The aim of this paper is to expand our limited knowledge of SMD by presenting the findings on a case series of 42 patients. It is not intended as a revision of the DSM‐IV criteria.

Beyond these special populations little is known about stereotypies that persist beyond infancy in typically developing children. Despite its recognition in DSM‐IV, there is a dearth of information on SMD available to assist clinicians and parents. A general guide to distinguishing stereotypies from tics has been provided by Gilbert. 10 There are only four case series in the literature, three in children 1 , 11 , 12 and one in adults. 13 (Their findings are summarized below.) This lack of information about SMD has the potential to create diagnostic confusion.

Stereotypies also occur in children with developmental delay and blindness. 5 Self‐injurious behaviors are common in these populations and have been extensively studied. 6 , 7 Blind children with early onset of visual impairment typically display stereotypies that are similar to SMD patterns. 8 , 9

Repetitive movements are common in infants and young children. Over 60% of parents described their child as engaging in repetitive behaviors between the ages of 24 and 60 months. 3 Leekam et al. 4 reported that typically developing 2‐year‐olds showed every type of repetitive behavior typical of autistic spectrum disorders (ASDs).

Additional confusion exists between the episodic and usually brief patterns often called ‘nervous habits’, repetitive motor behaviors, or just ‘stereotypies’ on the one hand, and SMD, the focus of this paper, on the other. SMD involves more prolonged bouts or runs that may last for up to many minutes, such as hand‐flapping and pacing. The distinction is not always clear, and the general term ‘stereotypies’ may be applied to all.

Stereotypies are defined as involuntary, patterned, repetitive, coordinated, rhythmic, and non‐reflexive behaviors that are suppressible by sensory stimuli or distraction. 1 We all engage in stereotyped repetitive behavior sometimes (e.g. tapping our foot, playing with our fingers, rocking to music) and its manifestations vary in individuals and cultures. Concern arises when a pattern is unusually intense, prolonged, peculiar (beyond the cultural norm), self‐injurious, or interferes with normal activity. Classification is complicated by the wide range of movement types, natural histories, and individual variability. Some patterns tend to abate and others to persist; several patterns may co‐occur. In the DSM‐IV, 2 the term ‘stereotypic movement disorder’ (SMD) is used (See Table SI, published online). Definitional boundaries are unclear and could include behaviors as diverse as skin‐picking, lip‐licking, hair‐twirling, spinning, finger‐flicking, pacing, and infantile gratification patterns. Questions surround the terminology, classification, and appropriate cut‐off points for considering the pattern a disorder.

The following instruments were applied at diagnosis (but not repeated at follow‐up). Screening for developmental coordination disorder (DCD) was by means of the Developmental Coordination Disorder Questionnaire. 15 Comparison of our participants with SMD with those of Mahone et al. 1 was by use of the Stereotypy Severity Scale, a modification of the Yale Global Tic Severity Scale. 16 Other instruments used included the Strengths and Difficulties Questionnaire, 17 comprising 25 items rated by caregivers and widely used internationally, the Repetitive Behavior Scale – Revised, 18 , 19 an empirically derived caregiver report of the spectrum of different reported behaviors (including compulsions) on 43 items in six subscales, and assessment of sensory functioning by the Short Sensory Profile, 20 a 38‐item standard caregiver questionnaire. There were only two items on these scales that overlapped.

All children presented with enough intense or extensive stereotypic patterns to cause their parents (and sometimes teachers) concern. All the patients were Caucasian and none was in a family receiving social assistance. Patient histories and assessments were obtained and follow‐up (mean 4y after onset, SD 2y 10mo; range 1–13y) of 39 individuals was undertaken by direct reassessment ( n =9) or by semi‐structured telephone review ( n =30) by the senior author (RF). The SMD patterns that were the object of concern were observed in all participants, either directly or by video recording done by parents (who used their own judgment in capturing the pattern they were concerned about). The same areas covered initially at diagnosis were probed again at follow‐up (see Tables SII and SIII for follow‐up, published online). Comorbid disorders were diagnosed by clinical assessment by an experienced child psychiatrist, in conjunction with analysis of the items on the Stony Brook Child Symptom Inventory. 14

Exclusionary criteria were ASD, epilepsy, stroke, intellectual disability or marked developmental delay, and history of sensory impairment or major deprivation. When there was suspicion of ASD at initial assessment, exclusion was decided by assessment at clinics where clinicians were certified in the use of standardized assessments. This procedure was followed in only one instance, and ASD was not confirmed. Patients with tics or Tourette syndrome were not excluded, partly because our clinical experience and that of Mahone et al. 1 was of a high rate of comorbid tics in these children. No children were receiving medication for tics or for attention‐deficit–hyperactivity disorder (ADHD) at the time of diagnosis. Two children had mild cerebral palsy but the movement patterns were not part of their spasticity or choreiform movements.

