Tourette Syndrome (TS) is an often-misunderstood neuropsychiatric disorder that occurs more often in males and affects four to five children per 10,000 (although some studies report rates as high as 3% of the population). Because most cases of TS are mild and do not come to medical attention, or are often unrecognized and misdiagnosed, prevalence rates have been difficult to determine.
Diagnosis and Classification
Tics are defined as sudden, repetitive, stereotyped movements and vocalizations and are generally classified as simple (those that are rapid and appear to have no purpose) or complex (slower, more orchestrated, and appearing as if they might have some purpose). Diagnoses of tic disorders are based on history and clinical presentation; there is no diagnostic test. According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV), a diagnosis of Chronic Motor Tic Disorder is made if the individual has had motor tics for over a period of one year. Likewise, the diagnosis Chronic Vocal Tic Disorder is made if vocal tics have been present for at least one year. If motor tics and at least one vocal tic have been present for at least one year, the diagnosis of Tourette disorder is given. The period of one year is used as a demarcation to avoid diagnosing children who have transient tics, as is the case for approximately 15% of children. The onset of tic disorders is before age 18.
Typically, tics begin around the age of 5 to 7 years, although earlier onset can occur. Motor tics generally appear prior to the onset of vocal tics. The most common initial presentation of a motor tic is eye blinking followed by other facial movements, which include eye movements (gazing up, down, or sideways), nose wrinkling, mouth movements, jaw stretching, and facial grimacing. Tics generally progress in a head-downward trajectory, beginning in the facial area and gradually moving downward to affect the neck, shoulders, trunk and limbs. Vocal tics most commonly begin as simple tics, such as sniffing, snorting, throat clearing and coughing. From there, they may become more complex and include emphasis on certain consonants or syllables, repetition of syllables and words, changes in pitch and volume, repeating self or others, and blurting out inappropriate comments, including coprolalia. Contrary to what the media often portray, coprolalia is actually quite rare, affecting approximately 10–15% of people with TS. It is also important to note that not everyone with TS will have this presentation. In relatively mild cases of TS the individual may only have some facial tics and simple vocal tics that do not progress to a more moderate or severe case.
Individual tics are usually brief in duration but often occur in clusters or bouts so that a person may experience several tics that are followed by a brief “quiet” period followed by another bout of tics. This same pattern occurs regardless of the period observed, whether it is over hours, days, weeks or months, producing the characteristic waxing and waning of tics. Recent research has shown that tics generally seem to cycle through waxing and waning periods approximately every three months.
Tics tend to increase in intensity, frequency and complexity throughout childhood and into puberty. For most children, the intensity, frequency and complexity will begin to decline gradually around puberty so that by the time adulthood is reached, the tics are either very mild or have remitted in approximately 65% of people who had tics as children.
Tic disorders are genetically mediated; recent research indicates that they most likely are not due to a single gene but rather to the confluence of various environmental factors in combination with certain candidate genes. Whatever the mode of transmission may be there is evidence for the involvement of specific cortico-striato-thalamic-cortical circuits in the brain. These circuits convey information in a highly specific manner through the basal ganglia and modulate the neuronal activity of several brain systems related to the control (initiation and monitoring vs. inhibition) of different aspects of psychomotor behavior. The neurochemical systems that regulate the activity of these circuits involve dopamine, serotonin and norepinephrine.