Jarrett Barnhill M.D.
University of North Carolina School of Medicine
Stereotypic Movement Disorder (SMD) encompasses both repetitive and self-injurious behaviors (SIB). This combination results in a clinically diverse syndrome that differs across a spectrum of typologies, topographies, severity, affective states, pain responses, hypothesized motivation, and neuropsychiatric comorbidity (baseline exaggeration). Other sources of variability include environmental or ecological conditions, medical complications, or expressions of specific behavioral phenotypes associated with several genetic disorders (Schroeder et al., 2001; Barnhill, 2003). In order to make sense of this diversity, the clinician needs to look beyond current descriptive criteria and categorical approaches to diagnosis that incorporates the underlying biopsychosociology of SMD. This paper focuses more specifically on neurobiology but in no way minimizes the critical role of environmental and interpersonal factors in SMD.
Stereotypic behaviors include a broad spectrum of repetitive behaviors that vary in topography, typology, intensity, and degree of interference with daily activities or task demands. Although stereotypies are well studied from a behavioral perspective, it may still be helpful to address and define the differences between subtypes of SMD across the range of intellectual disabilities (Castellanos, Ritchie, Marsh, & Rapoport, 1996). For example, clinicians may wish to sub-classify SMD based on hypothesized differences in motivational states. Some repetitive behaviors are involuntary and neurologically based (seizure activity or sleep related movements). Others appear related to levels of alertness and arousal (Troster, 1994) and are neither associated with specific stressors, nor appear intrinsically reinforcing. A third subset of stereotypic behaviors emerges in boring or under-stimulating environments (termed vacuous behaviors by ethologists) and occurs with little evidence of intrinsic reinforcement or relief from distress (Barnhill, 2003; Hall, Thorns, & Oliver, 2003).
A fourth subtype of stereotypic behavior emerges during periods of distress or increased environmental demands. These stereotypic movements appear to reduce dysphoric over-arousal, and thereby allow the individual to "escape" from the precipitating circumstances. This group of stereotypies results in a pattern of negative reinforcement (Bodfish & Madison, 1993; Castellanos et al., 1996). Clinically, individuals with severe developmental disabilities, comorbid neurological disorders, and difficult temperament are more likely to display this pattern of stereotypic behaviors (Schroeder et al., 2001).
In some vulnerable children these "escape" stereotypies will undergo a developmental transformation towards SIB (Schroeder et al., 2001; Hall et al., 2003). The factors related to this transformation, such as level of intellectual disability, genetic risks, neurodevelopmental disorders, or temperamental style deserve careful attention. A similar metamorphosis may occur with the onset of a new psychiatric or mental disorder. (Buitelaar 1993; Schroeder et al., 2001).
Self-injurious behaviors (SIB) also differ across multiple domains (Schroeder et al., 2001). In order to accommodate this diversity, it is clear that clinicians need to sub-categorize SIB based on differences in typology, topography, intensity, associated pain threshold, trigger events, and reinforcement strategies (Schroeder et al., 2001; Sandman, Touchette, Lenjavi, & Chizc-Demet, 2003). For example, tissue damage is a reliable marker for the severity of SIB. Tissue damage can result from high frequency/low severity behaviors such as compulsive cuticle picking or nail biting, or as the result of infrequent but severe forms of self-mutilation. These different subtypes of SIB point to the need for a multi-factorial rather than a single factor (presenting target behaviors) approach to self-injury.
The prevalence rate for SIB varies inversely with the level of intellectual disability. Other vulnerability factors for SIB include the presence of comorbid pervasive developmental disorders (autism), CNS damage, and irritable/affectively labile, intensely reactive temperament (Barnhill 2003). SIB may also occur in primary psychiatric disorders. Interestingly, individuals with specific psychiatric disorders may differ in terms of frequency, severity, and typology of SIB. For example the apparent motivation and typology of SIB may differ between people with borderline personality disorder (BPD) and those with schizophrenia, mood disorders, or posttraumatic stress disorder. This observation suggests that there may be not only syndrome-related, typological differences, but also significant diversity in trigger stimuli, pain threshold, and the longitudinal course of symptoms--state versus trait-related differences (Castellanos et al., 1996; Mendez & Mirea, 1998; Saxena, Bota, & Brody, 2001; Barnhill, 2003).
Developmental aspects of SMD
SMD (including SIB) appears to follow a developmental course (Troster, 1994). For some affected individuals, severe behaviors appear during childhood but abate with aging. For others, SMD follows a different developmental course, progressing from low intensity stereotypic behaviors (rocking or nail biting) towards severe self-injurious behaviors. The severity of ID, presence of autism, and other neurodevelopment disorders influence the direction of this transformation (Schroeder et al., 2001; Barnhill, 2003).
In addition to evolving changes in typology and severity, some individuals appear to undergo a transformation in hypothesized motivation for SMD. Young children may present with SMD that appears initially as intrinsically motivated but over time gradually evolves towards behaviors that result in transient escape from task demands or unsettling environments. Over time, these escape behaviors intensify and transform from stereotypic or compulsive behaviors in the direction of SIB (Barnhill, 2003; Hall et al., 2003).
