In everyday linguistic usage among non-specialists, sleepiness can blend together with tiredness and fatigue. Someone might feel “tired” after climbing a mountain or chopping down a tree, while “sleepiness” is different. Emory sleep scientists explore the pathological distinctions in a paper published in Journal of Sleep Research.

A team led by neurologists Lynn Marie Trotti and David Rye has been studying idiopathic hypersomnia (IH) for several years: people who experience excessive daytime sleepiness and “sleep drunkenness,” not explained by other medical conditions.

IH’s symptoms don’t usually include persistent muscle pain or a severe response to exertion. This separates the disorder from myalgic encephalomyelitis, also known as chronic fatigue syndrome (ME/CFS). But there is some overlap, which is what neurology resident Caroline Maness, Trotti and colleagues report in the new paper. The authors use the official term SEID (systemic exertion intolerance disease), which was recommended by an Institute of Medicine panel in 2015, but hasn’t really stuck among those in the ME/CFS field.

Some people with IH have disclosed that they were previously diagnosed with ME/CFS. Outside of the sleepy vs tired issue, some people with IH report symptoms shared with ME/CFS, such as impaired circulation in their extremities in response to cold, or dizziness upon standing. Speculatively, this may point to a possible problem with the autonomic nervous system. Trotti and a collaborator at Stanford, Mitchell Miglis, are now examining this issue further.

ME/CFS has had a history of controversy. Despite its devastating impacts, some have viewed it as psychological or somehow unreal, and sufferers have felt neglected or maligned by mainstream medicine. The National Institutes of Health has made efforts to turn that situation around by investing in ME/CFS research, and there has been a surge of attention recently covering ME/CFS (Amy Maxmen items in Nature, Stanford magazine feature, Unrest documentary).

Trotti, Maness and colleagues didn’t set out to dive into ME/CFS – they explicitly label this paper a pilot study, and the results say more about the “hypersomnolent” group of patients they have been seeing for the last several years, rather than the broader ME/CFS population. The fine-grained data includes patients’ responses to questionnaires probing their post-exertional malaise, fatigue and sleepiness, along with their daily activities and ability to function.

From Maness et al, with added green vs orange color, recalling the “apples vs oranges” IH vs narcolepsy distinction. People included in this study could also report sleepiness but not have an IH diagnosis: yellow.

The patients described in the paper include those diagnosed with IH – the largest part of the group (63), as well as those with narcolepsy type 2 (25). Note: the sleep medicine field has been debating the best way to distinguish IH from narcolepsy type 2 or narcolepsy without cataplexy. The current standard, the Multiple Sleep Latency Test, measures how fast someone zonks out in a series of 5 daytime naps, and also whether someone goes into REM sleep quickly. Check out the diagnostic chart.

Others had sleepiness that remained after treatment for sleep apnea (25), didn’t get enough shut-eye time (“habitually short sleep times”, 41) or were people who didn’t fall into any of these baskets (“subjective sleepiness”, 33). In this combined group, 21 percent met criteria for SEID/ME/CFS.

Those that met criteria for SEID/ME/CFS were less likely to respond – at least temporarily – to traditional wake-promoting agents such as modafinil, methylphenidate and amphetamines: 89 vs 68 percent. However, response rates were about the same for the unconventional GABA antagonist agents being used by the Emory group: flumazenil and clarithromycin (clinical trial).

The flumazenil response rates reported in this paper are around 60 percent, corresponding well to what Trotti and Rye reported in their 2016 Journal of Clinical Sleep Medicine paper. The authors say these numbers represent patients that reported any benefit from flumazenil, regardless of whether the benefit was sustained or whether the medication was tolerable long term. The 2016 paper has a lower number (39 percent) for those that stayed with flumazenil.

Editor’s note: thanks to advice from Julie Rehmeyer.