Criterion B states that the stereotypic movements interfere with social, academic, or other activities and, in some children, may result in self—injury (or would if protective mea- sures were not used). If self—injury is present, it should be coded using the specifier. Onset of stereotypic movements is in the early developmental period (Criterion C). Criterion D states that the repetitive, stereotyped behavior in stereotypic movement disorder is not at- tributable to the‘physiological effects of a substance or neurological condition and is not better explained by another neurodevelopmental or mental disorder. The presence of stereotypic movements may indicate an undetected neurodevelopmental problem, espe- cially in children ages 1—3 years.
Simple stereotypic movements (e.g., rocking) are common in young typically developing chil- dren. Complex stereotypic movements are much less common (occurring in approximately 3%—4%). Between 4% and 16% of individuals with intellectual disability (intellectual develop- mental disorder) engage in stereotypy and self-injury. The risk is greater in individuals with severe intellectual disability. Among individuals with intellectual disability living in res- idential facilities, 10%—15% may have stereotypic movement disorder with self—injury.
Stereotypic movements typically begin within the first 3 years of life. Simple stereotypic move- ments are common in infancy and may be involved in acquisition of motor mastery. In chil- dren who develop complex motor stereotypies, approximately 80% exhibit symptoms before 24 months of age, 12% between 24 and 35 months, and 8% at 36 months or older. In most typ- ically developing children, these movements resolve over time or can be suppressed. Onset of complex motor stereotypies may be in infancy or later in the developmental period. Among individuals with intellectual disability, the stereotyped, self—injurious behaviors may persist for years, even though the typography or pattern of self-injury may change.
Environmental. Social isolation is a risk factor for self—stimulation that may progress to stereotypic movements with repetitive self—injury. Environmental stress may also trigger stereotypic behavior. Fear may alter physiological state, resulting in increased frequency of stereotypic behaviors.
Genetic and physiological. Lower cognitive functioning is linked to greater risk for stereo- typic behaviors and poorer response to interventions. Stereotypic movements are more fre- quent among individuals with moderate-to-severe/profound intellectual disability, who by
Virtue of a particular syndrome (e.g., Rett syndrome) or environmental factor (e.g., an environ- ment with relatively insufficient stimulation) seem to be at higher risk for stereotypies. Repet- itive self-injurious behavior may be a behavioral phenotype in neurogenetic syndromes. For example, in Lesch-Nyhan syndrome, there are both stereotypic dystonic movements and self- mutilation of fingers, lip biting, and other forms of self—injury unless the individual is re- strained, and in Rett syndrome and Cornelia de Lange syndrome, self-injury may result from the hand-to—mouth stereotypies. Stereotypic behaviors may result from a painful medical con- dition (e.g., middle ear infection, dental problems, gastroesophageal reﬂux).
Stereotypic movement disorder, with or without self—injury, occurs in all races and culhares.
Cultural attitudes toward unusual behaviors may result in delayed diagnosis. Overall cultural tolerance and attitudes toward stereotypic movement vary and must be considered.