|The predominant manifestation in
these syndromes is some form of tic. A tic is an
involuntary, rapid, recurrent, non-rhythmic motor
movement (usually involving circumscribed muscle groups),
or vocal production, that is of sudden onset and serves
no apparent purpose. Tics tend to be experienced as
irresistible but they can usually be suppressed for
varying periods of time. Both motor and vocal tics may be
classified as either simple or complex, although the
boundaries are not well defined. Common simple motor tics
include eye-blinking, neck-jerking, shoulder-shrugging,
and facial grimacing. Common simple vocal tics include
throat-clearing, barking, sniffing, and hissing. Common
complex tics include hitting one's self, jumping, and
hopping. Common complex vocal tics include the repetition
of particular words, and sometimes the use of socially
unacceptable (often obscene) words (coprolalia), and the
repetition of one's own sounds or words (palilalia).
There is immense variation in the severity of tics. At the one extreme the phenomenon is near-normal, with perhaps 1 in 5 to 1 in 10 children showing transient tics at some time. At the other extreme, Tourette's syndrome is an uncommon, chronic, incapacitating disorder. There is uncertainty about whether these extremes represent different conditions or are opposite ends of the same continuum; many authorities regard the latter as more likely. Tic disorders are substantially more frequent in boys than in girls and a family history of tics is common.
The major features distinguishing tics from other motor disorders are the sudden, rapid, transient, and circumscribed nature of the movements, together with the lack of evidence of underlying neurological disorder; their repetitiveness; (usually) their disappearance during sleep; and the ease with which they may be voluntarily reproduced or suppressed. The lack of rhythmicity differentiates tics from the stereotyped repetitive movements seen in some cases of autism or of mental retardation. Manneristic motor activities seen in the same disorders tend to comprise more complex and variable movements than those usually seen with tics. Obsessive compulsive activities sometimes resemble complex tics but differ in that their form tends to be defined by their purpose (such as touching some object or turning a number of times) rather than by the muscle groups involved; however, the differentiation is sometimes difficult.
Tics often occur as an isolated phenomenon but not infrequently they are associated with a wide variety of emotional disturbances, especially, perhaps, obsessional and hypochondriacal phenomena. However, specific developmental delays are also associated with tics.
There is no clear dividing line between tic disorder with some associated emotional disturbance and an emotional disorder with some associated tics. However, the diagnosis should represent the major type of abnormality.