This article includes supplementary video clips, available online at .

mds21645-MDS21645.mpg13401KCase 1There is slowness of finger taps but with no definite fatiguing or decrement. There is obvious wasting of the left first dorsal interosseus.Case 2Segment 1. Repeated finger taps are slow, but with no definite fatiguing or decrement.Segment 2. The patient walks with a narrow-based, stiff gait. There is stooped posture with reduced arm swing bilaterally. There is postural instability on the pull test.

Please note: Wiley Blackwell is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.