Rates of sleep disorder in ADHD also depend, sometimes dramatically, on how and where data are obtained. Parent checklists almost always generate high sleep symptom rates, exceeding those that can be demonstrated during formal sleep studies. Research subjects recruited in specialty clinics (such as psychiatry or sleep disorders clinics) often display both sleep and behavior problems, whereas children assessed in regular school settings exhibit fewer problems from either domain.
Further complexity arises from potential nonlinearity in the impact of sleep problems on both behavior and behavioral diagnosis. Thus, mild to moderate levels of sleepiness could produce excessive activity and reduced attention, while very high levels of sleep disturbance may cause torpor and inattention so obviously related to sleep that a separate diagnosis of ADHD would be improvident even if criteria were technically fulfilled.
For all of these reasons, the nature and extent of the relationship between ADHD and sleep remains unsettled. One widely quoted estimate for the prevalence of sleep disorders in ADHD places the rate of parent-reported sleep problems at 25% to 50% in the absence of medication.6 Spruyt and Gozal,7citing this study, give a guess-estimated rate of sleep problems in children with ADHD as 5-fold greater than that in healthy controls.
High-end estimates of sleep disorder prevalence in ADHD populations include a report from an Italian clinic that yielded polysomnography-confirmed sleep disorders, such as periodic limb movements in 40%, restless legs syndrome in 26%, SRBD in 18%, and confusional arousals in 36%.8 Findings from one study showed that 73% of children with ADHD had sleep problems and 45% of those had moderate to severe problems.9
Inconsistencies among reports have clouded interpretation of findings relative to sleep morbidity and ADHD. A recent meta-analysis produced compelling findings for both subjective and objective sleep measures in children with ADHD. In their analysis, Cortese and associates10 minimized the likelihood that comorbid conditions could account for sleep problems by excluding studies in which children were receiving pharmacological treatment or had comorbid depressive or anxiety disorders. Compared with controls, children with ADHD had significantly higher bedtime resistance and more sleep onset difficulties, night awakenings, morning wakening difficulty, sleep-disordered breathing, and daytime sleepiness. Among objective measures, sleep onset latency, stage shift frequency, and apnea-hypopnea index were increased in children with ADHD, while sleep efficiency, true sleep time, and average time to fall asleep were lower than in controls.
Notwithstanding our inability to identify true prevalence rates, studies purporting to show frequent sleep disorders are probably a fair reflection of the rate at which clinicians who see children with ADHD can expect to hear complaints of sleep problems after a careful inquiry using some combination of rating scale or checklist and interview. Children referred for diagnosis and treatment of sleep disorders or for adenotonsillectomy are likely to display psychiatric problems in which inattention, hyperactivity, or both are prominent.
Restless legs syndrome and periodic limb movements
In their meta-analyses, Sadeh and colleagues11 found that the frequency of periodic limb movements was consistently elevated in children with ADHD. The comorbidity of restless legs syndrome symptoms in ADHD has been reported to be as high as 24%.12,13 Frequent parent reports of prominent periodic limb movements, restless legs syndrome, and growing pains in their children with ADHD offer a plausible mechanistic link between sleep movement disorders and ADHD, namely, a functional dopamine(Drug information on dopamine) deficit.12 Both restless legs syndrome and periodic limb movement disorder can be successfully treated with dopamine agonists, much as ADHD usually responds to stimulant medication.
The diagnosis of restless legs syndrome is based on history and requires that the child offer some description of subjective symptoms. Children describe the discomfort that compels movement in restless legs syndrome in idiosyncratic ways; patience and creativity may be needed to understand such communications.
Most patients who experience restless legs syndrome also have periodic limb movements, although the converse is not necessarily true. In contrast to the voluntary movements of restless legs syndrome, periodic limb movements are involuntary and have a distinctively “neurological” appearance. The movements last from 0.5 to 5 seconds and recur in cycles of 5 to 90 seconds, typically in clusters, during non-REM sleep.
Both restless legs syndrome and periodic limb movement disorder can reduce the amount or quality of sleep. Restless legs syndrome prevents sleep onset and the return to sleep after awakenings at night, whereas periodic limb movement disorder may cause arousal and sleep fragmentation. Occasional limb movements are not necessarily problematic. Treatment recommendations for periodic limb movement disorder and restless legs syndrome are sleep hygiene, iron supplementation, and medications.
The elements of good sleep hygiene are presented in the Table. Common over-the-counter drugs such as antihistamines, cold preparations, and antiemetics aggravate restless legs syndrome symptoms. Recently, SSRIs have been implicated as a cause of periodic limb movements in nearly one-third of the children who receive these drugs.14
Iron deficiency, which is usually diagnosed in children as a ferritin level of 50 ng/mL or less, is associated with restless legs syndrome and periodic limb movement disorder. Small trials of iron supplementation have shown promise in children.15
The literature contains limited guidance for treating children with medications commonly recommended for adults with restless legs syndrome, such as the first-line, nonergot dopamine agonists (ropinirole and pramipexole(Drug information on pramipexole)); levodopa/carbidopa; and other agents, including clonidine(Drug information on clonidine), clonazepam(Drug information on clonazepam), opioids, and gabapentin(Drug information on gabapentin). Ropinirole(Drug information on ropinirole) and gabapentin enacarbil, a gabapentin prodrug, are the only agents approved for the restless legs syndrome indication in adults. None of these drugs have been approved or systematically studied in children. Use of dopaminergic agents may be complicated by the phenomenon of augmentation, in which symptoms begin to develop earlier in the day or spread to other parts of the body, giving rise to a condition suspiciously similar to akathisia.