minutes), constant repetitive fixed form and location, exacer bation when engrossed in ac-
tivities, lack of a premonitory urge, and ce ssation with distraction (e.g., name called or
touched). Chorea  represents rapid, random, continua l, abrupt, irregular, unpredictable,
nonstereotyped actions that are usually bilatera l and affect all parts of the body (i.e., face,
trunk, and limbs). The timing, direction, and dist ribution of movements vary from mo-
ment to moment, and movements usually worsen during attempted voluntary action. Dys-
tonia  is the simultaneous sustained contracture of both agonist and antagonist muscles,
resulting in a distorted posture or movement of parts of the bo dy. Dystonic postures are of-
ten triggered by attempts at voluntary movements and are not seen during sleep.
Substance-induced and paroxysmal dyskinesias. Paroxysmal dyskinesias usually oc-
cur as dystonic or choreoathetoid movement s that are precipitated by voluntary move-
ment or exertion and less commonly arise from normal background activity.
Myoclonus. Myoclonus is characterized by a sudden unidirectional movement that is
often nonrhythmic. It may be worsened by movement and occur du ring sleep. Myoclonus
is differentiated from tics by its rapidity, la ck of suppressibility, and absence of a premon-
itory urge.
Obsessive-compulsive and related disorders. Differentiating obsessive-compulsive
behaviors from tics may be difficult. Clues fa voring an obsessive-compulsive behavior in-
clude a cognitive-based drive (e.g., fear of co ntamination) and the n eed to perform the ac-