medwireNews: The incidence of idiopathic hypersomnolence (IH) in the working population is greater than currently thought and may be equal to that of common neurological and psychiatric conditions, shows an analysis of data from the Wisconsin Sleep Cohort (WSC) study.
The findings suggest that “there is likely a sizeable discrepancy between the number of persons with IH relative to those who seek treatment,” say David Plante (University of Wisconsin-Madison, USA) and colleagues.
Prevalence estimates of IH to date have tended to be generated in sleep centers because diagnosis of the condition requires “objective in-laboratory sleep testing,” which is expensive and can take up to 20 hours or more, the researchers explain.
To provide estimates that better reflect the broader population, Plante et al used a two-tiered approach to identify cases of probable IH among participants of the WSC study, conducted from 2001 to 2011.
In the first tier of 792 eligible WSC participants who had undergone at least one clinical polysomnography (PSG) or multiple sleep latency test (MSLT), 19 patients were considered probable IH cases based on having an Epworth Sleepiness Scale (ESS) score of at least 11, a mean sleep latency on MSLT of less than 8 minutes, and fewer than two sleep-onset rapid eye movement periods (SOREMP) on aggregate measures of PSG and MSLT. Patients were excluded if they had obstructive sleep apnea, undertook shift work, or slept for fewer than 6 hours in either of the 2 days before undergoing PSG and MSLT.
For the second tier, two of the researchers reviewed the medical files of the 19 patients for medications that might affect daytime sleepiness, insufficient habitual sleep, and self-reported medical history for confounding conditions. This led to IH being ruled out in seven participants.
Thus, the prevalence of IH was estimated to be 1.5%, which the investigators say in Neurology is “on par with other common neuropsychiatric conditions such as bipolar disorder, epilepsy, and schizophrenia.”
Consistent with the diagnostic criteria, patients with IH had significantly more severe sleepiness than WSC participants without IH (mean ESS score1 4.3 vs 8.7) and were significantly more likely to report often or almost always feeling excessively sleepy in the day (58 vs 18%). This was despite average habitual and weekend sleep durations of 7.1 hours and 8.4 hours, respectively, which were similar to those of people without IH.
Sleep-onset latency was also significantly shorter among those with IH, at a mean 3.9 minutes versus 12.6 minutes for those without IH, otherwise sleep architecture was comparable with that of non-IH participants.
Plante and team also studied the longitudinal course of IH over a mean 12.1 years and found that while excessive daytime sleepiness was chronic for most patients, in four of nine patients with ESS measured after IH identification, scores fell to below the cutoff of 11, giving an approximate remission rate of 40%.
“Not only do these data provide hope for persons experiencing IH, but they also underscore the need to further study the mechanisms underlying symptomatic remission, which may provide insights into the pathophysiology of IH and novel therapeutic targets for treatment,” Plante et al comment.
They say their findings demonstrate that IH is “more common in the general population than generally assumed.”
The researchers also point out that the WSC participants were predominantly middle aged, “which is above the window of late adolescence to early adulthood during which IH is classically described as incident,” and so their prevalence estimates “could potentially underestimate the true prevalence of IH in younger age groups.”
They therefore conclude that “further efforts to identify, diagnose, and treat those impaired by IH are required to reduce the overall burden of this condition.”
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