disease patterns were elevated in drug-naïve PD patients relative to healthy controls in the identification as well as in each of the validation subgroups. The two de novo PD-related metabolic patterns were topographically very similar to each other and to the original PD-related pattern.

CONCLUSIONS

Reproducible PD-related patterns are expressed in de novo, drug-naïve PD patients. In PD, disease-related metabolic patterns have stereotyped topographies that develop independently of chronic levodopa treatment. © 2019 International Parkinson and Movement Disorder Society.

LRRK2 and GBA Variants Exert Distinct Influences on Parkinson's Disease-Specific Metabolic Networks

The natural history of idiopathic Parkinson's disease (PD) varies considerably across patients. While PD is generally sporadic, there are known genetic influences: the two most common, mutations in the LRRK2 or GBA1 gene, are associated with slower and more aggressive progression, respectively. Here, we applied graph theory to metabolic brain imaging to understand the effects of genotype on the organization of previously established PD-specific networks. We found that closely matched PD patient groups with the LRRK2-G2019S mutation (PD-LRRK2) or GBA1 variants (PD-GBA) expressed the same disease networks as sporadic disease (sPD), but PD-LRRK2 and PD-GBA patients exhibited abnormal increases in network connectivity that were not present in sPD. Using a community detection strategy, we found that the location and modular distribution of these connections differed strikingly across genotypes. In PD-LRRK2, connections were gained within the network core, with the formation of distinct functional pathways linking the cerebellum and putamen. In PD-GBA, by contrast, the majority of functional connections were formed outside the core, involving corticocortical pathways at the network periphery. Strategically localized connections within the core in PD-LRRK2 may maintain PD network activity at lower levels than in PD-GBA, resulting in a less aggressive clinical course.

Restless legs syndrome is a relevant comorbidity in patients with inflammatory bowel disease

BACKGROUND AND AIMS

In patients with inflammatory bowel disease (IBD), restless legs syndrome (RLS) may occur as an extraintestinal disease manifestation. Iron deficiency (ID) or folate deficiency/vitamin B₁₂ deficiency (FD/VB₁₂D) has previously been described to cause RLS. Here, we determined the prevalence and severity of RLS in IBD patients and evaluated the effect of iron and/or folic acid/vitamin B₁₂ supplementation.

METHODS

Patients were screened for ID and RLS by a gastroenterologist. If RLS was suspected, a neurologist was consulted for definitive diagnosis and severity. Patients with RLS and ID, FD, or VB₁₂D received supplementation and were followed-up at weeks 4 and 11 after starting supplementation.

RESULTS

A total of 353 IBD patients were included. Prevalence for RLS was 9.4% in Crohn's disease (CD) and 8% in ulcerative colitis (UC). Prevalence for the subgroup of clinically relevant RLS (symptoms ≥ twice/week with at least moderate distress) was 7.1% (n = 16) for CD and 4.8% (n = 6) for UC. 38.7% of RLS patients presented with ID, FD, and/or VB₁₂D. Most frequently ID was seen (25.8%; n = 8). Iron supplementation resulted in RLS improvement (p = 0.029) at week 4 in seven out of eight patients.

CONCLUSION

Although the overall prevalence of RLS in IBD did not differ to the general population, clinically relevant RLS was more frequent in IBD patients and, therefore, it is important for clinicians to be aware of RLS symptoms. Though for definite diagnosis and proper treatment of RLS, a neurologist must be consulted. Additionally, iron supplementation of IBD patients with ID can improve RLS symptoms.

TRIAL REGISTRATION

ClinicalTrials.gov No. NCT03457571.

Assessment of thrombus length in acute ischemic stroke by post-contrast magnetic resonance angiography

OBJECTIVES

Post-contrast magnetic resonance angiography (PC-MRA) enables visualization of vessel segments distal to an intra-arterial thrombus in acute ischemic stroke. We hypothesized that PC-MRA also allows clot length measurement in different intracranial vessels.

METHODS

Patients with MRI-confirmed ischemic stroke and intracranial artery occlusion within 24 hours of symptom onset were prospectively evaluated. PC-MRA was added to a standard stroke MRI protocol. Thrombus length was measured on thick slab maximum intensity projection images. Clinical outcome at hospital discharge was assessed by modified Rankin Scale (mRS).

RESULTS

Thirty-four patients (median age 72 years) presenting with a median National Institutes of Health Stroke Scale score of 11 and a median onset to imaging time of 116 min were included. PC-MRA enabled precise depiction of proximal and distal terminus of the thrombus in 31 patients (91%), whereas in three patients (9%) PC-MRA presented a partial occlusion. Median thrombus length in patients with complete occlusion was 9.9 mm. In patients with poor outcome (mRS ≥3) median thrombus length was significantly longer than in those with good outcome (mRS ≤2;P=0.011).

