Motor dysfunction in children with attention deficit hyperactivity disorder

Introduction: Aside from behavioral deficits, some children and adolescents with attention deficit hyperactivity disorder (ADHD) also exhibit motor abnormalities (clumsiness). Brain imaging studies have reported abnormalities of the cerebellum in ADHD. The aim of the study was to investigate if cerebellar dysfunction contributes to clumsiness in ADHD. Motor coordination and motor learning were assessed.

Methods: Children diagnosed with ADHD according to DSM-IV criteria, children with chronic surgical cerebellar lesions and age-matched controls were compared. Postural and gait abnormalities were assessed using dynamic posturography and treadmill walking. Motor learning was investigated by classical eyeblink conditioning. Volumes of the cerebellum and its major divisions were assessed based on 3D magnetic resonance images.

Results: Clinical observation revealed few and mild motor abnormalities in the ADHD group. Although balance abilities both in posture and gait appeared less in the ADHD group compared to controls, group differences did not reach significance. Most obvious abnormalities were observed in eyeblink conditioning. Although in the ADHD group acquisition of conditioned responses was better compared to the cerebellar group, it was less compared to controls. Unexpectedly, MR findings revealed a significantly larger volume of the cerebellum in the ADHD group compared to controls.

Conclusion: The underlying neural bases of clumsiness in ADHD are likely heterogeneous. The present findings provide some support that cerebellar dysfunction contributes. Findings, however, have to be confirmed in a larger study population including more ADHD subjects with motor abnormalities.