Diffusion tensor imaging was used to investigate cerebellar structure in children with combined epilepsy/ADHD and ADHD alone, at the University of Basel, Switzerland. By generating fractional anisotropy (FA) maps, the extent to which water diffusion is greater in one direction compared with others, the organization of white matter in the brain is computed. Healthy controls (n=12) exhibited more FA in the left and right middle cerebellar peduncle compared with 8 boys with combined epilepsy/ADHD, and more FA in the right middle cerebellar peduncle compared with 14 boys with developmental ADHD. Deficient cerebellar connections were demonstrated in both patient groups. Inattention and other ADHD problems in both epilepsy/ADHD and ADHD patients are based on the same neurobiological mechanisms that involve the middle cerebellar peduncle. 
COMMENT. One in 5 children with epilepsy has comorbid ADHD (Gross-Tsur et al, 1997). A study involving 203 patients found 60% of children with epilepsy had either ADHD-Inattentive subtype or ADHD-Combined. (Sherman EMS et al, 2007). Quality of life was impaired 2-fold in children with epilepsy complicated by ADHD-I, and 4-fold with ADHD-C comorbidity, when compared to normal controls. Impairment of attention is more likely with generalized epilepsies than with focal epilepsies, in most studies.
Approximately one in 4 children with ADHD has an abnormal EEG, without clinical seizures. The significance of subclinical seizure discharges in children with ADHD is controversial. In addition to EEG abnormalities, a neurobiological basis for ADHD is also demonstrated by MRI brain volume studies, PET studies, and neurological soft signs. MRI volumetric studies have found decreased volume of the total brain, right prefrontal cortex, cerebellar vermis, corpus callosum, and basal ganglia . These developmental abnormalities correlate with fronto-striatal-cerebellar circuit dysfunction, neuropsychological deficits, and response to stimulant medication.