Performance on the continuous performance test in children with ADHD is associated with sleep efficiency.

ATTENTION DEFICIT HYPERACTIVITY DISORDER (ADHD), ONE OF THE MOST PREVALENT CONDITIONS IN CHILD PSYCHIATRY, MANIFESTS AS AN UNUSUALLY high and chronic level of inattention and/or impulsivity/hyperactivity. ADHD is estimated to occur in 3% to 7.5% of school-aged children and often persists into adolescence and adulthood.1 If ADHD is left untreated, affected individuals struggle with impairments in crucial areas of life.2 Several models have suggested that children with ADHD suffer from underarousal in the cortex or other CNS systems.3–5 The Continuous Performance Test (CPT) is a neuropsychological task that has repeatedly been shown to differentiate ADHD from normal groups.6 Children with ADHD show deficits in the d' parameter,7 a consensus index of arousal in the CPT.8 Additional empirical support to the hypoarousal hypothesis comes from electroencephalography (EEG) studies. These studies have shown that children with ADHD are prone to daytime hypoarousal characterized by increased theta activity (primarily in the frontal areas), decreased alpha and beta activity, and increased theta/alpha and theta/beta ratios9 compared to normal children. Sustained wakefulness and sleep deprivation causes similarly increased theta and decreased alpha activities in normal participants suggesting that insufficient sleep is associated with daytime hypoarousal. Objective studies designed to assess fatigue/alertness revealed that children with ADHD exhibited significantly more daytime sleepiness than controls.10–12 ADHD is most commonly treated with stimulant medications, such as methylphenidate (MPH). It has been suggested that psychostimulants enhance the levels of arousal in the central nervous system (CNS) and autonomic nervous system (ANS) of these individuals. Treatment with MPH and other stimulants (i.e., amphetamines) has been shown to normalize EEG patterns and to improve CPT performance13–16 in children with ADHD. These findings indicate that such medications stimulate the underaroused cortex16,17 and at least partially normalize low arousal levels,17 providing further support for the hypothesis that children with ADHD suffer from hypoarousal. Sleep problems, particularly difficulties in initiating and maintaining sleep, have been reported in an estimated 25% to 50% of children and adolescents with ADHD.18 Indeed, restless and disturbed sleep was initially included in the DSM diagnostic criteria for ADHD, though it was later excluded as being a nonspecific symptom. Parental reports indicate a 2- to 3-fold higher prevalence of sleep problems in children with ADHD compared with controls, including difficulty falling asleep, night awakenings, and restless sleep.18 Actigraphic studies have suggested that activity during sleep is higher in children with ADHD, and that these children tend to have unstable sleep patterns.18 Sleep apnea19 and restless leg syndrome (RLS)/periodic leg movement disorder (PLMD)20 have also been associated with hyperactivity and inattention. In addition, MPH and amphetamine have been found to be associated with insomnia.21 A few studies conducted with normal adult subjects have shown that stimulants enhanced performance only in fatigued individuals,22 and the impact of the medication depended on the individual's basal level of alertness or sleepiness.23–25 Several studies have examined the impact of MPH on the sleep of children with ADHD. No previous study, however, has examined whether the impact of MPH on vigilance in children with ADHD is related to the efficiency of their sleep. Given the high prevalence of sleep complaints in children with ADHD and the overlap of some ADHD symptoms with the consequences of disrupted sleep, it is important to examine whether methylphenidate increases vigilance and reverses attentional problems to different degrees in ADHD children having poor versus good sleep efficiency. In the present study, we sought to examine whether the sleep efficiency of children diagnosed with ADHD moderates their performance on the CPT and whether this is influenced by treatment with methylphenidate. We used a double-blind, placebo-controlled, within-subject (crossover) design to assess the performance of children with ADHD with different sleep efficiency, both while they were on medication and while they were on placebo. We hypothesized that the performance of children with low, but not of those with high, sleep efficiency would improve following the administration of MPH. To our knowledge, this is the first study in which the MPH response in children with ADHD has compared poor and good sleepers using an objective neuropsychological test and a validated clinical scale as the outcome measures.