Mirror Movements in Amyotrophic Lateral Sclerosis

Objective: It was the aim of the study to investigate the occurrence of mirror movements (MM) and callosal dysfunction in amyotrophic lateral sclerosis (ALS) which have not been studied systematically till yet.

Methods: 26 ALS patients (9 women, mean age of 62.6±8.8 y.) were studied by investigation of MM and transcranial magnetic stimulation (TMS) with evaluation of the ipsilateral silent period (iSP). The revised ALS Functional Rating Scale (ALFRS-R) was assessed and MM were quantified by a score from 0 to 4 in an intentional unimanual repetitive finger-tapping and -sequencing task while having the opposite arm resting.

Results: 10 patients had suspected, 7 patients possible, 4 patients probable and 5 patients definite ALS according to the El Escorial criteria. Mean disease duration was 1±0.7 years. Disease duration did not differ between the two groups (MM- vs. Non-MM- group, 1.3±1.4 vs. 1.4±1.1, resp.; p=0.955). Mean ALSFRS-R was 35±12. There was no correlation between ALSFRS-R and classification according to the El Escorial criteria. MM were observed in ten ALS patients (38.5%). Mean scoring of MM was 2.2±0.9, indicating a severity of slight but unsustained repetitive movements or stronger, but briefer one. There was a significant correlation between the ALSFRS-R and occurrence of MM (Spearman-Rho correlation coefficient [SRCC] –0.315; p=0.044). MM patients had pathological TI at least in one hemisphere. 6 patients with MM did show an ALSFRS-R score higher than 40 (maximum 48). 18 patients showed a pathological iSP (12 without prolongation of the central motor conduction time). 16 of 36 hemispheres displayed a loss of iSP, whereas 11 showed a prolongation of its latency (mean prolongation + 3.8ms). Mean iSP latency was significantly prolonged in the MM group compared to the Non MM group (46.2±5.6/43.9±3.4 and 40.3±5.1/41±4.1, resp.; p=0.012 and p=0.004, resp.). There was a correlation between pathological inhibition parameters and ALSFRS-R (SRCC –0.443 and –0.543, resp.; p=0.034 and 0.007, resp.).

Conclusions: MM in association of affection of transcallosal dysfuntion seem to be relatively common. Affection of the transcallosal fiber tracts even in patients with high ALSRS-R scores, e.g. a better clinical state, is pointing at an involvement of these pathways early in the course of the disease. Concerning TMS and fMRI studies, callosal involvement seems to be a consistent feature of ALS.