Tourette Syndrome is typically not diagnosed until after a year of a patient exhibiting both multiple motor tics and one or more vocal tics. The patient cannot have had more than three consecutive months without experiencing tics. For a diagnosis to occur, the patient must also have experienced the onset of tics before age 18.
Another requirement for diagnosis is that the symptoms cannot be attributed to the physiological effects of a substance or other medical condition. Other medical conditions that involve tics or disorders such as autism must also be ruled out before Tourette's can be diagnosed.
Tourette's can be difficult to diagnose. Many mild cases are never diagnosed, as they may not be severe enough for medical attention or may be considered just part of a child's normal developmental phase. Also, some symptoms of the tics involved with Tourette's such as eye blinking may be associated with other disorders. There are also no specific medical or screening tests used to diagnose Tourette's. However, physical and neurological examinations may be used for a diagnosis.
Family history is a factor in diagnosis. Children of parents with Tourette's are more likely to have the disorder. In fact, some parents become aware that they too had tics as a child after bringing their child in to a physician for an evaluation.
However, other secondary causes of tics must be ruled out before a diagnosis occurs. People with Tourette's may also be diagnosed with Attention–Deficit Hyperactivity Disorder or Obsessive–Compulsive Disorder. Learning disabilities and sleep disorders are also associated with Tourette's.
There can be confusion between tics and seizures. When this is the case, the physician can request an EEG, CT or an MRI to rule out brain abnormalities. Samples from the body may also be taken to rule out hypothyroidism, which can be a cause of tics. A urine test may also be taken to rule out the use of drugs such as stimulants.