The diagnosis of SMD involves both inclusion (symptoms) and exclusion criteria. Exclusion criteria are used to segregate SMD from tic, obsessive-compulsive, and pervasive developmental disorders. But there are problems inherent in this method. For example, there is a wide range of repetitive behaviors observed in individuals with tic disorders (Bruun & Budman, 1998; Iiada et al., 1996). Simple tics are readily differentiated but the situation becomes more complex in the face of complex tics, tics associated with sensory phenomenon (Bodfish & Madison, 1993; Scahill, Leckman, & Marck, 1995) and self-injury (Bruun & Budman, 1993; Robertson, 1992; Poustka & Lisch, 1993). In addition, tics may intensify during periods of increased stress or excessive task demands. This sensitivity to environmental stresses can mislead the clinician into believing that the observed worsening of symptoms is a voluntary phenomenon, or is an intentional effort to escape demand situations.
Tic-related behaviors such as skin picking or nail biting may be diagnosed as SMD-these tend to occur in low demand settings. Individuals with severe Tourette Disorder may have bouts of severe self-injury that is triggered by sensory phenomena and terminated only when "it feels right." For example, pain may serve to focus hitting to a specific topography, or terminate when the individual's pain threshold is reached (Robertson, 1992; Robertson, 2000; Rapin, 2001).
Differentiating SMD from obsessive-compulsive disorder can be a complicated process. Although some SMD (self-injury) may present with significant subjective distress, insight, attempts at suppression, or obsessions; most seem to either involve behavioral typologies that differ from classic OCD symptoms (checking, contamination, doubting, or obsessive forms of the disorder), or lack the characteristic relationship to anxiety-producing obsessions (Poustka & Lisch 1993). These SMD resemble repetitive behaviors associated with OC spectrum or tic disorders-lacking antecedent obsessive thoughts, subjective distress, anxiety, behavioral inhibition, harm avoidance, and appear impulsive or self-reinforcing features (Bruun & Budman; 1993; Iiada et al., 1996; Hollander & Rosen, 1999).
Among individuals with PDDs, it may become exceedingly difficult to clinically prioritize syndrome related stereotypic or self-injurious behavior from other repetitive behaviors associated with SMD (Poustka & Lisch, 1993). For example, the prevalence of SMD-like behaviors in people with autistic spectrum disorders may correlate more with the level of intellectual disability or psychiatric comorbidity rather than PDD per se (Buitelaar, 1993; Leary & Dill, 1998; Rapin, 2001). A dissonance arises when severe SIB occurs in children with high functioning autism or Asperger syndrome. Self-injury in this high functioning group tends to be less common, so when present suggests exceptional circumstances-e.g. onset of comorbid psychiatric illness. Unfortunately, the current DSM-IV-TR criteria for SMD exclude individuals with PDD. This exclusion creates an ambiguity, a misconception that SIB is a basic feature of autistic spectrum disorders.
Medical, neurological, and genetic factors play a key role in SMD. For example, comorbid medical conditions (headaches or constipation), behavioral phenotypes (Lesch-Nyhan, Prader Willi, Fragile X or Smith Magennis syndrome) (Schroeder et al., 2001), or drug side effects (akathisia) (Blaisdell, 1994) affect the typology and prevalence rates of SIB. SIB is also reported in selected neurodegenerative disorders such as neuroacanthocytosis (Saint-Cyr, Taylor et al 1995). For medical conditions, it is helpful to establish a link between the onset or changes in SMD and the condition is question (Leary, Hill 1996; Saint-Cyr, Taylor, & Nicholson, 1995).
Cyclical changes or clustering of SMD/SIB can be misattributed to mood disorder, especially bipolar disorder. On closer analysis, underlying medical problems may show a waxing and waning course-constipation, seasonal allergies-to fluctuate over time. Although similar in many respects, changes in SMD (baseline exaggeration) due to a primary psychiatric disorder may differ from those associated with medical conditions in terms of duration and direct linage to medical issues. (Bodfish & Madison, 1993; Schroeder et al., 2001; Hall et al., 2003). For example, clinicians have noted for some time the role of pain in initiating or maintaining stereotypies and SIB. These clinical insights are now being supported by emerging research into the basic neurobiology of pain and nociception (Sandman et al., 2003). Variations in pain thresholds, emotional responses (nociception), and endorphins release and sensitivity suggest that pain responses may play a complex, and as yet poorly understood role in SIB (Schroeder et al., 2001; Sandman et al., 2003).
Treatment should be individualized and focused on this working hypothesis that includes etiological or trigger events, factors that maintain the SMD, and the presence of diagnosable primary psychiatric, genetic (behavioral phenotypes), neurological, and medical conditions. Assessment involves a careful behavioral analysis and active investigation for primary neuropsychiatric conditions. A combination of these data collection systems provides data on both learning and underlying physiological variables. Multi-factorial measurements of treatment response are also crucial.
Recent studies point to the role of neurotransmitters in repetitive-stereotypic behaviors, and self-injury. Abnormalities in pathways that utilize serotonin (Bodfish & Madison, 1993), dopamine (Sivam, 1996), endorphins, and other neuropeptides (Campbell, Anderson, Small, Adams, Gonzalez, & Ernst, 1993; Sandman et al., 2003) are under continuing investigation. For example dopamine excess in the context of decreased serotonin activity may play a role in a range of repetitive behaviors and self-injury. But the diversity of SMD and SIB make any single neurotransmitter model suspect.
A reality check of our current level of knowledge suggests that there are real limitations to our understanding and methods of measurement of SMD. These data suggest that we need to do a better job defining subtypes, clades or endophenotypes of SMD that reflect what we understand about phenotypic differences in enzyme systems, transporter proteins, and second messenger systems may underlie behavioral phenotypes, primary neuropsychiatric disorders, as well as differences in stress responses and pain sensitivity. (Schroeder et al., 2001).
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Additional Suggested Reading
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