Assessments were performed on 42 consecutive patients of a specialty neuropsychiatry clinic over a 9‐year period who fulfilled DSM‐IV criteria for SMD. This group consisted of 31 males (mean age 6y 3mo, SD 2y 8mo) and 11 females (mean age 6y 7mo, SD 1y 9mo). The project was approved by the UBC Behavioural Research Ethics Board, no. H05‐80712, and the Children’s and Women’s Health Centre Research Review Committee, no. CW05‐0165 (both to May 19, 2009). Formal consent forms were not used, as the procedures did not differ from those that were customary. Once data collection was started specifically for this report, all parents knew that their child’s anonymized data would be included and wanted to have a copy of the publication (one of their concerns was the paucity of available information).

The significant correlations were all non‐parametric (Spearman’s rank correlation coefficient). Comorbidity score (number of DSM‐IV diagnoses in addition to SMD) correlated with the Short Sensory Profile ( p <0.001) and the Repetitive Behavior Scale ( p =0.001). The Short Sensory Profile and Repetitive Behavior Scale were correlated ( p <0.001). The tactile category on the Short Sensory Profile correlated with the compulsive and sameness subdomains on the Repetitive Behavior Scale ( p =0.001 and <0.001 respectively). Auditory filtering on the Short Sensory Profile refers to the degree of control over distractibility caused by sounds; it is the other category that has the most significant correlation with comorbidity ( p =0.017). The Stereotypy Severity Scale correlated with the Repetitive Behavior Scale ( p =0.001) and with the Short Sensory Profile ( p =0.009). (These correlation details are shown in Table SIV, published online.) Analyses of variance were performed on associations with the Strengths and Difficulties Questionnaire. Comorbidity was associated with high ratings on the categories of emotional distress ( p =0.005, F =4.38, degrees of freedom [df]=4, η 2 =0.321), ADHD ( p =0.003, F =4.81, df=4, η 2 =0.342), impact on life ( p =0.004, F =4.63, df=4, η 2 =0.334), and behavioral disorder ( p =0.22, F =3.58, df=3, η 2 =0.221). As a measure of pattern severity, the Stereotypy Severity Scale was associated with the Strengths and Difficulties Questionnaire domains of behavioral difficulty ( p =0.041, F =2.83, df=4, η 2 =0.261), ADHD ( p =0.036, F =2.94, df=4, η 2 =0.269), and impact on life ( p =0.04, F =2.85, df=4, η 2 =0.263).

There were no interventions other than providing the parents (and sometimes the schools) with a discussion of present knowledge about SMD, responses to any questions, and the availability of follow‐up contacts as needed. Comorbid disorders, if present and problematic, were dealt with as with any other patients.

Transient interference with school performance occurred in eight children who diverted into the pattern instead of persisting with independent schoolwork at a pace considered normal, and who needed to be brought back to the task (this had resolved in four children). Teachers needed help to understand that these patterns were not seizures or deliberate misbehavior.

This was positive for stereotypy in 13 individuals. The patterns reported by parents about themselves were similar to those in SMD, but usually less obvious. A family history of tics was obtained in 13 participants, of ADHD in six, OCD or OCB in six, and mood or anxiety disorder in 12.

Comorbid disorders included ADHD in 16 participants, speech and language disorder in seven, sleep disorder in eight, and tics in 18 (of whom 11 met criteria for Tourette syndrome). Sixteen children screened positive for DCD using the Developmental Coordination Disorder Questionnaire. The mean number of comorbid disorders was 1.6 (range 0–6). In 12 individuals there was no comorbid disorder. The low rate of obsessive–compulsive disorder (OCD; two individuals) or significant sub‐threshold obsessive–compulsive behavior (OCB; three individuals) was striking.

Of the 39 participants followed for more than 6 months, manifestations had improved in 21, largely because of increasingly private performance of the pattern. In four it had ceased, and for a total of 25 it had improved. In only nine was there no improvement or the pattern was still fluctuating; in none was it clearly worse. In five others it was uncertain or too early to determine. In none had the pattern evolved into self‐injurious behavior. Many families adapt the need to perform the SMD pattern by incorporating it into workable times of the day.

Most children said they liked their stereotypies, consistent with parental reports. Many children used names (e.g. ‘imagination game,’‘bouncing,’‘exercises,’‘relaxation,’‘pacing’) and might announce that it was time to do it. Several children volunteered that the movements were associated with active daydreaming, and a few mentioned re‐running favorite movies or video games in their mind while performing the movement.

