Abstract
Background
Exploding head syndrome (EHS) is characterized by loud noises or a sense of explosion in the head during sleep transitions. Though relatively common, little is known about its characteristic symptoms or associated features.
Methods
A cross-sectional study of 49 undergraduates with EHS was performed. A clinical interview established diagnosis.
Results
The most common accompanying symptoms were tachycardia, fear, and muscle jerks/twitches with the most severe associated with respiration difficulties. Visual phenomena were more common than expected (27%). EHS episodes were perceived as having a random course, but were most likely to occur during wake-sleep transitions and when sleeping in a supine position. Only 11% reported EHS to a professional, and 8% of those with recurrent EHS attempted to prevent episodes.
Conclusions
EHS episodes are complex (Mean (M) = 4.5 additional symptoms), often multisensorial, and usually associated with clinically-significant fear. They are rarely reported to professionals and treatment approaches are limited.
Introduction
Exploding head syndrome is a sensory parasomnia characterized by the perception of loud noises and/or a sense of explosion in the head when transitioning to or from sleep. These noises are not associated with significant pain, but lead to abrupt arousal and feelings of fright (1). As such, EHS is an important differential diagnostic consideration for nocturnal headache disorders (e.g., hypnic headaches) (2). No objective tests for EHS currently exist (polysomnographic or otherwise), and diagnosis is established on clinical grounds. Several etiologies have been proposed, but EHS likely occurs due to transient neuronal dysfunctions in the reticular formation of the brainstem during sleep transitions (3,4).
Much about EHS remains unknown. In spite of the fact that it appears to be more common than early theorists believed (rates ranging from 10–14%) and not limited to older populations (5,6), the core features, risk factors, frequency of accompanying symptoms, and clinical impacts are not yet well established. This is likely due to the paucity of controlled research designs and the predominance of case studies in the literature. This fact, and the reasonable claim that patients with EHS rarely present for treatment (7), has made it difficult for knowledge of EHS to accrue. The present study attempts to address some of these gaps using a cross-sectional design and a sample of undergraduate students assessed between October 2013 and November 2015 at a university in the Pacific Northwest of the United States.
Hypotheses and goals
The study goals are to catalogue sounds perceived during EHS and their reported location and report the frequency and relative fear/severity levels of symptoms. It is hypothesized that EHS episodes will more commonly occur during wake-sleep transitions (3). Although existing data are inconsistent (3,8), it is also predicted that episode course will be random. Similar to other parasomnias (1), it is predicted that EHS will occur most frequently in a supine position, and hypothesized that only a minority of individuals will have reported EHS to professionals (7). Due to the frightening nature of EHS, it is additionally also predicted that some individuals will make attempts to prevent further episodes.
Methods
Necessary approvals from the university’s Institutional Review Board were secured and all subjects completed informed consent procedures. Subjects were derived from a sample of 1,125 undergraduate students participating for research credit and screened for a larger study of parasomnias and anxiety (full procedures are described in (5). Subjects endorsing sleep paralysis at screening were oversampled relative to a randomly-selected non-sleep paralysis sample throughout the study; those screening positive for EHS were oversampled during the final two months of the study.
A total of 304 subjects were assessed in person using the Exploding Head Syndrome Interview (EHSI) (5), administered by either a licensed clinical psychologist or doctoral student in clinical psychology (N = 2) trained in diagnostic interviewing and EHS. Individual cases were discussed during regular research meetings, and any diagnostic or symptomatic uncertainties were resolved through consensus. The EHSI follows current International Classification of Sleep Disorders (ICSD) criteria (1) and also assesses associated features, fear/severity levels of 19 specific symptoms derived from the limited empirical literature (e.g. (7)), patient perceptions of EHS, and information relevant for differential diagnosis. Ratings range from 0–8 and are based upon Anxiety and Related Disorders Interview Schedule (9) conventions (i.e. 4 and above are clinically significant).
A total of 59 individuals endorsed at least one EHS episode, but 10 were excluded due to subclinical symptoms (N = 4), significant pain during episodes (N = 2), or misperceptions of dream activity as EHS (N = 2). Two subjects with headache disorders mimicking EHS symptoms (primary stabbing headache = 1; headache unspecified = 1) were also excluded (10). The final sample (N = 49) was young (M = 19.71 years old, SD = 1.58) and consisted of 33 females, 15 males, and one transgender individual. The sample was diverse, with 26 Whites, seven Hispanics, five African-Americans, two Asians, one “other,” and eight endorsing multiple ethnicities. Regular medication use by subjects in the sample included analgesics (N = 3), hypnotics (N = 2), antidepressants (N = 2), benzodiazepines (N = 2), and insulin (N = 1).
EHS episode frequencies ranged widely (i.e., 1–150), with a median of 9.6 lifetime episodes. The self-reported duration of episodes was brief, with 70% lasting one second or less (median = 1.0; range = 0.5–4.0).
