Non-invasive neuroimaging approaches in managing carpal tunnel syndrome

Abstract

Carpal tunnel syndrome (CTS) is literally a peripheral nerve entrapment neuropathy. Alternatively, it can be considered as a chronic pain disorder. The primary affected nerve structure is the myelin sheath of the median nerve at carpal tunnel, associated with axonal degeneration following the progressive demyelination process. Recent studies also revealed neural plastic changes occurred secondary to the sustained symptomatology. Neuroimaging approaches have been applied in various aspects of CTS studies. Among those neuroimaging studies focused on the affected wrist, ultrasound has been universally agreed as a reliable assessment tool, which was applied in diagnostic, prognostic and clinical aspects via providing anatomical information of the affected median nerve. However, the current diagnostic regime cannot clearly discriminate the associated axonal degeneration. Besides, tremendous controversies still remain regarding its prognostic utilities in conservative studies as well as its disputed clinical role in describing the symptomatology. On the other hand, regarding the secondary neural plastic changes following CTS, task-based neuroimaging approaches such as functional magnetic resonance imaging (fMRI) were mainly utilized. However, considering its technical pitfalls on studying the chronic pain disorder, it is agreed that pseudo-continuous arterial spin labelling (pCASL) technique can be more appropriate in reflecting neuronal alternation in the peripheral nerve entrapment ascribed to its higher spatial resolution and ability to directly quantify the neuronal activities. Therefore, this two-phase study was proposed to refine the use of non-invasive neuroimaging approaches at both primary injured (Phase I) and secondary neural plastic sites (Phase II). In phase I studies, the application of ultrasound in diagnostic, prognostic and clinical aspects were discussed. Whereas in phase II, the activated individual brain regions following the symptoms, with its neural plastic pattern were delineated using pCASL technique. The overall goal is to advance CTS management via successive studies in these two phases. The result in Phase I revealed ultrasound can help to screen the axonal degeneration, predict therapeutic outcome after conservative management and reflect the degree of impaired functionality in CTS. Whereas in Phase II, increased neuronal activities at subcortical brain regions were found, associated with sustained symptoms and altered neurophysiological performance, indicating chronic symptoms internalized and emotionalized. The overall findings highlighted the significance of early identification of associated axonal degeneration, thus calling for addressing the ignored aspects to block the chronification of pain.