Diagnosis
According to the revised fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), Tourette’s may be diagnosed when a person exhibits both multiple motor and one or more vocal tics (although these do not need to be concurrent) over the period of a year, with no more than three consecutive tic-free months. The previous DSM-IV included a requirement for "marked distress or significant impairment in social, occupational or other important areas of functioning", but this requirement was removed in the most recent update of the manual, in recognition that clinicians see patients who meet all the other criteria for Tourette's, but do not have distress or impairment. The onset must have occurred before the age of 18, and cannot be attributed to the "direct physiological effects of a substance or a general medical condition". Hence, other medical conditions that include tics or tic-like movements—such as autism or other causes of tourettism—must be ruled out before conferring a Tourette's diagnosis.
There are no specific medical or screening tests that can be used in diagnosing Tourette's; it is frequently misdiagnosed or underdiagnosed, partly because of the wide expression of severity, ranging from mild (the majority of cases) or moderate, to severe (the rare, but more widely recognized and publicized cases). Coughing, eye blinking and tics that mimic asthma are commonly misdiagnosed.
The diagnosis is made based on observation of the individual's symptoms and family history, and after ruling out secondary causes of tic disorders. In patients with a typical onset and a family history of tics or obsessive–compulsive disorder, a basic physical and neurological examination may be sufficient.
There is no requirement that other comorbid conditions (such as ADHD or OCD) be present, but if a physician believes that there may be another condition present that could explain tics, tests may be ordered as necessary to rule out that condition. An example of this is when diagnostic confusion between tics and seizure activity exists, which would call for an EEG, or if there are symptoms that indicate an MRI to rule out brain abnormalities. TSH levels can be measured to rule out hypothyroidism, which can be a cause of tics. Brain imaging studies are not usually warranted. 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. If a family history of liver disease is present, serum copper and ceruloplasmin levels can rule out Wilson's disease. Most cases are diagnosed by merely observing a history of tics.
Secondary causes of tics (not related to inherited Tourette syndrome) are commonly referred to as tourettism. Dystonias, choreas, other genetic conditions, and secondary causes of tics should be ruled out in the differential diagnosis for Tourette syndrome. Other conditions that may manifest tics or stereotyped movements include developmental disorders, autism spectrum disorders, and stereotypic movement disorder; Sydenham's chorea; idiopathic dystonia; and genetic conditions such as Huntington's disease, neuroacanthocytosis, Hallervorden-Spatz syndrome, Duchenne muscular dystrophy, Wilson's disease, and tuberous sclerosis. Other possibilities include chromosomal disorders such as Down syndrome, Klinefelter syndrome, XYY syndrome and fragile X syndrome. Acquired causes of tics include drug-induced tics, head trauma, encephalitis, stroke, and carbon monoxide poisoning. The symptoms of Lesch-Nyhan syndrome may also be confused with Tourette syndrome. 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.
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