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Session: Neurophysiology & Sleep
Session starts: Thursday 26 January, 10:30
Presentation starts: 11:45
Room: Room 530

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Boudewijn T.H.M. Sleutjes (Department of Neurology, Brain Centre Utrecht, University Medical Centre Utrecht)
Diederik J.L. Stikvoort Garcia (Department of Neurology, Brain Centre Utrecht, University Medical Centre Utrecht)
H. Stephan Goedee (Department of Neurology, Brain Centre Utrecht, University Medical Centre Utrecht)
Leonard H. van den Berg (Department of Neurology, Brain Centre Utrecht, University Medical Centre Utrecht)

Abstract:
Surface-electromyography (EMG) methods have been shown to provide insights on disease pathology of motor neuron diseases (MND) by detecting two prominent mechanisms: loss of motor units (MUs) and enlarged MUs due to collateral reinnervation (i.e. denervated muscle fibers become reinnervated by still functioning peripheral motor neurons). Due to collateral reinnervation muscle strength may for a certain time be relatively maintained. The interaction of these two mechanisms may vary greatly between patients. By simulating their interaction, we aim to provide insights into their impact on the sensitivity of surface-EMG methods to monitor disease progression in MND. Therefore, we developed a muscle model to simulate progressive MU loss and enlarged MUs due to reinnervation. High-density surface-EMG recorded single MU potentials (MUPs) formed the basic building blocks of the model. From the baseline MU pool innervating a muscle, progressive MU loss was simulated by the one-by-one removal of MUs. These removed MUs underwent reinnervation with scenarios varying from 0% to 100% by neighbouring MUPs depending on the overlap in their topographical fingerprints. We tailored the model to generate compound muscle action potential (CMAP) scans, which is a promising surface-EMG method for monitoring patients with MND. This allowed us to compare simulated and recorded CMAP scans in healthy controls and patients with MND. Simulated baseline maximum CMAP showed values up to 12 mV. During progressive MU loss and reinnervation, the CMAP scan pattern showed a clear transition from a smooth sigmoidal towards a more discrete stepwise pattern, which matched well with experimental observations. Reinnervation was successfully reflected by increases in MU size resulting in enlarged MUs up to 2 mV when only a few MUs are left, which are sizes also occasionally observed during experiments. The muscle model was able to capture on average the pathological MU characteristics observed in patients with MND. Further refinements are possible towards more patient-specific patterns over time. The model could be used as surrogate reference to compare MU number estimate (MUNE) methods without posing unnecessary burden to patients. This may also aid in designing more sensitive biomarkers for monitoring disease progression of MND.