A clinically useful definition of stereotypies

An important principle of movement disorders clinical phenomenology is that the clinical setting (the company it keeps) is a critical element for the accurate classification of an abnormal movement. The reason is that the exact same movement is classified differently depending on the clinical setting. For example, repetitive foot tapping might represent a habit in a healthy person, a compulsion when performed in response to an obsession in a patient with obsessive– compulsive disorder, a complex motor tic in a patient with Tourette’s syndrome, or a stereotypy in an autistic individual. Specifying the clinical setting can also help to focus the definition of an entity like stereotypies that has encompassed a heterogeneous set of movements and conditions. I therefore recommend adding the following to the definition of stereotypy proposed by Edwards et al: ‘‘occurring in an individual with impaired mentation or deprived of visual or auditory sensory input. ’’ This change limits the application of the term to the entities most commonly linked to stereotypies and most generally accepted as causes, with impaired mentation including disorders such as autism, mental retardation, dementia, and a variety of encephalopathies. Deprivation of visual or auditory sensory input applies to persons with congenital blindness and deafness. The specification of setting also narrows the entity to conditions that might share a common etiological process that has been hypothesized to cause stereotypies. It has been proposed that social isolation might be a key factor in converting normal developmental stereotypic behavior (eg, thumb sucking) into chronic stereotypies. In this view, autism, mental retardation, dementia, encephalopathies, and congenital deafness and blindness lead to stereotypies because they are each a form of mental or sensory deprivation and isolation. This process has been demonstrated in nonhuman primates and other animals that are isolated during development. An extension of this theory is that when an individual is isolated, stereotypies represent attempts by the person to increase self-stimulation, perhaps to a predetermined level. In support of this possibility, stereotypic behavior is particularly common in animals housed in restrained environments with low stimulation. Alternatively, others have suggested that stereotypies occur as attempts to block out or decrease what is interpreted as an overstimulating environment, being a motor expression of underlying tension and anxiety. Another recommended change to the proposed definition is based on the finding that it is common for stereotypies to include not just ‘‘movement patterns’’ but also vocalizations, such as humming, moaning, or repetitive words or phrases. With these 2 changes, the modified definition for stereotypy would be: a non-goal-directed movement pattern or vocalization that is repeated continuously for a period of time in the same form and on multiple occasions, which is typically distractible, and which occurs in individuals with impaired mentation or deprived of visual or auditory sensory input [changes in italics]. ’’ The use of a more restricted definition should allow identification of a more homogeneous entity and facilitate efforts to better understand and treat the condition.