Hyperkinetic Movements in Patients With Disease of Motor Neurons and Their Response to Treatment With Nusinersen

Plain-language summary

Hyperkinetic movement disorders in patients with diseases of motor neurons will be studied. Patients with spinal muscular atrophy (SMA) and motor neuron disease patients will be studied. Involuntary movements will be video recorded and accelerometry with electromyography (EMG) will be recorded in a subset of patients. Hyperkinetic involuntary movements studied will be tremor and minipolymyoclonus. Tremor is defined as involuntary, rhythmic, oscillatory movements of a body part, and minipolymyoclonus are intermittent and irregular movements, with amplitudes sufficient to produce visible movements of the joints. Hyperkinetic movement disorders may be of central or peripheral origin and using accelerometry with EMG may help distinguish the two mechanisms. In patients with SMA the investigators will explore the effect of Nusinersen treatment on phenomenology and amplitude of tremor and minipolymyoclonus. Aims: To explore the prevalence and phenomenology of hyperkinetic movement disorders in patients with MND and SMA and to study the underlying pathological mechanisms with the use of accelerometry and EMG. To explore the effect of Nusinersen treatment on phenomenology and amplitude of involuntary movements. Hypotheses: Based on clinical observations the investigators believe it will proven that hyperkinetic movement disorders are common in patients with disease of motor neurons. The investigators hypothesize that hyperkinetic movement disorders in MND and SMA patients are of peripheral origin, being caused by uneven graduation of contraction in the wasted muscles with large motor units being active with no sufficient previous recruitment of small units to smooth contraction of large motor units. If tremor and minipolymyoclonus in SMA are due to the activation of enlarged motor units which are caused by reinnervation of muscle fibers, the treatment with Nusinersen will increase the amplitude of tremor and minipolymyoclonus. Methods: Presence, quality, and regularity of hyperkinetic movement disorders will be defined using clinical examination, accelerometry and EMG. Hyperkinetic movements will be classified as minipolymyoclonus or tremor. In patients with SMA, the measurements will be repeated 6-12 months after initiation of treatment with Nusinersen.

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