Extreme hypertonicity is referred to as which term?

• A. Rigidity
• B. Dystonia
• C. Myoclonus
• D. Spasticity

Answer: (D)

Extreme hypertonicity is best described as spasticity, a form of upper motor neuron–related hypertonia. Spasticity is defined by a velocity-dependent increase in resistance to passive stretch—the faster you move the limb, the more resistance you feel. This happens because the stretch reflex is exaggerated when the muscle is being moved quickly, and it often comes with other signs like hyperreflexia and sometimes clonus. This distinguishes spasticity from rigidity, which is a constant resistance not tied to movement speed and is typical of Parkinsonian conditions. Dystonia involves sustained or repetitive muscle contractions that produce abnormal postures, not just heightened tone, and myoclonus refers to brief, shock-like jerks rather than sustained increased tone. Understanding that spasticity is velocity-dependent helps explain why passive movement speed matters and guides treatments that target the nerve pathways and reflexes, such as certain medications or focal interventions combined with therapy.