Tourette Syndrome and Other Tic Disorders 137Epidemiology
Most estimates of the prevalence of Tourette syndrome are in the region
of 3–10 per 10,000 children and adolescents – but some estimates are
much higher. The ratio of males to females is at least 3:1. Chronic motor
tics are probably at least three times commoner than Tourette syndrome.
Transient tics are much commoner still, reportedly affecting up to 4–16%
of young people at some stage (but these rates are based on parent reports
and may be overestimates due to misidentification).
Characteristic features
The average age of onset of motor tics is 7 years, with onset being rare
before two or after 15. The commonest motor tics are simple motor tics
involving eyes, face, head or neck. Complex motor tics are rarer and
emerge later. Phonic tics usually start a year or two after motor tics.
Simple phonic tics are commoner than complex phonic tics. Complex
phonic tics involving obscene speech (coprolalia) only occur in a minority,
starting about four to eight years after onset. It is a mistake, therefore,
to rule out the diagnosis of Tourette syndrome on the basis that the
famous symptom of coprolalia is absent. Echoed speech (echolalia), echoed
actions (echopraxia), and obscene actions or gestures (copropraxia) may
also occur.
Associated features
1 Obsessive-compulsive symptoms (sometimes amounting to an obsessive
compulsive disorder (OCD)) occur in a third to two-thirds of individuals
with Tourette syndrome, particularly among older subjects. ‘Evening
up’, counting and ritualistic touching are particularly common, though
the checking and contamination concerns of ‘ordinary’ OCD may also
occur.
2 Inattention and hyperactivity symptoms (sometimes amounting to
ADHD) occur in 25–50%, typically emerging before the onset of tics
themselves. It is probably comorbid ADHD rather than the presence of
tics per se that best predicts difficulties with behaviour, peer relation-
ships and learning.
3 Many other less common associations have been described, including
self-injury, failure to inhibit aggression, sleep problems, affective dis-
orders, anxiety disorders, schizotypal personality, intellectual disability,
specific learning difficulties and autistic spectrum disorders.
Differential diagnosis
1 Other dyskinesias may resemble simple tics, but they all differ from tics
in some respects (for example, not increased by relaxation).