Differentiating Insomnia and Depression in Chronic Pain Therapy
It is well established that chronic pain has a bidirectional relationship with insomnia—insomnia results in sleep deprivation, which leads to increased pain intensity the next day, which in turn makes it more difficult to have a good night’s sleep.1-4
Despite this relationship, insomnia typically is perceived as a secondary symptom of chronic pain. This may partially be due to how chronic pain patients express their sleep problems. It is common to hear a patient say: “I am in so much pain, so it is hard to sleep” or “Often, I wake up in the middle of the night because of the pain, and it’s hard to go back to sleep.” These complaints are legitimate.
The perception of insomnia as a secondary symptom also may be exacerbated by the fact that insomnia is a symptom of depression, which also is linked to chronic pain. Studies have shown that chronic pain is a strong predictor of the onset and maintenance of depression.5 Being constantly in pain can wear people down over time and affect mood.
Furthermore, chronic pain can limit activity, disturb sleep, and interfere with work performance, leading to depressed mood. Depression also can cause pain or exacerbate the pain experience.6 The resulting pain worsens depression, and depression intensifies the pain. Hence, a vicious cycle is created.
In terms of the insomnia-depression relationship, insomnia is listed as a symptom of depression. Depressed people may suffer from difficulty falling asleep (sleep-onset insomnia) or disturbed sleep throughout the night (sleep-maintenance insomnia). Patients with depressive symptoms often mention that they suffer from sleeplessness or that they find it hard to fall asleep.
However, although insomnia may be a predictor of depression, it is not always present with depression.7 Wilson et al found that insomnia is not always present as a symptom in chronic low back pain patients diagnosed with major depression.8 The same study demonstrated that not all chronic low back pain patients diagnosed with clinical insomnia suffer from major depression. In addition, studies evaluating a chronic musculoskeletal pain population have found that patients with severe insomnia do not always score high on depression measures and vice versa.9,10
This points to the conclusion that insomnia is a separate entity from depression in chronic pain. Rather, insomnia is comorbid with depression in chronic pain, not just a symptom of depression. This article will review insomnia and depression in the context of chronic pain, and discuss why insomnia and depression treatment in chronic pain needs to be differentiated.
Insomnia in Chronic Pain
Definition and Etiology
Over the years, insomnia has been cited as the most common sleep-related complaint.11,12 Although the term insomnia generally is used to describe difficulty initiating sleep, maintaining sleep, or having restorative sleep, there is a lack of consensus regarding what exactly constitutes insomnia, and there is no formal definition of insomnia.
There are several theories about the etiology of insomnia. One of them classifies insomnia as a disorder of hyperarousal.13 Hyperarousal may manifest as difficulty initiating and maintaining sleep at night, as well as creating a hypervigilant state during the day.14,15
Hyperarousal can be explained by physiologic and psychosocial models:
- The physiologic model suggests that metabolic rate, heart rate variability, neuroendocrine measures, and functional neuroimaging indicate higher arousal in people with insomnia compared to controls.
- The psychosocial model suggests that worry and rumination make it more difficult to initiate sleep and to return to sleep after awakening.16
Insomnia is exacerbated through conditioning.17 For example, an individual begins to associate the bedroom environment with difficulty falling asleep, which causes them to worry and be anxious, which then increases arousal. A daytime consequence of insomnia is sleepiness. To make up for this, individuals may nap during the day, which can interfere with their ability to fall asleep at night. An individual also may try to cure insomnia by going to bed too early. This behavior may be counterproductive and may heighten anxiety.
Prevalence and Consequences
Insomnia commonly is reported in chronic pain populations, with approximately 88% of chronic pain patients having some insomnia.18 Furthermore, Tang et al found that more than half of a chronic back pain population reported at least moderate insomnia.19
The presence of insomnia with chronic pain is associated with a variety of negative outcomes, such as anxiety, suicidal thoughts, more depressive symptoms, and limited daily functioning.9,20-24
Due to the high incidence of insomnia in chronic pain populations, insomnia often has been seen as a secondary symptom of chronic pain, with insomnia symptoms assumed to decrease as pain is managed. As a result, insomnia has not been set as a major target in the pain management regimen.
However, this view has gradually shifted, as new evidence has emerged pointing toward the bidirectional relationship between insomnia and chronic pain.1-4
Insomnia treatment can be grouped into pharmacologic and psychosocial interventions. Pharmacologic treatment generally includes benzodiazepines, nonbenzodiazepines, melatonin receptor agonist, and antidepressants to manage the insomnia symptoms. Psychosocial interventions can be given to modify behavioral and environmental factors that perpetuate or exacerbate insomnia.
Althought hypnotics are the most commonly prescribed medication, there are very few studies examining the use of hypnotics to treat insomnia in a chronic pain population; most of the literature is borrowed from studies conducted in primary insomnia populations.
Opioids typically are prescribed to lessen the pain, rather than to treat insomnia per se. It is expected that lessened pain will make it easier to fall asleep. However, prolonged opioid use is not advised, due to dependency issues and the potential for fracturing sleep architecture. Opioids block access to slow-wave sleep stages, thus hampering the ability to have restorative sleep.
Another class of medications used to treat insomnia in a chronic pain population is antidepressants, particularly the tricyclic antidepressants (TCAs; ie, trazodone). TCAs are preferred because they have sedating effects and thus facilitate sleep.25-27 TCAs also have another advantage: they can manage depression and serve as an adjuvant analgesic. However, dosages of TCAs like trazodone for sleep symptoms are often much lower than the dosages required to treat depression. When depression treatment is not needed, this helps reduce the “hangover” effect often caused by high-dose antidepressants. Regardless, in populations with chronic pain, insomnia, and depression, TCAs have the potential to address all 3 problems.