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Sourced from Classic Sleep Care Blog

In the early 1990s I launched a large research project to measure the impact of imagery rehearsal therapy on chronic nightmare patients, while simultaneously training to increase my clinical experience in sleep disorders medicine and completing my board certification with the AASM. It is around this time we first suspected sleep apnea was more common among insomnia patients. The more I encountered OSA/UARS patients in clinic, the more I realized the “classic” presentation of OSA did not fit the majority of patients. Instead, patients often presented with many other sleep symptoms or different types of sleep disturbance complaints, and the picture often appeared as if the individual suffered from a current psychiatric condition that perhaps was the real or primary cause of the sleep disturbance. In other words, OSA/UARS was not the obvious chief complaint in patient’s mind.

For the next two decades, we published nearly thirty research papers in opposition to the idea that the psychiatric condition is the sole cause of sleep problems. We broached the topic in the reverse order by attempting to explain how sleep disorders should be more clearly understood and treated as primary conditions, co-occurring with mental health disorders. We declared that “sleep problems as a secondary feature of psychiatric conditions” reflected a flawed and outdated model. In a new perspective, we preached the expectation that treating an independent sleep disorder would not only improve sleep but might also improve mental health. The work listed above was one of the first research articles to demonstrate that treating nightmares (a sleep disorder functioning as an independent condition) led to decreases in both sleep complaints and mental health symptoms such as anxiety, depression and posttraumatic stress.

In the 1990s and 2000s Dr. Kenneth Lichstein was among the limited number of researchers exploring this relationship. In 1999 Dr. Lichstein published one of the first articles on occult sleep apnea in elderly patients, followed by a seminal commentary in 2006 on insomnia comorbidity with the provocative title: “Secondary insomnia: a myth dismissed”. Although this paper discussed all facets of comorbidity, not just the co-occurrence of insomnia and sleep apnea, the term “comorbid insomnia” came to mean insomnia manifesting in the context of another illness while retaining an independent character requiring specific insomnia treatments. Some of the common co-occurring conditions noted were: PTSD, anxiety, depression, cancer, pain syndromes, menopausal states, chronic fatigue, fibromyalgia, post-concussive syndrome, heart conditions, neurologic conditions and so on. The list may prove to be nearly limitless when we consider how vulnerable our sleep is to any sort of medical or psychological disturbance.

We applaud the use of the comorbid insomnia terminology, because it pushes more physicians and therapists to recognize the clinical relevance of aggressively treating insomnia; whereas, in the past, many healthcare providers focused solely on treating the co-occurring condition (e.g. pain, anxiety, menopausal symptoms) with the expectation the insomnia would dissipate. Or, they offered only simplistic therapeutic approaches such as prescription or over-the-counter sleep aids, instead of referring patients for comprehensive care at sleep medical centers. Sadly, the treatment of the primary condition first and/or the use of sleep aids is still one of the most widely used practice models in medical clinics around the world. Nonetheless, among health professionals now learning about comorbid insomnia, many are gaining sufficient education to recommend evidence-based, sleep-oriented treatment approaches to a growing number of patients.

With this background, we still believe some refinement is needed in terminology, which is why we view the term complex insomnia as a better fit for many of these patients instead of comorbid insomnia. We also believe the term COMISA should be considered as well. To begin this exploration of terms, we think a most relevant analysis would determine what is the most common co-occurring condition linked to insomnia. For example, arguments could easily be made for mental health as the single most frequent comorbid condition with chronic insomnia. Reading the DSM-5 nosology handbook that lists all psychiatric disorders strongly supports this point of view, because nearly all mental health conditions include sleep disorders as criteria for the diagnosis of the psychiatric condition itself.

A potentially large flaw in the argument in favor of mental health comorbidity, however, is the presumption that psychiatric factors must be the only cause of the insomnia. And, yet this last statement is confusing, because there can be no doubt that anxiety, depression or PTSD cause or aggravate insomnia through well-documented psychophysiological factors. You can imagine that someone with any type of mental health issue must at times show some difficulties coping with life stressors; therefore it would be no surprise for poor sleep to arise as well.

Given the crucial juncture in the timetable of a psychiatric patient’s insomnia, it does not seem likely some other factor, physical or mental, could be more common as the co-occurring condition. In other words, whichever came first, insomnia or the mental health condition (or perhaps both emerge at the same time), it stands to reason the two conditions are joined at the hip….

….unless, we were to discover these patients actually have a special vulnerability to a sleep-disordered breathing condition that only emerges covertly during the inception of the patient’s sleep problems. In this hypothetical and speculative model, we are proposing sleep breathing problems are already present in a large proportion of mental health patients. Or in a corollary to this speculation, unbeknownst to these patients, they already possess a nasal or oral airway anatomy susceptible to the development of sleep breathing problems.