CONCLUSIONS

PC-MRA demonstrates intra-arterial thrombus length at different vessel occlusion sites. Longer thrombus length is associated with poor clinical outcome.

CLINICAL TRIAL REGISTRATION

NCT02077582; Results.

Increased putamen hypercapnic vasoreactivity in levodopa-induced dyskinesia

In a rodent model of Parkinson's disease (PD), levodopa-induced involuntary movements have been linked to striatal angiogenesis - a process that is difficult to document in living human subjects. Angiogenesis can be accompanied by localized increases in cerebral blood flow (CBF) responses to hypercapnia. We therefore explored the possibility that, in the absence of levodopa, local hypercapnic CBF responses are abnormally increased in PD patients with levodopa-induced dyskinesias (LID) but not in their nondyskinetic (NLID) counterparts. We used H215O PET to scan 24 unmedicated PD subjects (12 LID and 12 NLID) and 12 matched healthy subjects in the rest state under normocapnic and hypercapnic conditions. Hypercapnic CBF responses were compared to corresponding levodopa responses from the same subjects. Group differences in hypercapnic vasoreactivity were significant only in the posterior putamen, with greater CBF responses in LID subjects compared with the other subjects. Hypercapnic and levodopa-mediated CBF responses measured in this region exhibited distinct associations with disease severity: the former correlated with off-state motor disability ratings but not symptom duration, whereas the latter correlated with symptom duration but not motor disability. These are the first in vivo human findings linking LID to microvascular changes in the basal ganglia.

Spot Sign in Acute Intracerebral Hemorrhage in Dynamic T1-Weighted Magnetic Resonance Imaging

BACKGROUND AND PURPOSE

In computed tomographic imaging of acute intracerebral hemorrhage spot sign on computed tomographic angiography has been established as a marker for hematoma expansion and poor clinical outcome. Although, magnetic resonance imaging (MRI) can accurately visualize acute intracerebral hemorrhage, a corresponding MRI marker is lacking to date.

METHODS

We prospectively examined 50 consecutive patients with acute intracerebral hemorrhage within 24 hours of symptom onset. The MRI protocol consisted of a standard stroke protocol and dynamic contrast-enhanced T1-weighted imaging with a time resolution of 7.07 s/batch. Stroke scores were assessed at admission and at time of discharge. Volume measurements of hematoma size and spot sign were performed with MRIcron.

RESULTS

Contrast extravasation within sites of the hemorrhage (MRI spot sign) was seen in 46% of the patients. Patients with an MRI spot sign had a significantly shorter time to imaging than those without (P<0.001). The clinical outcome measured by the modified Rankin Scale was significantly worse in patients with spot sign compared with those without (P≤0.001). Hematoma expansion was observed in the spot sign group compared with the nonspot sign group, although the differences were not significant.

CONCLUSIONS

Spot sign can be detected using MRI on postcontrast T1-weighted and dynamic T1-weighted images. It is associated with worse clinical outcome. The time course of contrast extravasation in dynamic T1 images indicates that these spots represent ongoing bleeding.

Dysfunctional action control as a specific feature of Parkinson's disease

Parkinson's disease (PD) is characterised by motor deficits as well as cognitive alterations, particularly concerning frontal lobe control. Here, we were interested in whether executive function is abnormal already early in PD, as well as whether this dysfunction worsens as a part of the dementia in PD. The following groups engaged in tasks addressing action control: PD patients with mild and advanced motor symptoms (aPD) without dementia, PD patients with dementia (PDD), patients with Alzheimer's disease (AD) and healthy subjects (CON). Subjects either had to perform or inhibit button presses upon go and no-go cues, respectively. These cues were preceded by pre-cues, either randomly instructive of right or left hand preparation (switch condition), or repetitively instructive for one side only (non-switch condition). PDD and aPD omitted more go responses than CON. Furthermore, PDD disproportionally committed failures upon no-go cues compared to CON. In the non-switch condition, PDD performed worse than AD, whose deficits increased to the level of PDD in the switch condition. Over all PD patients, task performance correlated with disease severity. Under the switch condition, task performance was low in both PDD and AD. In the non-switch condition, this also held true for advanced PD patients (with and without dementia), but not for AD. Thus, the deficits evident in PDD appear to develop from imbalanced inhibitory-to-excitatory action control generally inherent to PD. These results specify the concept of dysexecution in PD and differentiate the cognitive profile of PDD from that of AD patients.