Sticking with spasm (3)
I believe the answer is:
tic
'spasm' is the definition.
(I know that tic is a type of twitch)
'sticking with' is the wordplay.
'with' indicates a hidden word.
'TIC' is hidden within 'sticking'.
(Other definitions for tic that I've seen before include "Involuntary muscular spasm" , "Muscle twitch" , "Jerky movement" , "Minor muscle spasm" , "Convulsive spasm" .)