Let’s analyze both examples.


  1. In the first example, the mental health patient has a known sleep-breathing symptom, such as snoring, that causes mild sleep fragmentation. Add in the factor of sleep fragmentation associated with virtually any mental health condition, and at first glance this double whammy of sleep fragmentation appears to be from two seemingly unrelated sources. However, in studies dating back to 1994, Canadian researchers Sériès F, Roy N, and Marc I. were able to demonstrate that sleep fragmentation itself worsens sleep breathing. That is, sleep breathing-induced sleep fragmentation worsens breathing, and any other sort of sleep fragmentation appears to worsen sleep breathing as well. This presumably occurs through changes in the central nervous system (CNS) that affect the natural respiratory drive of the individual. Simply stated, while awake, you breathe according to one part of the CNS, and while asleep you switch to another CNS area. Obviously, these two respiratory drive systems overlap to an extent, but it seems sleep fragmentation causes a problem in how these two systems interact. Specifically, arousals and awakenings during the night (sleep frag) trigger too much alternation between the two breathing drives (waking and sleeping). This theory, while not very well researched, remains the most commonly described hypothesis among sleep experts who theorize on how someone with insomnia might develop a sleep breathing disorder.
  2. And, to quickly summarize the second scenario, potential insomniacs suffering anatomic irregularities (e.g. deviated septum, enlarged tonsils, crowded airway, large tongue, etc.) are naturally vulnerable to the future development of a sleep breathing condition. If accurate, then this individual’s sleep breathing might worsen under stress-induced sleep fragmentation.


To encapsulate the above, if breathing system vulnerability underlies insomnia problems by the interrelationship of sleep interruptions (fragmentation) and breathing events (apneas, hypopneas, flow limitations), then a new rationale would view the physical or physiological dimension to insomnia as more prominent than the psychological factor. This idea is highly relevant to clinical care when we consider current research interestson how well CBT-I works among chronic insomnia patients with known OSA/UARS. The premise of such research alleges that despite the physical sleep fragmentation of OSA/UARS, patients who learn cognitive-behavioral instructions to cope with insomnia will report fewer episodes of unwanted sleeplessness regardless of the persistence of their sleep breathing events. However, the reverse of this paradigm must also be researched once we understand the full breadth and depth of these interactions. That is, if someone with chronic insomnia is treated with PAP therapy, how much would insomnia improve despite the lack of CBT-I to change their coping skills? In both instances, questions arise as to whether residual sleep breathing events still need to be treated in patients receiving only CBT-I and whether residual insomnia behaviors still need to be treated in patients receiving only PAP therapy.

Back to the terms, I trust you see the direction taken in this post indicates a larger role for sleep breathing than the actual mental health condition, and the parsimony of the hypothesis would be upheld if chronic insomnia in pain, cancer, or cardiac patients as three examples also manifested the same nexus between sleep fragmentation and sleep breathing events. While these theories certainly warrant more research to verify or disprove the priority of sleep-disordered breathing, the selected term would convey insomnia and sleep-disordered breathing as the relevant disorders joined at the hip. If so, the COMISA term appears the most salient of the three discussed, because it is the only one to convey both disorders as in CoMorbid Insomnia Sleep Apnea.

On the surface, COMISA seems reasonable, but my concern with the term is it would be used too broadly for all patients who suffer both conditions. Why would such an approach prove problematic? COMISA might be too vague if it only functions as an umbrella term without actually conveying specific clinical relevance to a particular case. For example, although identifying a medical or psychological condition accurately with clear-cut terminology is an essential aspect of healthcare, the presentation of the disorder also plays a key part in how medical professionals recognize or treat the problem. In contrast to what is conveyed by COMISA (i.e. both conditions are present), comorbid or complex insomnia often present in varying ways based on patient perspectives, and these presentations factor a great deal in how medical professionals understand and treat a condition. In my opinion, a more incisive terminology is needed when we are dealing with insomnia patients who literally have no idea that a breathing disturbance is part of their disorder. Instead, the typical insomnia patient is more apt to report on insomnia symptoms with psychological words as in “stressed out, racing thoughts, overwhelmed,” while almost no attention would be given to breathing, let alone connecting breathing symptoms to the insomnia.

For the above reasons, when most chronic insomnia patients use the term insomnia directly or use substitute terms (e.g. horrible sleep) to describe their condition and thus appear overly focused on insomnia, I believe a better term would attend to the patient’s perspective. Thus, I favor using the word “insomnia” in the selected terminology, because most chronic insomniacs are not in a position to readily accept their condition as something caused or aggravated by a sleep breathing disorder. Instead, their mindset is more apt to believe they will require pills or psychological therapies. In the next post, I will return to our original term – “complex insomnia” – to argue why it is still the preferred way to communicate in describing these types of patients.