Tic disorders, which are characterized by involuntary movements, vocalizations, or gestures, usually appear in early childhood. For the most part, these tics typically disappear with maturity. However, this isn’t always the case. In fact, those enduring for 12 months or more are defined as chronic as outlined in the Diagnostic and Statistical Manual of Mental Disorders (DSM).
The DSM further defines the different types of tic disorders according to their frequency and length of expression. Other criteria used to classify tic disorders include the age of onset, as well as the route to manifestation (i.e., vocal or motor). Other criteria help to isolate outside factors that may contribute to tic disorders, such as emotional stress, physical trauma, or medications.
Transient tic disorders are by far the most common type and can affect up to 20 percent of children under the age of 18 years. As the name implies, these types of tics are usually of short duration and diminish over time without medical intervention. Transient tics can also appear in a great variety of ways. For instance, transient phonic tic disorders may involve repetitive throat clearing or grunting, while transient motor tics may appear as constant blinking of the eyes or coordinated finger movements. Transient tic disorders also commonly involve changing behaviors, often causing them to be dismissed as nervous habits.
A chronic tic disorder is defined as being either vocal or motor and lasting for more than a year, sometimes for several years. Unlike transient tics, the repetitive or involuntary behavior remains consistent throughout the duration of the disorder. In addition, chronic tic disorders commonly involve multiple behaviors of the same origin, but are never both motor and vocal.
There is also a distinction made between simple tics and complex tics. For example, with simple motor tics, the involuntary movement is sudden and fleeting. In contrast, the movement made in complex motor tics seems more deliberate, even appearing to be made consciously. Likewise, simple vocal tics involve making sounds or utterances at random, while complex vocal tics are characterized by real words or phrases.
There are additional classifications of simple and complex tic disorders. A vocal tic that includes suddenly blurting out obscenities is known as coprolalia, while the compulsion to repeat the same words over and over is called palilalia. In addition, “parroting” the words spoken by others is known as echolalia. Similarly, copropraxia is the term for making involuntary obscene gestures, and echopraxia means to mimic the gestures of others.
Tourette’s syndrome, also known as Tourette’s disorder, is the most severe form of tic disorder and is marked by both vocal and motor tics. The frequency and degree to which these tics take form varies with each individual. There is some evidence to suggest that Tourette’s may be genetically inherited via bilineal transmission, meaning derived from both parents. Specifically, researchers have found a strong association between Tourette’s in children who also have fathers that exhibited tics in childhood and mothers with a history of obsessive-compulsive behaviors.
