Which movement disorder is irregular, shocklike, can be generalized or focal, is not from the basal ganglia, and can be action- or stimulus-sensitive?

• A. Dystonia
• B. Akathisia
• C. Tremor
• D. Myoclonus

Answer: (D)

Myoclonus is defined by sudden, brief, shock-like jerks of a muscle or group of muscles. These jerks are often irregular, can appear as generalized movements or be focal to a single region, and they can be triggered or amplified by action or external stimuli (stimulus-sensitive). Importantly, myoclonus is not typically rooted in basal ganglia dysfunction; it more often arises from cortical, brainstem, or spinal mechanisms. This combination—irregular, shocklike jerks that can spread or stay focal, plus sensitivity to action or stimuli and a non-basal-ganglia origin—best fits myoclonus. By contrast, dystonia involves sustained or intermittent abnormal postures from excessive muscle contractions, akathisia is marked by inner restlessness and urge to move, and tremor is a rhythmic oscillation, none of which captures the described shocklike, irregular jerks.