Definitions and Classification of TIC Disorders
The Tourette Syndrome Classification Study Group
Tics are brief movements (motor tics) or sounds (vocal tics) that occur intermittently and unpredictably out of a background of normal motor activity. Although tics can appear as the result of direct brain injury (so-called symptomatic, e.g., from head trauma or encephalitis), they most commonly are idiopathic and are part of the spectrum of Gilles de la Tourette syndrome or other idiopathic tic disorders. To aid investigators searching for the gene(s) causing Tourette syndrome, criteria are proposed to classify the idiopathic tic disorders. Although some of these separate entities may ultimately be shown to be caused by the same gene, until that is established, it is considered best when searching for the Tourette's gene to have tic disorders classified into distinct, homogeneous entities. The proposed classification will likely change over time as better diagnostic techniques become available and can both expand and consolidate, particularly after the Tourette gene is located.
(Arch Neurol. 1993;50:1013-1016)
Because studies searching for the gene(s) associated with Tourette syndrome are under way at several centers around the world, the Tourette Syndrome Association (TSA), New York, NY, recognized the need for developing precise criteria to define the syndrome and related tic disorders. These criteria could be utilized not only in genetic research but also in other research activities as well as by clinicians in practice. Consistency in diagnosis is important so that investigators will be able to compare the same populations of patients, and all who read the scientific reports from the various research groups will be better able to interpret the results. The TSA, furthermore, recognized the need for clinical investigators to have available clinical rating scales to follow the natural history of the disease and to evaluate results of therapeutic interventions.
To these ends, the TSA organized a task force (The Tourette Syndrome Classification Study Group) to develop definitions and rating scales. The workshop participants were able to prepare and agree on research definitions of various tic disorders and have set up a subcommittee to develop clinical rating scales. The definitions were further discussed and modified several times until agreement was reached on this final report, which we now present to the biomedical community (Table 1). A subcommittee is developing a quantitative rating scale for tics, and we anticipate having available in the near future a rating scale that will prove valid, reliable, and easy to use. When such a scale is finalized, it will also be published.
Although definitions of Tourette syndrome are available in textbooks of neurology and psychiatry and also in the Diagnostic and Statistical Manual, Revised Third Edition (DSM-IIIR) of the American Psychiatric Association (1988), they do not effectively differentiate among nor define the wide variety of all the tic disorders. Discussions centered on possible approaches to developing more effective acceptable definitions. The Study Group decided to keep the basic tenets of the DSM-IIIR definition for Tourette syndrome, chronic tic disorder, transient tic disorder, and non-specified tic disorder, since these terms have become widely used, and there is no solid reason to abandon them. However, for research purposes we divided each of these DSM-IIIR definitions into two categories: "definite," in which the tics have been witnessed by a reliable observer, and "historical," in which the putative tics have not been reliably witnessed. These definitions are reported here in greater detail, along with the definitions of other categories of tic syndromes that were developed at the workshop and are not covered by existing DSM-IIIR criteria. These additional tic categories are chronic single tic disorder; definite tic disorder-diagnosis deferred; and probable Tourette syndrome.
The diagnostic categories depend on the presence of tics alone, although patients with Tourette syndrome may have behavioral problems or mental disorders that may overshadow the tic disorder in severity, impairment, or impact on normal functioning1. These behavioral problems may precede the onset of tics or may follow the onset of tics by months or years. An individual who is suffering from more than one condition (i.e., tics and a psychiatric disorder) is probably more likely to be seen by a clinician than is an individual who suffers from tics alone. Compared with the general population, individuals with Tourette Syndrome who are seen for clinical care appear to have a higher frequency of many different behavioral symptoms, including obsessions, compulsions, hyperactivity, inattention, learning disabilities, impulsivity, immaturity, emotional lability, anxiety, and depression. Investigators have differed in their interpretation as to how these symptoms relate to Tourette syndrome. Some investigators have considered these problems as associated or secondary responses to the tics or as coincidental conditions2, while others have felt that some specific mental disorders (particularly obsessive-compulsive disorder) are intrinsically related to the Tourette syndrome spectrum.3 One view point includes all of these and other symptoms and diagnoses as expanded manifestations of Tourette syndrome.4 We need more carefully designed studies to resolve the controversy about the exact type, extent, and causative relationship of these behavioral symptoms and Tourette syndrome.
Since the criteria and definitions for tic disorders depend on the clinical phenomenology and natural history of the tics that are present in an individual person, it is essential first to describe inclusive and exclusive features for both motor and vocal tics.