Triggers for the onset of movements were reported as excitement in 40, active daydreaming in 35, boredom in seven, and fatigue in two (interpreted in younger children by their parents). Anxiety seemed to be involved in five. Patterns were especially notable before or after school, in play, at meal times, before sleep, or while in a car. They were usually not evident during gross motor activity.

The most common patterns were hand and arm flapping in 22, pacing, running, or bouncing in 17, and complex finger or hand movements in 16. Complex movements with arms extended in front of the body occurred in seven, body and torso tensing movements in five, rocking in three, head‐banging in three, and face‐pressing in three. The movements tended to occur in extended runs or bouts sometimes lasting up to 1 hour. Facial grimacing and vocalization also occurred during bouts of SMD in 14 and 22 children respectively. All movements were easily stopped by deliberate distraction. None involved objects and none were reported to occur in sleep. The descriptive categories listed are arbitrary and cannot capture the many variations: for example, while hand‐flapping, many children simultaneously or occasionally engaged in complex finger patterns (four children), or pacing, running, or jumping (11). These were the only common combinations. Only eight children had a single pattern.

Mean age when seen for diagnosis was 6 years 4 months (SD 2y 7mo), with a range of 12 to 13 years 5 months; delay from onset was a mean of 5 years (SD 27mo). The clinical suspicions on referral were tics in 26 individuals, ASD in 10, compulsions in five, and epilepsy in one.

In 19 participants the movements began before the age of 1 year, and in 16 more in the second year. In the other six, onset was reported to be between the age of 2 and 3 years. Mean age at onset was 17 months (SD 9.4mo, range 5mo‐3y). In two it was uncertain.

Discussion

This study is the first to report that improvement is largely accounted for by a shift to performing the stereotypies in private rather than in public, and not necessarily due to a reduction in the movements per se. Gradual behavioral shaping has been described before in the stereotypies of blind children.8, 21 Over the course of several years, 33% of the series of Mahone et al.1 showed improvement. This is in marked contrast to our series, where 25 of 39 showed improvement. Although this is often a chronic pattern, as they have pointed out,1, 11 the outcome in our group is more positive, though many years may be required.

There are many similarities between our results and previous studies, including early age at onset, male predominance, and triggers of excitement and boredom. Tabulated results are shown in Table I, with comparison data from the three other childhood case series.1, 11, 12

Table I. Comparison of four studies Items Tan et al. 12 n=10) Mahone et al. 1 n=40) Harris et al. 11 n=100) Present study (n=42) Male:female ratio 7 of 10 male 63% male 62% male 31 male Follow‐up, y (SD) 3y 6mo–10y 7y 11mo (3y 6mo) 6y 10mo (5y) 4y 8mo (2y 10mo) Onset age 21mo ≤3y in 90% NA All ≤3y; mean 17mo Family history, SMD NA NA 25% 13 Lower limb involved 5/10 18% NA 22 Coursea 2/10 resolved; others unchanged 33% improved, 5% resolved, 13% worse, 50% unchanged 27% improved, 10% worse Of 39: 25 improved (4 stopped), 0 worse, 9 unchanged; 5 uncertain Triggers Excited, stressed, fascinated with visual stimuli Excitement 70%; boredom 23%. Fatigue 18%; anxiety 28% NA Excitement 40, active daydreaming 35, boredom 7, fatigue 2 Subjective No discomfort, liked it NA Excited/happy Excited/happy, liked it, facilitated fantasy Attention‐deficit–hyperactivity disorder 5/10 25% 30% 16 Tics NA 18% 18% 18 Tourette syndrome NA NA NA 11 OCD NA 5% 12% (OCD+OCB) 2 OCB NA 5% 3 Age first seen, y Median 5y 8mo 6y 8mo NA 6y 4mo Mean delay, y (SD) NA 5.7 (3) NA 5 (2y 4mo) Comorbidity (any) 2/10 NA 54% 30 Shaping In case no. 2 NA N/A 21 Vocalization 2/10 NA N/A 22 Facial grimacing NA NA 20% 14

Comorbidity Our high rates of SMD comorbidity with ADHD and tic disorders are not surprising in a clinical population that may be affected by referral bias. However, there were two unexpected findings. First, frequency of OCD and OCB was low, two and three individuals respectively (similar to the frequencies of 5% OCD and 5% OCB in Mahone et al.1), which is in contrast to Tourette syndrome, where OCD/OCB is common (48% in the Tourette syndrome international database22). This rate in SMD is low, even when compared with children with Tourette syndrome of the same age. Second, a positive screen for DCD was present in 16 participants, much higher than reported rates in the general population (a prevalence of about 5%)18 and the population with Tourette syndrome (16.7% in our clinic’s patients with Tourette syndrome). These different patterns of comorbidity suggest that SMD may involve somewhat different underlying brain mechanisms or circuits than tics.23

