Clinical Utility of TMS-EMG Measures

Abstract

Abstract This chapter focuses on the utility of transcranial magnetic stimulation (TMS) for clinical diagnosis and follow-up. We first introduce methods to measure corticospinal excitability, intracortical inhibitory and facilitatory circuits and cortico-cortical connections. We then discuss the use of TMS in several neurological disorders. Central motor conduction time (CMCT) can be used to detect myelopathy and to localize the lesions, while the triple stimulation technique has higher sensitivity. CMCT can also detect upper motor neuron involvement in amyotrophic lateral sclerosis and multiple sclerosis. The ipsilateral silent period and CMCT are helpful for differentiating atypical parkinsonism from Parkinson’s disease. Distinct patterns of cortical excitability findings can be obtained from different genetic forms of hereditary spinocerebellar ataxia. Reduction of short afferent inhibition (SAI) in Alzheimer disease and reduction of short-interval intracortical inhibition (SICI) in fronto-temporal dementia can be reliable indicators to differentiate these two diseases. Patients with diffuse Lewy body dementia and hallucination also have reduced SAI. The results of motor evoked potential measurements in the early stage of stroke are predictive of the long-term motor outcome. SICI, CMCT, and rest motor threshold are useful measurements to monitor extent of clinical disability. We conclude that TMS has clinical diagnostic utility in a broad range of neurological diseases.