Tics are brief movements (motor tics) or sounds produced by moving air through the nose, mouth, or throat (vocal tics). In contrast with many other movement disorders, they are not constantly present (except when extremely severe) and occur out of a background of normal motor activity.5
Motor tics can be simple or complex in appearance. Simple motor tics are abrupt, sudden, and brief movements, occurring in single and isolated fashion. Examples of simple motor tics include an eye blink, a shoulder shrug, head jerk, dart of the eyes, or twitch of the nose. If only one type of simple jerk is present and it always remains the same, it might be considered either a mannerism or a nonvarying tic. Simple motor tics may be difficult to distinguish from myoclonic or choreic jerks. However, even when tics are simple jerks, more complex forms of tics may also be present, allowing one to establish the diagnosis by "the company it keeps." Moreover, simple motor tics are often repetitive, such as a run of eye blinks, a series of arm jerks, or a run of facial twitches. These qualities distinguish tics from myoclonus and chorea.
Repetitive eye blinking, however, is also seen in mild idiopathic blepharospasm, which is considered a form of focal dystonia.6 Fortunately, the blinking from tics and from blepharospasm can usually be differentiated from each other either by the presence of other tics or by the presence of dystonic movements at other sites. Also, tics almost always begin in childhood, while blepharospasm is predominantly a disorder of the older adult population.
In contrast with the more common rapid myocloniclike jerks, tics can also present as sustained contractions, resembling dystonic movements, which are, therefore, termed tonic or dystonic tics. A major differential feature is that torsion dystonia is a continual hyperkinesia, usually twisting in pattern, that can result in a sustained abnormal posture. Dystonic tics are abrupt bursts of movement that are sustained in a posture, usually for a short duration. They do not tend to be continuous. The presence of the more typical clonic tics in other body regions should raise the likelihood that the sustained contractions could be dystonic tics rather than torsion dystonia. A run of simple motor tics could be considered at the borderline between simple and complex motor acts. Complex tics are distinct, coordinated patterns of sequential movements. They may appear purposeful, as if performing a voluntary motor act. Examples of complex tics that appear purposeful include such acts as touching the nose, touching other people, smelling objects, jumping, copropraxia (obscene gestures), and echopraxia (mimicking movements performed by others). Examples of complex tics that appear nonpurposeful include head shaking associated with shoulder shrugging, repetitive kicking of legs, and a sequential display of a variety of facial movements.
Other movement disorders that present with complex movements but are commonly considered distinct from tics, are (1) the repetitive complex movements, known as stereotypies, of patients with hyperactivity, mental retardation, or psychosis; (2) hyperekplexia, which is an excessive startle syndrome; (3) akathitic movements (initiated to overcome a feeling of inner restlessness); (4) the rituals of the obsessive-compulsive; (5) the "hand caressing" movements in Rett's syndrome (a syndrome in young girls with autism, dementia, and motor difficulties); and (6) a variety of movements that occur in the restless legs syndrome. All these other complex movements can sometimes be difficult to distinguish from complex motor tics, and the correct diagnosis of tics is usually made by exclusion of these other diagnoses or by finding an association with simple motor tics or vocal tics.
Motor tics usually recur in the same part of the body, and multiple regions of the body can be involved. The expressions of the tics are not necessarily identical from occurrence to occurrence, even within the same body part. Moreover, over time, tics often recede from one part of the body and evolve elsewhere.
Tics occur as an involuntary movement or as a response to an urge to perform the movement, which transiently relieves the sensation. The label of "unvoluntary" movement is used to fit this latter situation, ie, the movement is a response to relieve an unpleasant sensation. These "unvoluntary" movements are commonly perceived by the patient as voluntary7 and, therefore, are often, but not always, partially or fully temporarily suppressible. Unless the disorder is very severe, most individuals with tics can voluntarily suppress them for various periods of time.8 This is in contrast with other hyperkinetic movement disorders, which can be suppressed for only very short durations, if at all.8 But when tics are suppressed, an inner tension of discomfort tends to build up, which is relieved only by an increased burst of tics.
Even without suppression of the tics, motor tics are often preceded by a generalized or focal uncomfortable feeling that usually is relieved by the movement. These sensory phenomena have some resemblance to those associated with akathisia and the restless legs syndrome. In these two disorders, motor movement also relieves the unpleasant sensation, and both akathitic movements and the walking about by individuals with the restless legs syndrome can be considered the direct result of the voluntary motor behavior to bring about such relief, ie, "unvoluntary," as mentioned above. Individuals with tics may have either a generalized or a localized sensation of tension that is relieved by movement, ie, the tic. The focal, localized uncomfortable sensations relieved by movement of the affected body region has been called sensory tics, and these are seen in approximately 40% of patients with Tourette syndrome.9 Sensory tics are recurrent dysphoric somatic sensations of pressure, tickle, warmth, cold, pain, or other sensations in localized regions that are temporarily relieved by a movement.10 How different and specific these focal sensations are compared with the generalized discomfort often preceding a tic is not certain. One view is that the motor or vocal action in response to a sensory tic is voluntary, whereas the motor or vocal action relieving the generalized discomfort is involuntary, 9,10 and, hence, a motor or vocal tic.
