Introduction Attention-deficit/hyperactivity Disorder (adhd) Is among the Most Common of the Psychological Dis- Orders Affecting School-aged Children, with Prevalence Estimates Ranging

ATTENTION-DEFICIT/HYPERACTIVITY DISORDER (ADHD) IS AMONG THE MOST COMMON OF THE PSYCHOLOGICAL DISORDERS AFFECTING SCHOOL-AGED CHILDREN, WITH PREVALENCE ESTIMATES RANGING FROM 4% TO 12%.1 The cardinal features of ADHD include inattention, hyperactivity, and impulsivity. The pathophysiology of ADHD is not yet well understood but may involve abnormal functioning of dopaminergic, glutamatergic, and other neurotransmitter systems in the prefrontal cortex and additional brain regions.2,3 There are also reports of reduced regional brain volume in children with ADHD relative to healthy controls, with the volume reduction in some brain areas correlated with symptom severity.3 The Diagnostic and Statistical Manual, Fourth Edition (DSM-IV) identifies 3 subtypes of ADHD: Predominantly Inattentive Type (ADHD-I), Predominantly Hyperactive-Impulsive Type (ADHD-HI), and Combined Type (ADHD-C).4 Children with ADHD-I have greater problems with persistence of effort and sustained attention than would be expected for normal children of the same age and sex. Children with ADHD-HI have greater difficulties with excessive and inappropriate activity and with impulse control. Children with ADHD-C meet diagnostic criteria for both ADHD-I and ADHD-HI. Subtype classification of ADHD has been a controversial issue. One of several concerns is that ADHD-I may not actually be a subtype of ADHD but, rather, a separate clinical entity.5 Children with sleep disorders characterized by inadequate or poor quality sleep display ADHD-like symptoms.6-10 A recent review of research on childhood obstructive sleep apnea syndrome by a subcommittee of the American Academy of Pediatrics11 led to the conclusion that sleep-disordered breathing is associated with an almost 3-fold increase in cognitive and behavioral abnormalities, including hyperactivity, inattention, and sleepiness. Interestingly, in several of the reviewed studies, snoring was found to be a significant factor. Chronic snoring in children is a symptom of obstructive sleep apnea syndrome and other forms of sleep-disordered breathing12 but may occur independently. In a recent study of snoring and hyperactivity in a general pediatric sample, 22% of habitual snorers versus 12% of nonhabitual snorers had a clinically significant elevation on a standardized measure of hyperactivity.13 Overlap in the cognitive and behavioral symptoms of ADHD and sleep-related breathing disorders has led some investigators to suggest that breathing disorders may underlie ADHD diagnosis in a significant number of cases.14,15 For instance, Chervin and colleagues14 found that habitual snoring (snoring more than half the time) was more common among children diagnosed with ADHD (33%) than among control children from a psychiatry clinic and a pediatric clinic (9% and 11%, respectively). The authors concluded that, “If a causal effect is present,...25% of all children with ADHD could have their ADHD eliminated if their habitual snoring and any associated SRBD [sleep-related breathing disorder] were effectively treated.”14p1185 Further research on this relationship is needed. One important issue is whether nocturnal breathing disturbances are related to each of the ADHD subtypes. Because the majority of studies reviewed in the American Academy of Pediatrics’ report11 and other studies16 indicate that snoring and sleep-disordered breathing are strongly linked to hyperactivity, one might expect that nocturnal breathing disturbances would be most strongly related to ADHD with a predominant hyperactivity component. The primary purpose of this study was to determine whether chronic snoring is found in relation to each of the ADHD subtypes. Following the lead of Chervin et al,14 children with ADHD (all subtypes) were first