| Tic | |
|---|---|
| Classification and external resources | |
| MeSH | D020323 |
A tic is a sudden, repetitive, nonrhythmic, stereotyped motor movement or vocalization involving discrete muscle groups.[1][2] Tics can be invisible to the observer, such as abdominal tensing or toe crunching. Common motor and phonic tics are, respectively, eye blinking and throat clearing.[3] Movements of other movement disorders (for example, chorea, dystonia, myoclonus) must be distinguished from tics. Other conditions, such as autism and stereotypic movement disorder, also include movements which may be confused with tics. Tics must also be distinguished from the compulsions of OCD and from seizure activity.
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| Video clips of tics |
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| HBO documentary video clip |
| CBS News video clip |
| From the TSA, an adult with tics |
Tics are classified as motor vs. phonic and simple vs. complex.
Motor tics are movement-based tics affecting discrete muscle groups.
Phonic tics are involuntary sounds produced by moving air through the nose, mouth, or throat. They may be alternately referred to as verbal tics or vocal tics, but most diagnosticians prefer the term phonic tics to reflect the notion that the vocal cords are not involved in all tics that produce sound.[4]
Tics may increase as a result of stress, fatigue, boredom, or high-energy emotions, which can include negative emotions, such as anxiety, but positive emotions as well, such as excitement or anticipation. Relaxation may result in a tic increase (for instance, watching television or using a computer), while concentration on an absorbing activity often leads to a decrease in tics.[5][6] Neurologist and writer Oliver Sacks described a physician with severe Tourette syndrome (Canadian Mort Doran, M.D., a pilot and surgeon in real life, although a pseudonym was used in the book), whose tics remitted almost completely while he was performing surgery.[7][8]
Immediately preceding tic onset, most individuals are aware of an urge[9] that is similar to the need to yawn, sneeze, blink, or scratch an itch. Individuals describe the need to tic as a buildup of tension[10] that they consciously choose to release, as if they "had to do it".[11] Examples of this premonitory urge are the feeling of having something in one's throat or a localized discomfort in the shoulders, leading to the need to clear one's throat or shrug the shoulders. The actual tic may be felt as relieving this tension or sensation, similar to scratching an itch. Another example is blinking to relieve an uncomfortable sensation in the eye.
Tics are described as semi-voluntary or unvoluntary,[12] because they are not strictly involuntary—they may be experienced as a voluntary response to the unwanted, premonitory urge. A unique aspect of tics, relative to other movement disorders, is that they are suppressible yet irresistible;[13] they are experienced as an irresistible urge that must eventually be expressed.[12] Some people with tics may not be aware of the premonitory urge. Children may be less aware of the premonitory urge associated with tics than are adults, but their awareness tends to increase with maturity.[12]
Simple motor tics are typically sudden, brief, meaningless movements that usually involve only one group of muscles, such as eye blinking, head jerking or shoulder shrugging.[14] Motor tics can be of an endless variety and may include such movements as hand clapping, neck stretching, mouth movements, head, arm or leg jerks, and facial grimacing.
A simple phonic tic can be almost any sound or noise, with common vocal tics being throat clearing, sniffing, or grunting.[14]
Complex motor tics are typically more purposeful-appearing and of a longer nature. They may involve a cluster of movements and appear coordinated.[14] Examples of complex motor tics are pulling at clothes, touching people, touching objects, echopraxia and copropraxia.
Complex phonic tics may fall into various series (categories), including echolalia (repeating words just spoken by someone else), palilalia (repeating one's own previously spoken words), lexilalia (repeating words after reading them) and coprolalia (the spontaneous utterance of socially objectionable or taboo words or phrases). Coprolalia is a highly publicized symptom of Tourette syndrome; however, only about 10% of TS patients exhibit coprolalia.[14]
Complex tics are rarely seen in the absence of simple tics. Tics "may be challenging to differentiate from compulsions",[15] as in the case of klazomania (compulsive shouting).
Tic disorders occur along a spectrum, ranging from mild to more severe, and are classified according to duration and severity (transient tics, chronic tics, or Tourette syndrome). Tourette syndrome is the more severe expression of a spectrum of tic disorders, which are thought to be due to the same genetic vulnerability. Nevertheless, most cases of Tourette syndrome are not severe.[16] The treatment for the spectrum of tic disorders is similar to the treatment of Tourette syndrome.
Dystonias, choreas, other genetic conditions, and secondary causes of tics should be ruled out in the differential diagnosis.[17] Conditions besides Tourette syndrome that may manifest tics or stereotyped movements include developmental disorders, autism spectrum disorders,[18] and stereotypic movement disorder;[19][20] 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's syndrome, XYY syndrome and fragile X syndrome. Acquired causes of tics include drug-induced tics, head trauma, encephalitis, stroke, and carbon monoxide poisoning.[17][21] 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.[16]
Although tic disorders are commonly considered to be childhood syndromes, tics occasionally develop during adulthood; adult-onset tics often have a secondary cause.[22] Tics that begin after the age of 18 are generally not considered symptoms of Tourette's syndrome.
Tests may be ordered as necessary to rule out other conditions: for example, when diagnostic confusion between tics and seizure activity exists, an EEG may be ordered, or symptoms may indicate that an MRI is needed to rule out brain abnormalities.[23] TSH levels can be measured to rule out hypothyroidism, which can be a cause of tics. Brain imaging studies are not usually warranted.[23] 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.[17] most cases are mild.[24]
Tics must be distinguished from fasciculations. Small twitches of the upper or lower eyelid, for example, are not tics, because they do not involve a whole muscle. They are twitches of a few muscle fibre bundles, which one can feel but barely see.[25]
There is some confusion in media portrayals of tics; by sensationalizing the symptoms of Tourette's, the video media have contributed to warped perceptions about tics.
The Tourette Syndrome Classification Study Group. "Definitions and classification of tic disorders". Arch. Neurol. 50 (10): 1013-6. PMID 8215958. Retrieved on 2005-03-22
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