Assessing Motor Neuron Disease Mechanisms by Threshold Tracking Transcranial Magnetic Stimulation and Magnetic Resonance Spectroscopy

Amyotrophic Lateral Sclerosis (ALS) is a motor neuron disease, which cases the death of neurons controlling the voluntary muscles. The death of motor neurons leads eventually to muscle weakness and muscle atrophy and as a consequence thereof, ALS patients die in average within three years after symptom onset due to respiratory failure. No cure for ALS is currently known, and the medical diagnosis and clinical treatment are impeded by the lack of reliable diagnostic tools for objective disease assessment, and by the limited insight in disease pathophysiology since the underlying disease mechanisms still have not been fully elucidated. An unbalance in the concentrations of GABA and glutamate, the most important inhibitory and excitatory brain metabolites, is suggested to play a role in the disease mechanisms of ALS. By applying Magnetic Resonance Spectroscopy (MRS), a magnetic resonance method which allows for quantification of brain metabolites, GABA and glutamate concentration can be quantified and thus hopefully elucidate their role in ALS disease mechanism. Threshold Tracking Transcranial Magnetic Stimulation (TT-TMS) studies carried out by a single research group have demonstrated cortical hyperexcitability (a physiology state in which neurons in the cerebral cortex are easier activated) as an early feature in ALS patients. For this reason, TT-TMS was suggested as a biomarker of ALS by the research group. However, to be able to suggest a test as a biomarker, one must show the test is reliable and reproducible. The objectives of this study are therefore: to explore the pathophysiology of ALS by investigating the interaction between neuronal networks as assessed by TT-TMS and conventional TMS and MRS, and to investigate the reliability and reproducibility of TT-TMS. The aim is to examine the utility of TT-TMS and MRS as diagnostic tools for objective detection of ALS in the early disease stage. The study will include 60 participants in total, subdivided into t