This criteria is taken from the Diagnostic and Statistical Manual (DSM) of the American Psychiatric Association. Changes to this criteria have taken place in the past and will likely take place in the future.
The term “involuntary” used to describe TS tics is a source of confusion since it is known that most individuals with TS do have some control over their symptoms. What is not recognized is that the control, which can be exerted from seconds to hours at a time, may merely postpone more severe outbursts of symptoms. Some tics are experienced as an irresistible urge and must eventually be expressed. Individuals with TS often seek a secluded or safe place to release their symptoms after delaying them in school or at work. Thus, they may be at their worst at home. Typically, tics increase as a result of tension or stress (but are not caused by stress) and decrease with concentration on an absorbing task.
Some diagnosing professionals will strictly adhere to the DSM criteria while others will allow for some variance in the symptoms.
In one reported case a 29 year old woman suddenly began displaying classic symptoms of TS where no symptoms had previously been evident. During discussions with her mother, the woman recalled having had TS-like or tic-like behaviours when she was a teen. In this case, the history allows the DSM criteria to be met, however, had the mother not been available, the criteria would not have been met.
In a 2007 presentation at the TSFC’s annual conference a speaker presented the case that sounds, either vocal or phonic, were created by muscle movements and therefore all tics should be considered “motor.”