Insomnia and Sleep Misperception
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Insomnia is currently defined in clinical practice entirely by the subjective report of difficulty initiating or maintaining sleep. Most population studies of sleep duration and insomnia are based on self-report. However, when objective data is available concurrently with self-report (for example, by diary), it turns out that many patients with insomnia are under-estimating how much sleep they are getting. The gold-standard objective measure of sleep is obtained with polysomnography - specifically using the combination of EEG (brain waves), EMG (muscle tone), and EOG (eye movements). Our lab and many others have shown that some degree of misperception is commonly evident. In our recent study, the average patient with insomnia symptoms who underwent polysomnography in our lab under-estimated their total sleep duration by over one hour. In some cases, the mismatch between subjective and objective sleep is extreme: the physiology data can show normal sleep for 7 hours or more, while the patient's experience is that little or no sleep has occurred. The mechanisms behind this mismatch, or misperception, remains uncertain.
Many patients are surprised to hear that they have slept more than they felt, especially in the arguably unusual environment of the sleep lab, with all of the sensors and wires attached. Some may wonder why insomnia, which is defined by subjective symptoms, should even be concerned about "objective" sleep data. Certainly those with insomnia, especially cases in which the symptoms are chronic and/or severe, describe a conscious experience similar or identical to their usual experience of wakefulness. There are several reasons to consider the importance of objective data. One is that recent literature, for the first time, suggests that the medical risks associated with insomnia symptoms are mainly associated with the subset of insomnia patients who exhibit short sleep durations by objective measures in the lab. This is important because one must weigh the risks and benefits of sleeping pills if that approach is considered for treatment of insomnia. Another consideration is that, in other aspects of medicine, we generally do not use self-reported data when objective data can be obtained. For example, although some patients may feel certain symptoms related to their blood pressure or blood sugar, we generally do not utilize diaries of self-reporting of this data; rather we use blood pressure cuffs and glucose-meters to make objective measures that guide therapy. For some reason, the experience of sleep is so personal and so "obvious" that it seems almost silly to suggest that the sensation of being awake could persist despite brain waves showing otherwise.
Many patients are surprised to hear that they have slept more than they felt, especially in the arguably unusual environment of the sleep lab, with all of the sensors and wires attached. Some may wonder why insomnia, which is defined by subjective symptoms, should even be concerned about "objective" sleep data. Certainly those with insomnia, especially cases in which the symptoms are chronic and/or severe, describe a conscious experience similar or identical to their usual experience of wakefulness. There are several reasons to consider the importance of objective data. One is that recent literature, for the first time, suggests that the medical risks associated with insomnia symptoms are mainly associated with the subset of insomnia patients who exhibit short sleep durations by objective measures in the lab. This is important because one must weigh the risks and benefits of sleeping pills if that approach is considered for treatment of insomnia. Another consideration is that, in other aspects of medicine, we generally do not use self-reported data when objective data can be obtained. For example, although some patients may feel certain symptoms related to their blood pressure or blood sugar, we generally do not utilize diaries of self-reporting of this data; rather we use blood pressure cuffs and glucose-meters to make objective measures that guide therapy. For some reason, the experience of sleep is so personal and so "obvious" that it seems almost silly to suggest that the sensation of being awake could persist despite brain waves showing otherwise.
Keeping a Diary and Interpreting Sleep Patterns
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The mainstay of insomnia assessment is the sleep diary, which may be a more accurate representation of sleep patterns than the attempts to reconstruct sleep patterns at a clinic visit. However, patients and providers alike should be mindful of the potential mismatch between the subjective experience and recollection of sleep-wake times and objective measures. The diary itself can be a clue: the lower the number of hours of sleep per night, especially if the time in bed is longer (say, 6-9hrs), the more likely there is to be misperception. The diary may offer other clues regarding causes or contributors to insomnia. For example, the person who is napping or using caffeine might not recognize the impact of these behaviors on their sleep pattern until the diary is reviewed. For some, there may be evidence of delayed sleep phase, whereby the natural tendency is to get in bed later (and sleep later), especially when the schedule allows, such as on weekends. Delayed sleep phase syndrome has distinct treatment strategies compared to insomnia, and it is important to distinguish. The specifics of a sleep diary should be dictated by the individual patient's situation, and include factors most likely to be relevant to the sleep-wake patterns. It is common to include estimates of sleep latency, and total sleep time - both of which may show evidence of misperception compared to objective data. It is also common to report the number of awakenings during the night. Interestingly, the opposite kind of mismatch happens in this case: most patients awaken 10-times more than they think they do, but they do not remember these awakenings in the night. Awakenings may be a clue of an underlying problem ranging from nocturia to periodic limb movements to sleep apnea, perhaps more importantly than a marker of unhealthy sleep per se. In any case, one must be cautious not to create an overly complex diary, which may paradoxically induce anxious thoughts about sleep, encourage clock-watching, or create undue burden for the patient.
Underlying Treatable Sleep Disorders
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Although formal polysomnography is generally not recommended for patients with insomnia, it can prove very useful in selected patients. For example, patients with insomnia are more likely to have certain treatable sleep disorders such as sleep apnea or periodic limb movements of sleep - even if they do not have typical symptoms such as snoring or restless legs. Considering OSA in the patient with insomnia is important, because occult OSA is common, and it is treatable. In addition, some of the hypnotics used to treat insomnia have the potential to worsen breathing, such as the benzodiazepines. Periodic limb movements of sleep may occur independently of restless legs syndrome. RLS is a purely clinical diagnosis, in that it does not require PSG, and RLS can contribute to insomnia symptoms. PLMS is associated with RLS, but can be found in isolation - in that case, it may be difficult to assess by history (perhaps a bed partner notices the leg movements), but can be seen easily on PSG. It should be noted that insurance is increasingly deferring sleep testing to the home - however, these devices do not typically measure limb movements, and they do not measure sleep itself, and the evidence-based guidelines state that they should not be used in patients with comorbid sleep disorders such as insomnia.
Hypnotic Drug Considerations
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Perhaps the most important factors to keep in mind in choosing among drug therapies are the pharmacokinetics, the potential to use a single agent for multiple purposes, and the potential for drug-drug interactions. Although sleeping pills are commonly prescribed, the risk-benefit balance remains surprisingly uncertain. Risks include tolerance, dependence, interactions with other medications and alcohol, fall risk, cognitive complaints, and motor vehicle accidents. There is surprisingly little data supporting medical benefit of drugs to increase sleep duration or continuity, and most clinical trials show only small changes in sleep latency and total sleep time. In fact, recent data suggests that the previously reported medical risks associated with insomnia in large self-report epidemiology studies may be attributed to the subset with objective short sleep time when tested with PSG. Despite this important development, there is no evidence that lengthening sleep duration, whether by hypnotic or cognitive therapy, improves or reverses these risk associations.
