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

Abstract

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; P < 0.01), a shorter glide phase (median, 1.09 [IQR, 0.25]/1.26 (IQR, 0.29) seconds; P < 0.01), and higher angular velocity during the jerking motion. Symptoms remained constant irrespective of speed or extra mass around the ankle (P > 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.

Functional Dystonia: Differentiation From Primary Dystonia and Multidisciplinary Treatments

“…First, OD may be mistaken for other conditions such as tremor or Parkinson's disease (65). In addition, particular ODs commonly misdiagnosed as FD include paroxysmal dystonia/dyskinesia (52,53), task-specific dystonias (66,67), dopa-responsive dystonia and other potentially treatable metabolic movement disorders (68), rapid-onset dystoniaparkinsonism (69), and acute drug-induced and tardive dystonias (57). There are also the various non-FND pseudodystonias (e.g., abnormal postures related to atlanto-axial subluxation, compensatory movements after injury, or similarities in presentation in pathological muscle stiffness/myotonia, etc.…”

Sports-Related Dystonia

“…In addition to golf and running, dystonia has been reported in other sports. Those sports include tennis [ 48 ], petanque [ 49 ], pistol shooting [ 50 ], table tennis [ 51 52 ], billiards [ 53 54 ], baseball [ 55 ], and ice-skating [ 56 ]. There is a limited number of articles on dystonia or other movement disorders in these sports, probably because of the rarity of the condition or probably because it is underrecognized or underdiagnosed.…”

“…Yips in the Dutch ice speed skaters was reported in a series of five subjects by a group of authors led by Nijenhuis, a former Olympic speed skater who was affected by yips [ 56 ]. In the Netherlands, this skaters’ cramp is known as “zwabbervoet” (English- mop foot) and it has hampered the professional career of several Dutch skaters.…”

“…The skaters usually describe this as a feeling of reduced control in the affected foot/leg which occurs only while speeding and inline skating. Visually it may manifest as a twitch or jerky spasm when the skate is suspended in the air and before it is placed on the ice (in the swing phase) [ 56 ]. In the above-referenced study, three out of the five skaters experienced extreme stress prior to the onset of the yips.…”