Background: Minipolymyoclonus and tremor are frequently mentioned as part of the clinical picture of spinal muscular atrophy, but the precise mechanism of the occurrence of tremor and minipolymyoclonus in these patients remains unknown. In the 1970s it was suggested minipolymyoclonus and tremor are caused by reinnervation that follows denervation of muscle fibers in neuropathies. The investigators are not aware of any later or more systematic study on the frequency of minipolymyoclonus and tremor occurrence in SMA patients or its evolution during the disease course. Nusinersen, an antisense oligonucleotide, is a medicine registered for treating SMA. Nusinersen increases the production of the functional survival motor neuron protein by regulating gene expression and thus slows down or stops alpha-motor neuron degradation. MND is considered a disease of upper and lower motor neuron and movement disorders are not considered part of its typical clinical picture. Movement disorders are only reported in MND in association with extrapyramidal or cerebellar degeneration or dysfunction. Contrary to this, the investigators have encountered anecdotal evidence from a number of patients with otherwise typical MND who manifested involuntary jerks and tremor.
Aims: To explore the prevalence and phenomenology of hyperkinetic movement disorders in patients with SMA and MND, to explore the effect of Nusinersen treatment on phenomenology and amplitude of tremor and minipolymyoclonus, and to elucidate the underlying pathological mechanisms by using accelerometry and EMG.
Patients and inclusion/exclusion criteria: All genetically proven SMA patients who will be treated with Nusinersen and consecutive patients followed in MND outpatient clinic will be recruited. Patients with SMA type I, II, III, and IV and patients with ''clinically definite ALS'' or ''clinically probable ALS'' or ''clinically probable ALS - laboratory supported'' according to the revised El Escorial diagnostic criteria or with the diagnosis of PMA or PLS will be included. There will be no exclusion criteria.
Study protocol: All patients will be clinically examined and video-recorded. SMA patients will be examined and video-recorded for the second time 6-12 months after initiation of treatment with Nusinersen. The presence, quality, and regularity of involuntary movements will be evaluated while subjects will be sitting in a chair with hands resting in their lap (usual posture when examining rest tremor), during forward horizontal reach posture, and during finger to nose task. Based on regularity and distribution, hyperkinetic movements will be classified as minipolymyoclonus (MPMC) or tremor. Accelerometry with EMG will be recorded in a subset of patients with hyperkinetic movements.
Methods:
Accelerometry with electromyography: With accelerometry tremor (frequency and amplitude) in the subjects will be objectively evaluated. A triaxle accelerometer will be attached to the 3rd metacarpal bone bilaterally. Simultaneously EMG will be recorded. Bipolar Ag / AgCl surface EMG electrodes will be placed over the flexor carpi radialis and the extensor carpi radialis muscle bilaterally. Electromyography and accelerometry will be recorded while subjects will be sitting in an armchair/wheelchair or lying in a hospital bed (a) at rest position (b) with arms outstretched (postural condition) (c) at the postural condition with 500 g mass attached to the hand (weight loading) and (d) while performing a goal-directed task (action).
Statistical analysis: Clinical measures before and after Nusinersen treatment will be compared using two-related-samples T-test or repeated-measures ANOVA. To assess possible causative mechanisms (disease factors) that determine the presence of involuntary movements, separate multilevel binary logistic analyses will be performed.
