Neuroimaging Parameters Are Not Associated With Chronic Post-stroke Fatigue in Young Stroke Patients

Understanding neural mechanisms and the use of targeted non-invasive brain stimulation for treatment of post-stroke fatigue: A scoping review

BACKGROUND

Post-stroke fatigue (PSF) is one of the most prevalent symptoms that affects quality of life and daily function after stroke. Despite a growing body of research, its pathophysiology is poorly understood. Non-invasive brain stimulation (NIBS), such as the transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), can serve as a non-pharmacological intervention for PSF. In this review, we aim to (1) evaluate PSF neuroimaging studies to deduce potential neural mechanisms, (2) describe NIBS as a tool to probe brain structures to further understand pathophysiology of fatigue, and (3) assess NIBS as a treatment intervention for PSF.

METHODS

A systematic search was conducted for the databases PubMed, Embase, Scopus, CINAHL and Cochrane. Studies were included based on the following inclusion and exclusion criteria: >18 years with PSF, use of neuroimaging and/or NIBS for investigation or as an intervention for PSF, English language, study types including cohort, case control, or randomized controlled trials. Data extracted included participant characteristics, concept, context, study methods, and key findings relevant to the review questions.

RESULTS

A total of 30 studies met criteria. Neuroimaging papers that investigated brain structure (MRI) found conflicting associations between lesion location and PSF. Functional methods (fMRI, TMS) revealed altered resting state functional connectivity (rsFC), cortical excitability, and a disruption in interhemispheric inhibitory balance as potential mechanisms of PSF. There were no studies using TMS as an intervention for PSF. Of the six articles that used tDCS, only two reported statistically significant reductions in the severity of PSF.

CONCLUSION

Structural characteristics of stroke lesions had conflicting findings, while functional neuroimaging studies suggested that altered rsFC, cortical excitability and interhemispheric inhibitory balance contribute to the development of PSF. There were inconsistent results on the effectiveness of tDCS as an intervention for PSF, due to varying methodologies and lack of precise targeting of underlying neural mechanisms. Further investigations are needed to determine if NIBS could be a potential treatment to alleviate the effects of PSF.

Clinical and neuroanatomical predictors of post-stroke fatigue

INTRODUCTION

Post-stroke fatigue (PSF) has been described as early exhaustion with tiredness that develops during physical or mental activity and generally does not improve with rest. There are inconsistent findings on the relationship between the characteristics of the ischemic brain lesion and PSF. However, some studies suggest that specific neuroanatomical and neuroplastic changes could explain post-stroke fatigue. The aim was to evaluate the severity of PSF in relation to the location and the size of the ischemic lesion in acute stroke patients to establish possible predictors of PSF.

PATIENTS AND METHODS

We performed a prospective observational study to establish potential early predictors of long-term PSF, which was assessed using the Fatigue Assessment Scale six months after ischemic stroke. After segmenting brain infarcts on Diffusion-Weighted Imaging (DWI) images, we studied the association with PSF using Voxel-Based Lesion-Symptom Mapping (VLSM).

RESULTS

Out of 104 patients, 61 (59 %) reported PSF. Female sex and history of diabetes mellitus were associated with a greater risk of developing PSF. The association of PSF with female sex was confirmed in a replication cohort of 50 patients. The ischemic lesion volume was not associated with PSF, and VBLSM analysis did not identify any specific brain area significantly associated with PSF.

CONCLUSIONS

PSF is frequent in stroke patients, especially women, even after six months. The absence of neuroanatomical correlates of PSF suggests that it is a multifactorial process with biological, psychological, and social risk factors that require further study.

Altered functional connectivity in patients with post-stroke fatigue: A resting-state fMRI study

BACKGROUND

Post-stroke fatigue (PSF) was a common complication after stroke. This study aimed to explore the neuroimaging mechanism of PSF, which was rarely studied.

METHODS

Patients with the first episode of ischemic stroke were recruited from the First Affiliated Hospital of Wenzhou Medical University between March 2021 and December 2022. The fatigue severity scale (FSS) was used to assess fatigue symptoms. PSF was diagnosed by a neurologist based on the FSS score and PSF diagnostic criteria. All the patients were scanned by resting-state functional MRI (rs-fMRI). Precuneus, the posterior node of default-mode network (pDMN), was related to fatigue. Therefore, imaging data were further analyzed by the seed-based resting-state functional connectivity (FC) approach, with the left (PCUN.L) and right precuneus (PCUN.R) being the seeds.

RESULTS

A total of 70 patients with acute ischemic stroke were finally recruited, comprising 40 patients with PSF and 30 patients without PSF. Both the PCUN.L and PCUN.R seeds (pDMN) exhibited decreased FC with the prefrontal lobes located at the anterior part of DMN (aDMN), and the FC values were negatively correlated with FSS scores (both p < 0.001). These two seeds also exhibited increased FC with the right insula, and the FC values were positively correlated with FSS scores (both p < 0.05).

CONCLUSION

The abnormal FC between the aDMN and pDMN was associated with PSF. Besides, the insula, related to interoception, might also play an important role in PSF.

Mediator complex in neurological disease

Neurological diseases, including traumatic brain injuries, stroke (haemorrhagic and ischemic), and inherent neurodegenerative diseases cause acquired disability in humans, representing a leading cause of death worldwide. The Mediator complex (MED) is a large, evolutionarily conserved multiprotein that facilities the interaction between transcription factors and RNA Polymerase II in eukaryotes. Some MED subunits have been found altered in the brain, although their specific functions in neurodegenerative diseases are not fully understood. Mutations in MED subunits were associated with a wide range of genetic diseases for MED12, MED13, MED13L, MED20, MED23, MED25, and CDK8 genes. In addition, MED12 and MED23 were deregulated in the Alzheimer's Disease. Interestingly, most of the genomic mutations have been found in the subunits of the kinase module. To date, there is only one evidence on MED1 involvement in post-stroke cognitive deficits. Although the underlying neurodegenerative disorders may be different, we are confident that the signal cascades of the biological-cognitive mechanisms of brain adaptation, which begin after brain deterioration, may also differ. Here, we analysed relevant studies in English published up to June 2023. They were identified through a search of electronic databases including PubMed, Medline, EMBASE and Scopus, including search terms such as "Mediator complex", "neurological disease", "brains". Thematic content analysis was conducted to collect and summarize all studies demonstrating MED alteration to understand the role of this central transcriptional regulatory complex in the brain. Improved and deeper knowledge of the regulatory mechanisms in neurological diseases can increase the ability of physicians to predict onset and progression, thereby improving diagnostic care and providing appropriate treatment decisions.