Abstract
ObjectiveCarpal 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 matter (GM) and white matter (WM) and whether such plasticity is linked to altered median nerve function in CTS.MethodsWe 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.ResultsFor 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.ConclusionsOur 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.
Highlights
Carpal tunnel syndrome (CTS) is a common neuropathy associated with median nerve conduction block, as well as pain, numbness and paresthesia in the median nerve innervated territory of the affected hand
As gray matter (GM) reduction in primary somatosensory cortex (S1) was associated with decreased impulse conduction along the median nerve, similar to what we found for functional brain reorganization in CTS (Napadow et al, 2006, 2007), we propose that cortical reorganization in CTS extends to structural change, triggered by chronically altered peripheral afference
We further found that greater fractional anisotropy (FA) and lower RD in a saddle region of the cortico-cortical U-fiber white matter (WM) tract connecting S1 to primary motor cortex (M1) was correlated with nerve conduction velocity (NCV)
Summary
Carpal tunnel syndrome (CTS) is a common neuropathy associated with median nerve conduction block, as well as pain, numbness and paresthesia in the median nerve innervated territory of the affected hand. In addition to the peripheral sensorimotor manifestations of CTS, cortical digit representations in the brain display expansion, amplification, and/or shifted locus in the primary somatosensory cortex (S1), as evaluated by both fMRI (Napadow et al, 2006, 2007; Zanette et al, 2006) and MEG (Dhond et al, 2012; Tecchio et al, 2002). These studies suggest that the function of the entire hierarchy of the somatosensory system from the peripheral to the central sites may be altered in CTS. Maeda et al / NeuroImage: Clinical 2 (2013) 313–319 brain gray matter (GM) and white matter (WM) and, if so, how it is associated with altered peripheral nerve function and symptomatology
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