Involuntary ocular movements can be an important feature for differentiation of tics from other dyskinesias. Whether a brief jerk of the eyes or a more sustained eye deviation, ocular movements can occur as a manifestation of motor tics.11 Recognizing this is important because very few other dyskinesias involve ocular movements. The exceptions are (1) opsoclonus (dancing eyes), which is a form of myoclonus, (2) ocular myoclonus (rhythmic vertical oscillations at a rate of 2 Hz) that often accompanies palatal myoclonus, and (3) oculogyric spasms (a sustained deviation of the eyes) most often associated with neuroleptics or as a consequence of encephalitis lethargica.
Other paroxysmal dyskinesias usually present no difficulty in diagnosis. Paroxysmal kinesigenic choreoathetosis (or dystonia) is triggered by sudden movement, lasts seconds, and is suppressed with anticonvulsant therapy. Paroxysmal nonkinesigenic dystonia lasts minutes to hours, too long to be confused with the brief bursts of tics.
Vocal tics represent involuntary sounds produced by moving air through the nose, mouth, or throat. They can also be referred to as phonic tics. Some members of the Tourette Syndrome Classification Study Group preferred the term vocal/phonic tics. The Study Group resolved the controversy by deciding that all three terms are synonymous and equivalent. For simplicity, we have called them vocal tics in this article.
These sounds range from simple throat-clearing sounds and sniffing to grunts to verbalizations of syllables and words. Vocal tics can also be utterances of inappropriate, undesired statements or obscenities (coprolalia). Like somatic motor tics, vocal tics can also be divided into simple and complex tics. Single sounds, such as throat clearing, barking, and sniffing, represent simple vocal tics. Verbalizations (the expression of words), including coprolalia, echolalia (repeating of the words of others), and palilalia (repeating of the individual's own words) can be considered complex vocal tics.
Involuntary and "unvoluntary" phonations occur in only a few other neurologic disorders. These include the moaning in akathisia, in severe parkinsonism, in progressive supranuclear palsy, and from levodopa toxicity; the brief sounds in oromandibular dystonia, Huntington's disease, neuroacanthocytosis, and tardive dyskinesia; and the sniffing and spitting occasionally encountered in Huntington's disease and neuroacanthocytosis. The humming and coughing encountered in some patients with blepharospasm or Meige syndrome should be considered voluntary since they are used as tricks to suppress the dystonic movements.
Like motor tics, vocal tics frequently change and vary in severity over time, and both remissions and exacerbations are common.
Accepted for publication March 22, 1993.
The following persons, listed with their affiliated institutions, participated in the formulation of these definitions and the classification of tic disorders: Stanley Fahn, MD (Chairman) Columbia-Presbyterian Medical Center, New York, NY; Ruth D. Bruun, MD, Chairman, Tourette Syndrome Association Medical Committee, New York, NY; Eric Caine, MD, University of Rochester (NY); Donald J. Cohen, MD, Yale University, New Haven, Conn; David E. Comings, MD, City of Hope Medical Center, Duarte, Calif; Peter G. Como, PhD, University of Rochester (NY); P. Michael Conneally, PhD, University of Indiana, Indianapolis; Stephen T. Gancher, MD, University of Oregon, Portland; Christopher Goetz, MD, Rush-Presbyterian-St Luke's Medical Center, Chicago, Ill; Gerald S. Golden, MD, University of Tennessee, Memphis; Joseph Jankovic, MD, Baylor College of Medicine, Houston, Tex; Roger Kurlan, MD , University of Rochester (NY); Peter LeWitt, MD, Sinai Hospital-Wayne State University, Detroit, Mich; David Pauls, PhD, Yale University, New Haven, Conn; Mark A. Riddle, MD, Yale University, New Haven, Conn; Arthur K. Shapiro, MD, Mount Sinai School of Medicine, New York (NY); and Harvey S. Singer, MD, The Johns Hopkins University, Baltimore, Md.
Reprint requests to Neurological Institute, 710 W 168th St, New York, NY 10032 (Dr Fahn).
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