Results and discussions
Missing data
Subjects with missing data were excluded from relevant analyses and individual Ns are reported below.
Perceived sounds
Sounds heard during exploding head syndrome episodes.
Note: Total N is greater than 49, as several participants reported hearing more than one sound.
Sound location
Although some subjects perceived EHS sounds as emanating from the right (26%) or the left (19%), the majority (55%) experienced them bilaterally.
Frequency and severity of symptoms
Symptoms and hallucinations during exploding head syndrome episodes.
As participants at a severity level of 4 or above were excluded from the study, the maximum clinical rating for this variable was 3.5. **This column only includes those participants who reported the particular symptom.
Regarding the relative levels of fear/severity, all symptoms except pain, light flashes, autoscopy, and headaches were in the clinically-significant range (i.e., above 4). The experience of having to force oneself to breathe/forgetting how to breathe was associated with the highest levels of fear (i.e., “severe” to “very severe” range). The majority (67%) of headaches were reported to occur during EHS episodes as opposed to commencing afterwards.
Timing of episodes
83% of the sample reported EHS during wake-sleep transitions and 43% during sleep-wake transitions. The predominance of the former may imply that EHS is more likely to occur with attempts to inhibit auditory neurons as opposed to wakeful activation. The timing of episodes is roughly consonant with the EHS case studies summarized in (3) but, unlike this review, no EHS episodes in the present sample were reported to occur when fully awake.
Sleeping position
Similar to isolated sleep paralysis and other parasomnias (1), EHS episodes occurred most commonly in a supine (47%) as opposed to a prone (17%) or lateral recumbent (30%) position. Only 6% of the sample (N = 47) reported EHS occurring in multiple positions. Clinically, these results may imply a recommendation to not have EHS patients sleep on their back.
Episode course
Of the 44 individuals with a history of multiple episodes of EHS (90% of the total sample), episodes were reported to occur randomly (82%), in a cluster (11%), fairly regularly (5%), and regularly (2%). Clearly, these data do not indicate that reliable patterns of EHS occurrence are absent, but patients may require assistance from providers and active self-monitoring in order to identify potential triggers.
Reports to professionals
As predicted, only a fraction (11%) of the sample (N = 47) reported EHS to medical professionals. Of the five professionals EHS was reported to, one encouraged more rest, one hypothesized that the symptoms were a side effect of zolpidem, one believed that they were probably due to anxiety and “not a big deal”, and the reactions of the other two were not remembered by patients. Per patient report, no providers used diagnostic labels or were perceived to be familiar with EHS. These limited data, if robust, speak to a need for more EHS education in providers.
EHS prevention
As predicted, only a small number of individuals (8% of 47) attempted to prevent EHS, but the attempts made were reported to be effective. Of those who provided specific techniques, one took hypnotics (100% success) and two tried to increase their levels of sleep (80% and 100% effective, respectively). Clearly, more work is needed to identify useful methods for prevention. These data could support a role for behavioral interventions (e.g., improved sleep hygiene, cognitive behavioral therapy for insomnia) in addition to psychopharmacology and general clinical reassurance (3,4).
General discussion and limitations
In summary, EHS episodes were assessed in the largest sample to date using a clinical diagnostic interview. Episodes were found to be complex and fairly frightening experiences with symptom presentations that usually exceeded minimal diagnostic thresholds. These findings may provide useful information for future studies of EHS pathophysiology as well as differential diagnosis (e.g., of primary headache disorders). Further, the relatively higher frequency of abrupt visual phenomena lends additional credence to the use of a recently-proposed alternate name for EHS, episodic cranial sensory shock, as opposed to the more dramatic and auditory-focused term (12). Finally, given the fact that 17% of those initially endorsing key features of EHS criteria were subsequently excluded, it is recommended that clinical interviews be used as opposed to self-report instruments.
Limitations
Limitations of this study include the fact that subjects were exclusively derived from an undergraduate population. Though in some ways a diverse sample (e.g. ethnicity and lifetime number of episodes), it is unknown if findings will generalize to other populations (e.g., psychiatric patients) or if EHS presentations vary according to age, geographic location, or other moderating variables.
Key findings
In the largest sample to date assessed with a clinical interview, EHS symptoms were found to be distressing (i.e. creating moderate to severe levels of severity), complex (M = 4.5 additional symptoms), and frequently accompanied by visual phenomena. EHS most frequently occurred during wake-sleep transitions and in a supine position. In spite of the dramatic nature of the symptoms and strong associations with distress, EHS was rarely disclosed to medical professionals, few sufferers made attempts to prevent future episodes, and no well-established treatments are currently available.
Footnotes
Declaration of conflicting interests
The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author received no financial support for the research, authorship, and/or publication of this article.