Our findings indicate that children with epilepsy had slower auditory and visual reaction times, but significantly better finger tapping speed than controls. There was no significant difference in psychomotor performance between CWE on AED and the newly diagnosed counterparts yet to start AED treatment. Duration of treatment beyond 5 years was associated with better auditory reaction time. Seizure onset before 5 years of age was associated with poor auditory reaction and verbal reaction.
In the current study, CWE performed significantly worse than controls on measures of auditory and visual reaction. This finding agrees with the conclusion of Rathouz et al. [6] and Boelen et al. [4] showing longer reaction time in CWE, compared to controls. Slower reaction in CWE may be attributed to general cerebral inhibition and disruption of neural transmission by the epileptic seizure as well as the effect of anti-epileptic medications. Psychomotor impairment has also been demonstrated in newly diagnosed children around or before onset of seizure [7]. Thus psychomotor slowing in CWE might be a marker for abnormal brain development rather than the effect of seizures themselves.
An interesting observation in the present study was that finger tapping speed, a measure of hand dexterity and fine motor control, was higher in CWE compared to controls. Boelen et al. [4] also observed better fine motor control among CWE compared with control group. They, however, considered it a chance effect. It is likely that the better performance by CWE is behavioural. Tanner and colleagues have shown that intentional sub-optimal performance of tapping task can be simulated by persons motivated to perform less than optimally [16]. It may also be true that people who were more motivated to perform optimally will tap faster than those who were not. Children with epilepsy might have been more enthusiastic about the test being a part of their management than were controls. Henkin et al. [17] however, reported worse finger tapping in CWE compared to healthy controls. The reason for the difference in the current study is not clear. This observation, however, may need further investigation and possibly a prospective approach.
Anti-epileptic drug treatment may not significantly impair psychomotor function as previously suggested [8, 18,19,20,21]. In the present study, the performance of children on AED was not significantly different from the result of their counterparts who were recently diagnosed and not on AED treatment on all tests. This observation is in agreement with the findings of Boelen et al. [4] among 87 Dutch children with uncomplicated epilepsy. They observed that AEDs drug load (defined as the ratio of prescribed daily dose to defined daily dose) did not significantly affect psychomotor function in CWE. Similarly, Rathouz et al. [6] in a 6-year prospective study of 69 children with epilepsy reported that the psychomotor impairment noted at the onset of seizures did not change with treatment at 6 years follow-up. Some studies assessing psychomotor performance of CWE following discontinuation of AEDs have reported significant improvement with re-testing [22, 23]. It is probable that the improvement in psychomotor performance was due to test–retest advantage (practice effect) rather than reversal of AED-induced psychomotor slowing.
In the current study, the duration of treatment appears to be associated with improved psychomotor performance. Children who have been on AED treatment for more than 5 years had a better profile for auditory reaction than those with lesser duration of treatment. Similar observations were made with respect to visual reaction and fine motor control although both were not statistically significant. Studies on the effect of AED treatment on psychomotor performance have been inconclusive. A few authors have however, reported improvement in psychomotor abilities following commencement of AED treatment [2, 7]. It is likely, that the improvement of psychomotor function is as a result of reduced disturbance from recurrent seizures.
In the present study, psychomotor slowing was more prominent in children whose seizure started before their fifth birthday compared to those whose seizure onset was later. While this is plausible, most studies of psychomotor function in children have not considered the influence of age of onset on psychomotor performance. Younger age at onset of epilepsy has been associated with poorer cognitive function in CWE [8, 24,25,26]. Epileptiform discharges at young age could disrupt brain circuits’ formation and negatively affect neurodevelopmental processes including synaptogenesis and apoptosis [26]. These interferences would ultimately result in slow impulse generation and transmission and commonly manifest as slow reaction times. Similarly, earlier seizure may suggest more severe neuronal injury and thus greater functional abnormality.