Diagnostic Specificity of Motor Impairments: Comparison of Adults with ASD, ADHD, and Healthy Controls

Background: Neurobehavioral studies of motor abilities in ASD have potential to inform diagnostic, etiological, and translational research. Existing data suggest multi-faceted impairments in adults with ASD relative to healthy controls. However, the presence of persistent motor and neurocognitive impairments across developmental disorders suggests a need for research on the specificity of motor deficits to ASD. 

Objectives: The purpose of this study was to investigate patterns of motor performance in ASD, ADHD, and healthy controls and evaluate neurocognitive variables associated with motor proficiency and skilled motor performance.    

Methods: A motor and neurocognitive battery was administered by an inter-disciplinary team (e.g. neurology, neuropsychology).  The study enrolled a well-characterized sample of adults (18-40 years) into three groups: ASD (n=24), ADHD (n=18), and typically developing (n=22).  Participants were matched for age, gender, and IQ.  Basic fine and gross motor skills were evaluated with neurological examinations, Purdue pegboard, and reaction time.  Measures of skilled motor action included the following adult apraxia measures: the Kimura Movement Copying Test (MCT), Manual Sequencing Box (MSB), and Boston Diagnostic Aphasia Exam - Apraxia subtest (BDAE-Apraxia). In addition, measures of attention, memory, and executive function were assessed using the Cambridge Neuropsychological Test Automated Battery (CANTAB), Test of Variables of Attention Continuous Performance, and Controlled Oral Word Association (COWA). 

Results: MANOVAs indicate no group differences on a composite measure of basic motor proficiency. Yet, results show differences on skilled motor composite scores with both ASD and ADHD groups underperforming relative to healthy controls (F=12.09, df=2, p=.00). Analyses of individual motor proficiency tasks suggest adults with ASD exhibit specific impairments in gait and manual dexterity. The neurological exam identified gait abnormalities in adults with ASD, but not ADHD and healthy control groups (F=4.974, df=2 p=.01). Adults with ASD performed worse than ADHD and healthy controls on dominant, but not non-dominant hand trials of the Purdue Pegboard. Further, laterality effects were not observed for adults with ASD. Adults with ASD and ADHD did not differ on several apraxia subtests. However, significant impairments were identified on pantomime tasks requiring ideation (BDAE-Apraxia subtest, command items) in adults with ASD relative to ADHD and healthy controls (F=9.251, df=2, p<.00). ADOS social communication scores were significantly correlated with performance on the BDAE command subtest in the ASD group. Significant correlations were also found between several neurocognitive domains and performance on skilled motor actions.  

Conclusions: This study is consistent with prior findings of multiple motor impairments in adults with ASD relative to healthy controls. Previously reported findings of deficits in balance, bilateral coordination, and reaction time were only found relative to healthy controls, but not ADHD. In fact, results suggest several similarities in performance on motor tasks between ADHD and ASD adults.  Data suggest ASD-specific motor impairments present in measures of gait, lateralized motor dexterity, and ideational apraxia.  Further investigation of the relationship between ASD-specific deficits and other neurobehavioral domains (e.g. diagnostic, attention) are also indicated by these findings.