A tic is a sudden and repetitive motor movement or vocalization that is not rhythmic and involves discrete muscle groups.
[4] Phonic tics are involuntary sounds produced by moving air through the nose, mouth, or throat.
[4] Simple motor tics are typically sudden, brief, meaningless movements that usually involve only one group of muscles, such as eye blinking, head jerking, or shoulder shrugging.
[11] Tics are described as semi-voluntary or unvoluntary,[12] because they are not strictly involuntary—they may be experienced as a voluntary response to a premonitory urge (a sensory phenomenon that is an inner sensation of mounting tension).
[14][15][16] Neurologist and writer Oliver Sacks described a physician with severe Tourette syndrome (Canadian Mort Doran, M.D., a pilot and surgeon in real life, although a pseudonym was used in the book), whose tics remitted almost completely while he was performing surgery.
[17][18] Immediately preceding tic onset, most individuals are aware of an urge[19] that is similar to the need to yawn, sneeze, blink, or scratch an itch.
Individuals describe the need to tic as a buildup of tension[20] that they consciously choose to release, as if they "had to do it".
[24][25][26][27] Dystonias, paroxysmal dyskinesias, chorea, other genetic conditions, and secondary causes of tics should be ruled out in the differential diagnosis.
[28][32] Most of these conditions are rarer than tic disorders, and a thorough history and examination may be enough to rule them out, without medical or screening tests.
[34] In teenagers and adults presenting with a sudden onset of tics and other behavioral symptoms, a urine drug screen for cocaine and stimulants might be necessary.