A common belief that insomnia is a secondary symptom of depression when they co-occur is not supported by scientific evidence, and doctors should direct targeted diagnostic and treatment attention to both disorders, according to a narrative review published by the Medical Journal of Australia.
Up to 90% of patients with mood disorders also report difficulties initiating and/or maintaining sleep, and about 20–50% of patients with insomnia disorder report symptoms of depression, say the authors of the review, led by Dr. Alexander Sweetman, a Research Associate at the Adelaide Institute for Sleep Health at Flinders University.
“The co-occurrence of depression and insomnia is associated with reduced quality of life, greater overall morbidity, and increased health care use, compared with either depression or insomnia alone,” Dr. Sweetman and colleagues write.
“Therefore, it is critical to consider diagnostic and management approaches for patients with co-occurring depression and insomnia to improve patient outcomes and reduce health care costs.
“Depression is commonly conceptualized as the primary disorder, and the insomnia as a secondary symptom. This is evidenced by clinicians prioritizing the management of depression over insomnia, and an expectation that insomnia symptoms will abate when depression is successfully managed.”
The evidence suggests, however, that insomnia and depression should be treated as separate disorders, and the authors detailed six areas of evidence:
- Insomnia is commonly an independent disorder;
- Insomnia symptoms predict future depression;
- Treating insomnia can prevent onset of first time depression;
- Treating insomnia improves depressive symptoms;
- Insomnia symptoms may reduce response and remission to depression treatment; and,
- Depressive symptoms may impair response to insomnia treatment.
“Although it is common for primary care practitioners to conceptualize insomnia as a secondary symptom of depression, this belief is not supported by scientific evidence,” the article says.
“Instead, evidence suggests that depression and insomnia represent two comorbid disorders, which are potentially maintained by both bi-directional and functionally independent mechanisms.
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