The performance of children with attention deficit hyperactivity disorder (ADHD) in the Movement Assessment Battery for Children test was evaluated at the Motorik Lab, Department of Woman and Child Health, Karolinska Institute, Sweden. In tasks involving motor-memory representations, a special grip object recorded forces generated by the fingertips during a precision grip-lift task. Twenty-five boys, aged 11 years, with ADHD were grouped according to the presence (ADHD+) or absence (ADHD) of movement dysfunction, and compared to a control group of 25 age-matched boys.
The ADHD+ group, with motor problems, showed deficits in grip-force control during the precision grip-lift task. They had difficulties in adapting motor output to target different weights, suggesting deficiencies in neuromotor control mechanisms, independent of ADHD symptoms. An overall high grip force output used by the ADHD+ group was a compensatory mechanism to increase grip stability, secondary to impaired tactile stimulation and sensory motor control. In the group with ADHD without motor problems, these deficits were less pronounced. 
COMMENT. Discrete deficits in motor performance, independent of core symptoms of inattention and hyperactivity, occur in children with ADHD complicated by motor problems. Subtypes of ADHD, with and without motor dysfunction, argue against the hypothesis of impaired motor control related to a common neural mechanism for ADHD.
The descriptive term, DAMP (deficiency of attention, motor control, and perception) has been introduced in Scandinavian countries to characterize children with ADHD complicated by motor and perceptual disorders. In the USA, DAMP is regarded as a combination of ADHD and DCD (developmental coordination disorder). Before the American Psychiatric Association introduced the symptom complexes of ADHD and DCD, these patients were regarded as ‘clumsy’ or having “minimal brain dysfunction (MBD),” and having subtle neurologic abnormalities on examination. The reintroduction and grading of the neurologic findings in the diagnosis of children with ADHD would introduce some objectivity to the definition of the syndrome.