Tourette syndrome. Phenomenology and classification of tics.

Motor and phonic tics represent the clinic hallmark of Tourette syndrome. Since there is no diagnostic test for tics, the clinical recognition of phenomenology is essential for proper diagnosis. Some, and possibly most, motor tics are preceded by a premonitory urge or sensation that is relieved by the execution of the tic and thus can be difficult to differentiate from compulsions, hence the term compulsive tic. In the schema of categorization of movements, most tics can be classified as either unvoluntaryin response to an inner sensory stimulus or to an unwanted feeling compulsionor involuntarytics that are usually suppressible. Further studies are needed to elucidate the clinical, anatomical, and physiologic substrates for the different forms of tics. Finally, the relationship between tics and comorbid conditions, such as obsessive-compulsive disorder and attention deficit with hyperactivity needs to be further explored.