dyskinesia

Parkinson's disease is known for movement that is too little: slowness, stiffness and tremor. Dyskinesia is the opposite problem, movement that happens unbidden. The National Institute of Neurological Disorders and Stroke describes it as unwanted movements such as twisting and writhing, and lists it among the effects that Parkinson's medicines themselves can cause, alongside hallucinations and strong urges to repeat certain behaviours. The same institute notes that over time the medicines' effects become less predictable and side effects may develop.

Because of this, trials of Parkinson's drugs do not simply count the hours a person can move. The TEMPO-3 trial of tavapadon, reported in JAMA Neurology, took as its main measure good on-time, the daily hours of good mobility without troublesome dyskinesia, and counted dyskinesia itself among the drug's most common adverse events, reported by 10 percent of the people taking it. The word separates drug-induced movement from the tremor of the disease: a tremor is a rhythmic back-and-forth shaking, most obvious when the hand is at rest, while dyskinesia is the twisting and writhing that treatment can bring.