![]() Although this enhancement of GABAergic transmission has not been shown to be causal to sleepiness or long sleep durations in patients with IH, biological plausibility is demonstrated by the known GABAergic mechanisms of sleep onset and maintenance, as well as the prominent role of GABA-A receptor agonists/modulators in the production of pharmacologic sleep and anesthesia ( 9– 12). Cerebrospinal fluid from patients with IH, and several other central disorders of hypersomnolence, has been shown to enhance activity at GABA-A receptors in vitro, in excess of that of cerebrospinal fluid from controls ( 8). Hypocretin deficiency, known to cause narcolepsy type 1, is not present in patients with IH ( 7). While presumably not all of these individuals would meet diagnostic criteria for idiopathic hypersomnia, it is clear that the symptoms of IH are not uncommon.Īs the name “idiopathic” hypersomnia implies, the pathophysiology of IH is presently unknown. Using a questionnaire-based algorithm, Ohayon et al have demonstrated that the symptom of excessive sleepiness, associated with irresistible daytime naps, multiple naps in the same day, non-restorative nocturnal sleep of at least 9 hours, or difficulty waking after sleep, is present in 0.5% of the population ( 6). As such, the true prevalence of IH is unknown. Clinic-based estimates of IH prevalence are limited by differing referral patterns and biases, such that estimates of the relative frequency of IH to narcolepsy with cataplexy vary substantially, anywhere from 1:10 to greater than 1:1 ( 1– 5). Population-based estimates of the frequency of IH are difficult to obtain, given the requirements for electrophysiologic testing and ruling out of other disorders that may cause similar symptoms. Idiopathic hypersomnia (IH) is a chronic neurologic disorder that manifests as pathologic daytime sleepiness with or without prolonged sleep durations. Even with current treatment options, quality of life and safety may remain impaired in patients with this challenging chronic disease. A substantial fraction of IH patients are refractory or intolerant to standard treatments, and different treatment strategies, employing novel therapeutics, are necessary in these cases. Modafinil is first line and supported by two randomized, controlled trials in IH patients. There are no FDA-approved treatments for IH symptoms, which are typically treated with off-label use of medications approved for narcolepsy. Diagnosis of IH involves a careful clinical history, with particular attention to the possibility of other disorders with similar symptomatology, and objective testing with actigraphy, polysomnography, and multiple sleep latency testing. Dysfunction of autonomic, inflammatory, or immune systems has been proposed, and patients with IH have been found to have an endogenous modulator of GABA-A receptors within their cerebrospinal fluid. The cause of idiopathic hypersomnia is presently unknown, although a genetic predisposition is suggested by the strong family history of similar symptoms. Idiopathic hypersomnia (IH) is a chronic neurological disorder that results in daytime sleepiness, frequently accompanied by long nocturnal or daytime sleep, unrefreshing sleep, difficulty in awakening, cognitive dysfunction, and autonomic symptoms.
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