Methods of detecting lesions of upper motor neuron in amyotrophic lateral sclerosis using transcranial magnetic stimulation

Introduction. Coexistent involvement of upper and lower motor neurons is a characteristic feature of amyotrophyc lateral syndrome (ALS) necessary for the diagnosis. Diagnosis of upper motor neuron involvement in ALS is based solely on clinical features, which may not be detected at the disease onset and in rare forms manifesting clinically as the local lower motor neuron syndrome (LLMNS). The main method of assessment of the functional state of the upper motor neuron in ALS is transcranial magnetic stimulation (TMS). It allows assessing the excitability of motor cortex, corticospinal path function, and mapping of cortical representation of the muscles. In patients with ALS changes of various indicators demonstrating hyperexcitability as well as degenerative lesions of the motor cortex and the corticospinal tracts are recorded on TMS. Objective: to discuss changes in the TMS in patients with LAS, pathophysiological mechanisms of their formation and possible diagnostic value. Results. In 22 patients with LLMNS, navigation TMS revealed disturbances of intracortical suppression on paired stimulation with recording period of silence, increase of motor threshold in dominant hemisphere, decrease of the weighted square and reorganization of cortical representations of the hand muscles. Conclusion. The data obtained allow to consider navigation TMS as a promising technology for identifying upper motor neuron involvement in patients with ALS.