Differentiation of SMD from other disorders One of the most striking results of our study (consistent with previous studies) was the prolonged delay (5y) in diagnosis and the high rate of confusion with other disorders, especially tic disorders. Tics can also co‐occur with SMD, further complicating the diagnosis. The occurrence of vocalization in half and facial grimacing in one‐third of our patients with SMD makes confusion with Tourette syndrome even more likely. The important point of differentiation is that these occur as part of the SMD performance, not at other times (unless they also have tics, which are usually different in character). Although some similarities exist between SMD and tics, there are several helpful differentiating features.10 The age at onset is younger for SMD (mean 17mo, SD 9) and the range of ages at onset is narrower (5–36mo). For Tourette syndrome in our clinic (n=828), the corresponding figures are 5 years 10 months (SD 2y 4mo) and range 21 years (1–22y) in the Tourette syndrome international database.22 Severity of tics tends to increase until early adolescence,24 whereas in this study SMD gradually improved during childhood. SMD is much more likely to occur in flurries or prolonged bouts that are much longer than tics (the latter are usually brief, jerk‐like, and randomly occurring) and may be rhythmical.1 Children with tics often deny their presence and dislike their lack of control over them; tics are not given pet names. Tics in Tourette syndrome typically consist of multiple and changing types and locations, whereas SMD patterns tend to be much less variable (often single), and often more complex from the start than tics.10 It is usually clear that stereotypies occur during specifiable positive mental states, whereas with tics the association is with ‘stress’. Tics are therefore experientially quite different. OCD and OCB may also be confused with stereotypic movements and some of the patterns could look like a complex compulsive act. However, compulsions are generally associated with an underlying obsessive thought and are not experienced as pleasurable or desirable. Compulsions tend to occur during periods of anxiety whereas stereotypies tend to occur during positive excitement or boredom. Stereotypies are common in ASDs and are included in the DSM‐IV criteria for both autistic and Asperger disorders. It is our opinion based upon clinical experience that SMD movement patterns are not distinguishable from those in ASD solely by their motor description.1 Distinguishing features are the presence of abnormalities in socialization and quality of communication in ASD.25 In cases where the diagnosis is in doubt, one must examine the child’s total functioning through standardized ASD assessments. The lumping of repetitive motor behaviors with ‘restricted interests’ in the diagnostic criteria for autistic disorder and Asperger disorder has resulted in a confusing heterogeneous criterion that is probably the source of some misdiagnosis of SMD as ASD.26 Lastly, seizures are occasionally suspected but should be distinguishable from SMD by careful observation, history, as well as laboratory tests.

Clinical implications ‘If all you have is a hammer, then everything looks like a nail’, goes the old saying. If the SMD pattern is not correctly identified, it is likely that a more familiar diagnostic category, such as ASD or Tourette syndrome, may be applied. During the time the child is intensely engaged in the activity, they may appear ‘out of touch’ and therefore unsociable, increasing the likelihood of a false diagnosis of ASD. The other unfortunate outcome is to attribute all movements and vocalizations to the Tourette syndrome category. Clinical probe questions for diagnostic clarification are available in Table SII. An important question is whether these patterns are pathological, i.e. a ‘disorder,’ or are a developmental variant. Although the DSM‐IV specifies that distress or impairment in functioning must be present, the distress is usually experienced by parents or teachers, not the children. Any impairment will be more from comorbid disorders than from the movements themselves. (We should not forget the history of another repetitive behavior: masturbation was once considered pathogenic, requiring vigorous preventive and interventional efforts.) Because SMD appears to be dimensional, at what point should treatment be considered, if there were an effective treatment available? If, contrary to the common notion that stereotyped movements are purposeless, they play a developmentally useful role in some individuals, treatment might be contraindicated.27 In the case of non‐self‐injurious SMD, the encouragement of symptom tolerance, which involves clarification of meanings for family and school, and encouragement of making the pattern private may be most appropriate. In more serious cases, in the absence of specific evidence‐based and replicated interventions, behavior modification might be considered. The only treatment study of which we are aware reported that habit‐reversal therapy and differential reinforcement of other behavior was helpful for 12 highly motivated children.28 Medical follow‐up is advisable for comorbid disorders.

Research implications It would be of interest to compare these data with equivalent data from other clinical groups. It may be that comorbid ADHD is predictive of longer delay in the SMD pattern becoming private, or of greater pattern severity; however, this is at present unknown and would require a larger study with a longitudinal design. The significant correlation of the sensory items with the Repetitive Behavior Scale, Stereotypy Severity Scale, and comorbidity scales is probably an indication that sensory and motor phenomena are linked to each other and to the complexity of neurodevelopmental disorders. These associations merit further investigation, but are not in themselves surprising.