Objective: ADHD is one of the most common neurobehavioral disorders in childhood and involves core behavioral deficits of inattention, and/or hyperactive, impulsive behavior. The prevalence of interictal epileptiform discharges ranges from 4.9% to 60% in ADHD children without clinical seizures. The negative effect of spikes occurs in two ways: transitory interruption of cognitive function and alteration of the physiological mechanisms involved in brain plasticity and memory. A pilot study suggested that rolandic spikes were associated with increased distractibility and impulsivity in ADHD. We aimed to study the impact of epileptiform anomalies (EA)s on attention and executive functions in ADHD by comparing electroencephalography -Normal (EEG-N) and EEG-Abnormal (EEG-A) subjects. We hypothesized that EAs would alter attention and executive functions worse than they alter in EEG-A group.
Method: The sample consisted of 107 (21 female) children aged 6 to 13 years recruited by Marmara University Institute of Neurological Sciences. An inattention hyperactivity scale (IHS) is derived from 18 DSM-IV categories. A set of diagnostic criteria for symptoms of ADHD (APA 1994) was fulfilled by parents and teachers of subjects. Psychiatric assessments were made by a child and adolescent psychiatrist to determine any comorbid psychiatric condition according to DSM-IV criteria. To determine behavioural outcomes; Conners Rating Scales for parents (CPRS) and for teachers (CTRS) were used. A child neurologist made all subjects’ neurological evaluations. Wakefulness and sleep-EEG examinations were done by an 18- channel EEG. The sample was divided into two subgroups depending on the presence of EAs. EEG-N (n=68, 13 female, mean age: 8.69±2.07) and EEG-A (n=39, 8 female, mean age: 8.69±1.76). All children were administered the Wechsler Intelligence Scale for Children-Revised (WISC-R). Participants with ADHD, who were unmedicated at the time of testing, were administered a neuropsychological battery composed of Wisconsin Card Sorting Test (WCST), Stroop Color and Word Test, Category Naming and Visual Memory Span Subtest of Wechsler Memory Scale. For univariate analysis, the Student’s t test, the chi-square test and the Fisher’s exact test were used.
Results: The EEG-N and EEG-A groups were not different on demographic (age, gender, grade), comorbid psychopathologies, learning disorders, full scale, verbal and performance IQ scores and on behavioural performances (Conners’ scales), and attention and executive functions. Digit Span (DS) subtest and Stroop error correction scores were significantly (p=0.02; p=0.001 respectively) different between groups. Interestingly, EEG-A subjects had higher scores on DS subtest than EEG-N subjects and lower Stroop error correction scores.
Conclusion: On the contrary to our prediction; the co-occurance of EAs was not detrimental on attention and executive functions. Additionally, auditory/verbal working memory indexed by DS performance was higher in EEG-A group. This finding would be explained as the lower DS score is being one of cognitive endophenotypes in ADHD. Hence, EEG-N subjects might be presentation of pure, genetically determined ADHD. On the other hand, frequency of discharges and their occurrence in slow wave sleep were considered significant in worsening cognition. The effect of frequency of discharges could’t be analysed since the rate of frequent discharges in our group was low.