Preoperative pain hypersensitivity is associated with axial pain after posterior cervical spinal surgeries in degenerative cervical myelopathy patients: a preliminary resting-state fMRI study

Abnormal preoperative fMRI signal variability in the pain ascending pathway is associated with the postoperative axial pain intensity in degenerative cervical myelopathy patients

BACKGROUND CONTEXT

The moment-to-moment variability of resting-state brain activity has been suggested to play an active role in chronic pain.

PURPOSE

To investigate preoperative alterations in regional blood-oxygen-level-dependent signal variability (BOLDsv) and inter-regional dynamic functional connectivity (dFC) in individuals with degenerative cervical myelopathy (DCM), and their potential association with postoperative axial pain severity.

STUDY DESIGN

Cross-sectional study.

PATIENT SAMPLE

Resting-state functional magnetic resonance imaging was obtained in 42 migraine individuals and 40 healthy controls (HCs).

OUTCOME MEASURES

We calculated the standard deviation (SD) of the BOLD time-series at each voxel and the SD and mean of the dynamic conditional correlation between the brain regions which showed significant group differences in BOLDsv.

METHODS

A group comparison was conducted using whole-brain voxel-wise analysis of the standard deviation (SD) of the BOLD time-series which was a measure of the BOLDsv. The brain areas displaying notable group discrepancies in BOLDsv were utilized to outline regions of interest (ROIs). To determine the strength/variability of the dFC, the mean and SD of the dynamic conditional correlation were calculated within these ROIs. Moreover, the postoperative axial pain (PAP) severity of patients was evaluated.

RESULTS

Our results revealed that DCM patients with postoperative axial pain (PAP) demonstrated considerably increased BOLDsv in the bilateral thalamus and right insular, but significantly lower BOLDsv in the right S1. By applying dynamic functional connectivity (dFC) analysis, we found that DCM patients with PAP exhibited greater fluctuation of dFC in the thalamo-cortical pathway (specifically, thalamus-S1), when compared to HCs and patients without PAP (nPAP). Lastly, we established that dysfunctional BOLDsv and dFC in the ascending pain pathway were positively associated with the severity of PAP in DCM patients.

CONCLUSION

Our results indicate a potential correlation between impaired pain ascending pathway and postoperative axial pain in DCM patients. These findings could potentially spark novel treatment approaches for individuals experiencing preoperative axial pain.

Brain MRI changes in degenerative cervical myelopathy: a systematic review

BACKGROUND

Degenerative cervical myelopathy (DCM) is the most common cause of adult spinal cord dysfunction globally. Associated neurological symptoms and signs have historically been explained by pathobiology within the cervical spine. However, recent advances in imaging have shed light on numerous brain changes in patients with DCM, and it is hypothesised that these changes contribute to DCM pathogenesis. The aetiology, significance, and distribution of these supraspinal changes is currently unknown. The objective was therefore to synthesise all current evidence on brain changes in DCM.

METHODS

A systematic review was performed. Cross-sectional and longitudinal studies with magnetic resonance imaging on a cohort of patients with DCM were eligible. PRISMA guidelines were followed. MEDLINE and Embase were searched to 28th August 2023. Duplicate title/abstract screening, data extraction and risk of bias assessments were conducted. A qualitative synthesis of the literature is presented as per the Synthesis Without Meta-Analysis (SWiM) reporting guideline. The review was registered with PROSPERO (ID: CRD42022298538).

FINDINGS

Of the 2014 studies that were screened, 47 studies were identified that used MRI to investigate brain changes in DCM. In total, 1500 patients with DCM were included in the synthesis, with a mean age of 53 years. Brain alterations on MRI were associated with DCM both before and after surgery, particularly within the sensorimotor network, visual network, default mode network, thalamus and cerebellum. Associations were commonly reported between brain MRI alterations and clinical measures, particularly the Japanese orthopaedic association (JOA) score. Risk of bias of included studies was low to moderate.

INTERPRETATION

The rapidly expanding literature provides mounting evidence for brain changes in DCM. We have identified key structures and pathways that are altered, although there remains uncertainty regarding the directionality and clinical significance of these changes. Future studies with greater sample sizes, more detailed phenotyping and longer follow-up are now needed.

FUNDING

ODM is supported by an Academic Clinical Fellowship at the University of Cambridge. BMD is supported by an NIHR Clinical Doctoral Fellowship at the University of Cambridge (NIHR300696). VFJN is supported by an NIHR Rosetrees Trust Advanced Fellowship (NIHR302544). This project was supported by an award from the Rosetrees Foundation with the Storygate Trust (A2844).

Neural correlates of central pain sensitization in chronic low back pain: a resting-state fMRI study

PURPOSE

The objective of this study is to explore the neural correlates of pain sensitization in patients with chronic low back pain (cLBP). While the association between cLBP and pain sensitization has been widely reported, the underlying brain mechanism responsible for this relationship requires further investigation.

METHODS

Our study included 56 cLBP patients and 56 healthy controls (HC). Functional magnetic resonance imaging data were obtained, and the voxel-wise amplitude of low-frequency fluctuation (ALFF) was calculated to identify brain alterations in cLBP patients compared to HC groups. Pearson correlation coefficients were computed to explore the association between clinical data and brain alterations. Furthermore, mediation analyses were performed to investigate the path association between brain alterations and pain-related behaviors.

RESULTS

Our findings revealed that patients with cLBP exhibited higher sensitivity, attention, and catastrophizing tendencies towards pain compared to HC. Furthermore, cLBP patients displayed significantly higher ALFF in various brain regions within the "pain matrix" and the default mode network when compared to HC. The altered precuneus ALFF was positively correlated with pain intensity (R = 0.51, P<0.001) and was negatively correlated with pain sensitivity (R = -0.43, P<0.001) in cLBP patients. Importantly, the effect of altered precuneus ALFF on pain intensity was mediated by pain threshold in these patients.

CONCLUSION

Our study suggests that altered neural activity in the precuneus may contribute to pain hypersensitivity, which further exacerbating pain in cLBP patients.

Deficits in the thalamocortical pathway associated with hypersensitivity to pain in patients with frozen shoulder

Background and purpose

Frozen shoulder (FS) is a chronic pain condition and has been shown to be associated with pain sensitization. However, the underyling brain mechanisms remain unclear. Here, we aimed to explore brain alterations and their association with pain sensitization in patients with FS.

Materials and methods

A total of 54 FS patients and 52 healthy controls (HCs) were included in this study. Here, we applied both structural and functional magnetic resonance imaging (MRI) techniques to investigate brain abnormalities in FS patients. Voxel-wise comparisons were performed to reveal the differences in the gray matter volume (GMV) and amplitude of low-frequency fluctuation (ALFF) between FS patients and HCs. Furthermore, the region of interest (ROI) to whole-brain functional connectivity (FC) was calculated and compared between groups. Finally, Pearson's correlation coefficients were computed to reveal the association between clinical data and brain alterations.

Results

Four main findings were observed: (1) FS patients exhibited decreased thalamus GMV, which correlated with pain intensity and pain threshold; (2) relative to HCs, FS patients exhibited a higher level of ALFF within the anterior cingulate cortex (ACC) and the thalamus; (3) FS patients exhibited a significant increase in Tha-S1 FC compared to HCs; and (4) the effect of thalamus GMV on pain intensity was mediated by pain threshold in FS patients.

Conclusion

The dysfunctional thalamus might induce pain hypersensitivity, which further aggravates the pain in FS patients.