Skater's Cramp: A Possible Task-Specific Dystonia in Dutch Ice Skaters.

BACKGROUND

Skater's cramp is an involuntary lower leg movement in skilled speed skaters. We aim to evaluate whether skater's cramp is compatible with task-specific dystonia.

METHODS

A case-control study tested 5 speed skaters exhibiting symptoms of skater's cramp and 5 controls. Affected skaters completed a standardized questionnaire and neurological examination. Video analyses included skating normally, intensely, and with extra mass around the skater's ankles. An Inertial Motion Capturing (IMC) device mounted on both skates provided angular velocity data for both feet.

RESULTS

Median time of onset of skater's cramp occurred after 12 (range 3-22) years of speed skating. Skater's cramp appeared as task specific; its onset was sudden and correlated to stress and aberrant proprioception. Symptoms presented acutely and consistently during skating, unilaterally in 4 and bilaterally in 1 skater. Visually, skater's cramp was an active, patterned, and person-specific jerking of a skater's foot, either exo- or endorotationally. It presented asymmetrically, repeating persistently as the foot neared the end of the swing phase. The skater's affected leg had a longer swing phase (median, 1.37 [interquartile range {IQR}, 0.35]/1.18 [IQR, 0.24] seconds;  < 0.01), a shorter glide phase (median, 1.09 [IQR, 0.25]/1.26 (IQR, 0.29) seconds;  < 0.01), and higher angular velocity during the jerking motion. Symptoms remained constant irrespective of speed or extra mass around the ankle ( > 0.05). No significant differences between legs were detected in the control group.

CONCLUSIONS

Observed clinical, visual, and kinematic data could be an early and tentative indication of task-specific dystonia.