P80-F The spectrum of involuntary movements in patients with motor neuron disease – A cross-sectional study

Abstract

Background We have commonly observed involuntary jerks and tremor in patients with otherwise typical motor neuron disease (MND). We conducted prospective clinical study to explore their prevalence and phenomenology. Materials and methods Seventy-four consecutive patients were clinically examined by movement disorders specialists. Based on regularity and distribution, movements observed at rest were classified as minipolymioclonus (MPMC) or rest thumb tremor (RTT) and movements present during action as action MPMC or action tremor. Results Involuntary movements (IMs) were present in 54 patients (73%). Rest MPMC was present in 26 (35%), RTT in 22 (31%), action MPMC in 22 (30%) and action tremor in 20 patients (27%), with some overlap. Sixteen patients (22%) reported negative impact of IMs on their ability to use hands. Regression model showed that lower distal muscle power and less prominent upper motor neuron (UMN) signs significantly increased the probability of I. Conclusions IMs are common yet largely overlooked feature of MND and may have negative impact on patient’s functional abilities. Lower distal muscle power increased the probability of IMs of fingers and wrist, suggesting that generation of IMs in MND patients is associated with muscle weakness. The presence of UMN signs decreased the probability of IMs, possibly by increasing muscle and joint stiffness. Overall, our findings suggest IMs in MND patients are of peripheral origin. We propose that IMs are caused by activation of enlarged motor units without sufficient previous recruitment of smaller units to smooth their contraction during action and by their spontaneous firing at rest.