Stereotypic behaviors are seen in a number of neurologic and psychiatric conditions, as well as in normal people and in animals. They are common in autism; Tourette syndrome; retardation; psychotic disorders, including N-methyl-d-aspartate receptor antibody (NMDAR) encephalitis; neuroleptic-induced tardive syndromes and may be present in some degenerative disorders. Some are medication induced. Head-banging and rocking behaviors are seen in normal children who outgrow them. They are on a continuum with obsessive compulsive spectrum disorders, the umbrella term now used for tics, hair pulling, and a variety of other repetitive, purposeless behaviors. In this article, the authors review these behaviors and put them into the context of the various disorders in which they occur. Stereotypies help define some of the autistic disorders. Treatment is discussed only briefly because evidence to support any intervention is scant.
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• Stereotypies are common behaviors present in humans as well as animals and may or may not reflect pathology.
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• Stereotypies may represent a transient phenomenon in children, but may be associated with a variety of severe neurologic disorders, including specific biochemical disorders such as Rett syndrome and Lesch Nyhan disease, but also in the whole spectrum of autistic disorders and pervasive developmental disorders.
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• Stereotypic disorders may require intervention, especially when harmful, but often do not. Treatment is highly individualized, involving medications or behavioral interventions and often unsuccessful.
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• Stereotypies may occur in neurdegenerative dementing illnesses.
Historical note and terminology
There have been numerous definitions given for the term “stereotypy.” Generally, it has been considered to mean a purposeless, fixed form of expression or response that may interfere with normal behavior. Stereotypies have long been recognized as a possible sign of behavioral pathology. Its occurrence in those with intellectual disability, autism, and schizophrenia has been well established. Perhaps less well appreciated is its occurrence in normal children in the form of head banging, head rolling, and body rocking (95; 76).
Authors writing at the beginning of the 20th century described stereotypy as a central problem in schizophrenia. "The tendency to stereotype produces the inclination to cling to one idea to which the patient then returns again and again," stated Bleuler about schizophrenia (16). This tendency causes, "derailment of . . . associational activity" leading to fixed answers to various questions as well as fixed patterns of motor activities (16). Motor stereotypy is still encountered in schizophrenia, more obviously late in the course (73), but early as well (29), and may occur in catatonia as well (100).
Art depicting the insane and depraved with bizarre facial expressions, abnormal postures, and peculiar gestures consistent with stereotypy predate modern medicine (61).
Caged animals that develop stereotyped pacing have undoubtedly been observed since time immemorial. Pacing occurs in imprisoned humans as well. Experiments on primates in the 1950s revealed that certain stereotyped behaviors, due to social and sensory deprivation in particular, led to permanent stereotypies that could not be altered if the deficit occurred during critical periods in brain development (89). Stereotypies in commercially raised animals have raised concerns about the increasingly efficient but less humane conditions of modern animal husbandry (31). However, laboratory scientists have pointed out that pacing behavior may be pathologic in some species but not others (86). In certain strains of horses, stereotyped behaviors are common (75). Human studies in autistic children reported that stereotypy interfered with learning (56) and implied that controlling stereotypic behavior was a necessary precondition for learning. Thus, understanding stereotypy became more important for developing rational therapies.
It must be noted that stereotypies may also occur during development of congenitally blind (111) or deaf children (07; 101; 17; 96) who are otherwise normal. Certain movements that give an appearance of restlessness may be part of an individual’s repertoire of movements, also referred to as mannerisms or habits, and are seen in otherwise normal individuals. One of the more common stereotypies manifests as restless movements in the legs, described as “leg stereotypy disorder” (52) or leg stereotypy syndrome (63), which is defined as a repetitive, continuous movement present almost exclusively in the legs while the patient is seated. In contrast to restless legs syndrome, which usually occurs at night, there is no diurnal variation in leg stereotypy disorder, and many individuals affected by this condition may not be aware that they have the repetitive movement until it is pointed out to them. Frequently familial, the epidemiology, pathophysiology, or treatment of leg stereotypy disorder have not been studied. Comparing 92 subjects with restless legs syndrome, Parkinson disease, Tourette syndrome, and tardive dyskinesia with their companions of similar age, Lotia and colleagues reported leg stereotypy syndrome in 7% of individuals in the control group and 17% in the movement disorder group (63). The movements involved predominantly one leg, and all had a family history of a similar disorder.
The concept of a "tardive stereotypy" (104; 51; 70; 83) was introduced to describe a neuroleptic drug-induced condition that had previously been classified as a complex set of superimposed tardive movement disorders centering about dystonia but also including dyskinesias (choreoathetosis) and pseudoakathisia. There are differences of opinion about the nomenclature of the phenomenological distinctions between tardive stereotypies and tardive dyskinesias, as the latter usually do not clearly fit the definition of a choreoathetoid movement.
Until the 1990s, the concept of stereotypic behaviors, both as a part of a pathologic mental syndrome and as a movement disorder, fell outside the usual purview of neurology and within the disciplines of psychiatry, developmental medicine, and psychology. As the border between neurology and psychiatry continues to blur, stereotypy has become a subject of concern for neurologists, psychiatrists, and pediatricians (62; 50; 08). With the recognition of dopamine agonist-induced compulsive behaviors in Parkinson disease, such as gambling, hypersexuality, “punding,” and, to a lesser extent, in restless legs syndrome, the underlying mechanisms of “forced” behaviors have attracted increasing scientific attention.