One of the most common symptoms found in multiple psychiatric disorders is sleep disturbance. In fact, sleep disturbance is one of the criteria for the diagnosis of major depression. This post will offer an explanation of some of the changes observed in the sleep patterns of depressed patients.
Much of this information comes from sleep studies in patients who have a diagnosis of major depressive disorder. Without getting too technical there are two primary types of sleep, non-rapid eye movement sleep (NREM) and rapid eye movement sleep (REM). The NREM sleep can be broken down further but for the sake of simplicity we will consider these two categories.
What we notice in sleep studies of patients who suffer from major depression is a much faster onset of REM sleep. The body usually cycles through these stages 4-6 times throughout the night, averaging 90 minutes in each stage. As the night progress NREM sleep decreases and REM sleep increases. A person with normal sleep architecture will enter REM after 90 minutes, in patients with depression this time period is shorter and can be observed on the sleep study results.
Other changes include decrease NREM sleep which can be thought of as restorative sleep. Increased REM density reduced total sleep time, and decreased sleep continuity are also present.
Any single change in sleep architecture is not diagnostic of major depression. However, taken together decreased onset to REM, increased REM density, and decrease sleep efficiency can separate patients with major depression from a control group.
Given all of this information, routine sleep studies are not diagnostic for major depression and are not routinely ordered unless you suspect another sleep disorder.
Hopefully this provides a basis for why questions about sleep in depressed patients are important. The sleep changes also provide some objective evidence of altered sleeping patterns in patients with depression.