Clinical features can often distinguish between dystonia, spasticity and rigidity.
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Parameter
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Dystonia
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Rigidity
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Spasticity
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muscle findings
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intermittent or sustained muscular contractions
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not affected by speed or posture
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resistance velocity dependent
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fixed posture
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yes
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no
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may be present in severe cases
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Spasticity findings (absent in dystonia and rigidity):
(1) increasing speed of passive movement increases resistance
(2) rapid reversal of direction has a delayed effect on resistance
Dystonia findings (absent or minimal in rigidity and spasticity):
(1) voluntary activity affects the pattern of activated muscles
(2) emotional state affects the pattern of activated muscles
