The sleep phenotypes of attention deficit hyperactivity disorder: the role of arousal during sleep and implications for treatment.

About 25-50% of children and adolescents with attention-deficit hyperactivity disorder (ADHD) experience sleep problems. An appropriate assessment and treatment of such problems might improve the quality of life in such patients and reduce both the severity of ADHD and the impairment it causes. According to data in the literature and to the overall complexity of the interaction between ADHD and sleep, five sleep phenotypes may be identified in ADHD: (i) a sleep phenotype characterized mainly by a hypo-arousal state, resembling narcolepsy, which may be considered a "primary" form of ADHD (i.e. without the interference of other sleep disorders); (ii) a phenotype associated with delayed sleep onset latency and with a higher risk of bipolar disorder; (iii) a phenotype associated with sleep disordered breathing (SDB); (iv) another phenotype related to restless legs syndrome (RLS) and/or periodic limb movements; (v) lastly, a phenotype related to epilepsy/or EEG interictal discharges. Each sleep phenotype is characterized by peculiar sleep alterations expressed by either an increased or decreased level of arousal during sleep that have important treatment implications. Treatment with stimulants is recommended above all in the primary form of ADHD, whereas treatment of the main sleep disorders or of co-morbidities (i.e. bipolar disorders and epilepsy) is preferred in the other sleep phenotypes. All the sleep phenotypes, except the primary form of ADHD and those related to focal benign epilepsy or focal EEG discharges, are associated with an increased level of arousal during sleep. Recent studies have demonstrated that both an increase and a decrease in arousal are ascribable to executive dysfunctions controlled by prefrontal cortical regions (the main cortical areas implicated in the pathogenesis of ADHD), and that the arousal system, which may be hyperactivated or hypoactivated depending on the form of ADHD/sleep phenotype.