Clinical spreading of muscle weakness in amyotrophic lateral sclerosis (ALS): a study in 910 patients

Background Neuroanatomical staging of sporadic amyotrophic lateral sclerosis (ALS) indicates that neurodegeneration may spread corticofugally.

Methods We conducted an observational study to define the initial sites of disease onset and the clinical progression (‘spreading patterns’) of motor deficits in a cohort of 910 ALS patients in Germany.

Results Mean age of ALS onset was 59.0 ± 12.6 years for males and 61.2 ± 10.5 years for females, the mean ALSFRS-R was 35.1 ± 9.2, and 7.7% of the cohort reported a family history.

Onset of motor symptoms was bulbar/upper limb in 26.8%/35.9%, the right arm initially being slightly more often affected than the left (18.5% vs.16.3%).

Testing on concordance of handedness and onset in the dominant arm did not reach significance.

Lower limb onset was observed in 37.3%.

Unilateral limb onset patients reported horizontal spreading about three times more often than vertical spreading.

71/244 bulbar onset patients reported spreading pattern to the legs, and 17/339 lumbar onset patients reported spreading secondarily to the bulbar region.

Discussion Our results indicate that, although the phenotype of so-called ‘spinal’ or ‘intraspinal’ spreading predominated, we also observed an additional clinical spreading pattern: 29.1% of patients with bulbar onset experienced spreading clinically to the legs (vice versa in 5.0% of lumbar onset patients).

For obvious neuroanatomical reasons, this pattern hardly can be explained solely by a ‘spinal’ or an ‘intraspinal’ pattern of spreading.

Instead, these findings complement insights from previous clinical and clinicopathological studies supporting a cortical initiation of ALS.