82 Neurodevelopmental Disorders
other specified and unspecified tic disorders), such that once a tic disorder at one level of the
hierarchy is diagnosed, a lower hierarchy diagnosis cannot be made (Criterion E).
Tics are sudden, rapid, recurrent, nonrhythmic motor movements or vocalizations. An
individual may have various tic symptoms over  time, but at any point in time, the tic rep-
ertoire recurs in a characteristic fashion. Although tics can include almost any muscle group
or vocalization, certain tic symptoms, such as  eye blinking or throat clearing, are common
across patient populations. Tics are generall y experienced as involun tary but can be vol-
untarily suppressed for varying lengths of time.
Tics can be either simple or complex. Simple motor tics  are of short duration (i.e., milli-
seconds) and can include eye blinking, should er shrugging, and extension of the extrem-
ities. Simple vocal tics include throat clea ring, sniffing, and grunting often caused by
contraction of the diaphragm or  muscles of the oropharynx. Complex motor tics  are of lon-
ger duration (i.e., seconds) and often include a combination of simple tics such as simul-
taneous head turning and shoulder shrugging . Complex tics can appear purposeful, such
as a tic-like sexual or obscene gesture ( copropraxia ) or a tic-like imitation of someone else’s
movements ( echopraxia). Similarly, complex vocal tics include repeating one’s own sounds
or words ( palilalia ), repeating the last-heard word or phrase ( echolalia ), or uttering socially
unacceptable words, including obscenities,  or ethnic, racial, or religious slurs ( coprolalia ).