Cryptic Restlessness and Sleepwalking

I thank Lopez et al. for providing further insight on the topic of sleepwalking (SW), a common, occasionally injurious disorder for which there is scant therapeutic evidence.^1,2 In their letter responding to my editorial, “Darwin's Predisposition and the Restlessness that Drives Sleepwalking,”³ Lopez et al. report on their data demonstrating an absence of a link between isolated SW and clinically defined restless legs syndrome (RLS).¹ Their additional data are valuable to note, especially in light of the paucity of data regarding the etiology of this common condition.

However, Lopez et al. may have misunderstood my editorial and did not consider the wealth of data linking RLS to cases of SW induced by medications, as well as when individuals eat during their SW behaviors (sleep-related eating disorder).

Of note, I did not suggest that RLS, using current restrictive diagnostic criteria, is the predisposition of isolated SW, but instead that a more subtle form of restlessness (I described it as “cryptic motor restlessness”) could explain many cases of medication induced sleepwalking. Of note, medication-induced SW was specifically excluded from their analysis.^1–3

It is widely recognized by sleep clinicians that, while helpful, RLS diagnostic criteria fail to characterize many patients who struggle to fall asleep due to discomfort that compels them to move.^4–6 Patients will describe symptoms in innumerous ways (painful, cramping, deep itching, numbness, pulling, crawling), and not surprisingly many patients will attribute the discomfort to some other problem: “that is just my back pain” or “my diabetic neuropathy.” Others describe a restlessness not confined to the lower extremities, for example: restless arms, restless abdomen, and restless genitalia.⁶ Many patients ultimately feel that these symptoms cannot be placed into language and merely state that “there is something wrong that is compelling me to move.” Other nocturnal urges that do not fit into the strict RLS criteria have also been described, such as restless eating and restless smoking.^4,7–9 Further, commonly prescribed medications such as alpha 2-delta ligands (gabapentin, pregabalin) and opioids can mask restlessness and prevent proper diagnosis.

These patients with poorly characterized restlessness often present to a clinician and request a medication to initiate sleep. Considering how frequently these agents are dispensed (e.g., one agent, zolpidem, in one year, 2011, in one country, the United States, was prescribed more than 39 million times for 9 million individuals (Food and Drug Administration: http://fda.gov/Drugs/DrugSafety/ucm334033.htm), it is not surprising that many of these patients are given a benzodiazepine receptor agonist. These medications suppress brain activity in regions of memory and executive function and thus would be expected to unleash amnestic ambulating behavior in patients whose insomnia have restless features.⁴ It was methodologically understandable that Lopez et al. did not include patients in their series whose SW behaviors were induced with sleeping medications; however, it precludes them from concluding that RLS or more cryptic forms of restlessness are not predisposing them to sleepwalking.^1,2

Finally, several independent investigators have already linked RLS to the form of sleepwalking where individuals eat (sleep-related eating disorder [SRED]), and these individuals frequently respond to RLS treatments.^4,7,9–11 While current ICSD-3 criteria separate SW from SRED, recent reports reveal an overlap between these two conditions.¹² Both conditions are NREM parasomnias arising out of N3 in the first half of the night, and 66% of patients with SRED describe comorbid sleepwalking (without eating) behaviors.¹²

I concede to Lopez et al. that RLS (strictly defined) does not appear to be linked to non-medication induced SW. However, it is still reasonable to conclude that RLS (strictly defined) is a predisposition where the subjects eat (SRED); it is also still reasonable to hypothesize that subtle motor restlessness, not enough to meet RLS criteria but enough to interfere with sleep and trigger a prescription for a sedative hypnotic agent, is a predisposition for sleepwalking as well.

Regardless, I greatly appreciate Lopez et al. contributions to our understanding of this common and occasionally injurious condition. Sleepwalking is one of the oldest reported medical conditions with untested models to base explorations of patho-physiology upon. Further studies of those who are predisposed to medication induced sleepwalking can be of great value and help provide these somnambulists with a restful, not restless, night of sleep.

CITATION

Howell M. Cryptic restlessness and sleepwalking. SLEEP 2016;39(7):1481–1482.

DISCLOSURE STATEMENT

The author has indicated no financial conflicts of interest.