What is synkinesia? what is the relationship between this & adhd?

Involuntary movement: In dyskinesia, when one muscle is moved, there is involuntary movement of another muscle. This sometimes happens in severe bell palsy. Some medicines used for adhd (such as ritalin) list dyskinesia as a side effect.

A neurologic sign: Synkinesia means"move together." normal in the immature nervous system of an infant/young child. When it persists, it's an invaluable diagnostic sign for adhd. No adhd medication causes synkinesia. The answer above is defining dyskinesia, which means "bad movements." here's one of 100's of articles on the subject: dev med child neurol. 2006;48:165–169; doi:10.1017/s001216220600375.