Altered brain morphometry in carpal tunnel syndrome is associated with median nerve pathology

Abstract

Objective Carpal tunnel syndrome (CTS) is a common median nerve entrapment neuropathy characterized by pain, paresthesias, diminished peripheral nerve conduction velocity (NCV) and maladaptive functional brain neuroplasticity. We evaluated structural reorganization in brain gray (GM) and white (WM) matter and whether such plasticity is linked to altered median nerve function in CTS. Methods We performed NCV testing, T1-weighted structural MRI, and diffusion tensor imaging (DTI) in 28 CTS and 28 age-matched healthy controls (HC). Voxel-based morphometry (VBM) contrasted regional GM volume for CTS versus HC. Significant clusters were correlated with clinical metrics and served as seeds to define associated WM tracts using DTI data and probabilistic tractography. Within these WM tracts, fractional anisotropy (FA), axial (AD) and radial (RD) diffusivity were evaluated for group differences and correlations with clinical metrics. Results For CTS subjects, GM volume was significantly reduced in contralesional S1 (hand-area), pulvinar and frontal pole. GM volume in contralesional S1 correlated with median NCV. NCV was also correlated with RD and was negatively correlated with FA within U-fiber cortico-cortical association tracts identified from the contralesional S1 VBM seed. Conclusions Our study identified clear morphometric changes in the CTS brain. This central morphometric change is likely secondary to peripheral nerve pathology and altered somatosensory afference. Enhanced axonal coherence and myelination within cortico-cortical tracts connecting primary somatosensory and motor areas may accompany peripheral nerve deafferentation. As structural plasticity was correlated with NCV and not symptomatology, the former may be a better determinant of appropriate clinical intervention for CTS, including surgery.

Rewiring the primary somatosensory cortex in carpal tunnel syndrome with acupuncture

“…Our previous functional MRI results showed that while ipsilesional S1-hand area is deactivated by local acupuncture, ipsilesional S1-leg area is activated by distal acupuncture (Maeda et al, 2013b). Thus, clinically-relevant fractional anisotropy changes for both local and distal acupuncture were not diffusely distributed throughout S1-adjacent white matter, but were instead localized to areas adjacent to S1 subregions specifically targeted by wrist versus leg acupuncture.…”

Primary somatosensory/motor cortical thickness distinguishes paresthesia-dominant from pain-dominant carpal tunnel syndrome

“…43 Correlation analyses associated cortical thickness and clinical variables (NCV and BCTQ), significant at P # 0.05. In addition, as our previous study directly contrasted structural brain data from subjects with CTS (a subset, N 5 20, of the larger sample, N 5 59, reported herein) vs healthy controls and reported significant gray matter volume differences between patients with CTS and healthy adults, 30 this study did not directly contrast CTS data with healthy controls. In this study, healthy control subject data from significant clusters identified above were used to descriptively aid interpretation of how differences between CTS-pain and CTS-paresthesia cortical thickness relate to cortical thickness measures in age-matched and sex-matched healthy adults.…”

“…We found that reduced gray matter volume within the S1 hand area contralateral to the more affected hand was associated with median nerve sensory velocity. 30 Other studies have also demonstrated reduced gray matter volume in patients with chronic pain 1 and reduced cortical thickness in cases of more severe peripheral deafferentation, such as peripheral nerve transection. 53 However, the association between such structural brain changes and specific symptomatology or peripheral nerve function in patients with chronic neuropathic pain is not well understood.…”

“…56 Another reason for a lack of correlation between electroneurography and symptom report may be due to variable central nervous system plasticity. Recent studies have demonstrated altered functional 10,29,37 and structural 30 properties for CTS in primary somatosensory (S1) cortices of the brain. We found that reduced gray matter volume within the S1 hand area contralateral to the more affected hand was associated with median nerve sensory velocity.…”

Is the Control of Applied Digital Forces During Natural Five-digit Grasping Affected by Carpal Tunnel Syndrome?

“…The patients with CTS had an increased thumb-index finger correlation only during the lowering phase, which may be because the central controller minimized the degree of freedom by augmenting the relative roles of the thumb and index finger [25]. Furthermore, reorganization of the brain structures was found to correlate with the nerve conduction velocity in patients with CTS, and this was thought to be a secondary adaption to the peripheral nerve impairments [31]. However, more research is needed to link the relationships between the motor performance of the distal hand and central neural activities to verify the related control mechanism.…”