TMS and the Neurology of Multiple Sclerosis
Since the first clinical studies of TMS, prolongation of central motor conduction time (CMCT) has been reported as a finding in MS (Barker et al. 1986, Hess et al. 1986). TMS has been frequently used to investigate altered hemispheric and inter-hemispheric connectivity in MS.
Monitoring The Disease
MEP abnormalities are usually present in muscles that show clinical weakness and are also common when upper motor neuron signs are present, but only occasionally in extremities with normal clinical examination. MEP recordings therefore are more helpful in confirming abnormalities in patients with clinically equivocal motor findings than establishing motor lesions in patients with normal examination (Oxford Handbook).
TMS is used to monitor motor disability in patients with MS, owing to the frequency of lesions in cortico-spinal pathways and the significant correlation observed between the abnormalities in CMCT and the degree of motor disability (Sahota et al. 2005). The monitoring of MS by TMS has been advancing rapidly in sophistication and popularity in recent years.
As motor tasks are associated with increased activation of ipsilateral motor cortical areas in MS patients, Zeller et al (2011) recently examined the role of two ipsilateral motor areas during performance of a simple motor task using TMS. They determined that recruitment of ipsilateral motor areas may be a functionally relevant, yet limited adaptive response to chronic brain injury in MS patients.
Inflammation triggers secondary neurodegeneration in multiple sclerosis (MS). Rossi et al (2011) determined via TMS that GABAA-mediated cortical inhibition was more pronounced in patients with high IL-13 levels in the CSF, as expected for a neuroprotective, anti-excitotoxic effect, supporting the hypothesis that IL-13 is involved in the modulation of neuronal integrity and synaptic function in patients with MS.
Modulating The Disease
TMS is also being exploited in the development of sensitive, reliable and valid biomarkers to measure neurodegeneration in patients. The generation of such biomarkers is hoped will drastically increase the chances of developing a clinically effective treatment (Ziemann et al 2011).
- Rossi et al., Multiple Sclerosis Journal, 2011.
- Sahota et al., Neurology India, 2005.
- Zeller et al., J Neurol Neurosurg Psychiatry, 2011.
- Ziemann et al., Progress in Neurobiology, 2011.