There is no diagnostic test for DSPS and diagnosis is based on sleep history (i.e., inability to fall asleep until the middle of the night and difficulty waking up in the morning). Although DSPS is a physiological disturbance, there is no physical evidence to confirm the disorder.
Physicians often seek to exclude behavioral or lifestyle preferences, inadequate sleep hygiene, and psychophysiologic insomnia as causes for DSPS. Other sleep disorders that cause excessive daytime sleepiness, such as obstructive sleep apnea or periodic limb movement disorder (PLMD) and restless legs syndrome (RLS), also may superficially resemble delayed sleep phase syndrome.
Generally, delayed sleep phase syndrome occurs more than a few times a week for at least 1 month. Measures that can be used at home to assess sleep conditions include sleep diary and actigraphy.
A sleep diary can be used to help diagnose delayed sleep phase syndrome. Sleep diaries allow people to document late sleep onset times and delayed wake up times. The typical diary includes the following:
- Estimated sleep latency (i.e., how long it takes to fall asleep)
- Number of awakenings during the night
- Length of these awakenings
- Number of times the person gets out of bed
- Total sleep time
- How the person feels upon waking in the morning
- Number and quality of daytime naps
The diary is normally kept for a minimum of 2 weeks. It allows the patient and the physician to review sleep patterns, which may be consistent or inconsistent with DSPS.
Actigraphy, which involves wearing an inconspicuous monitoring device (usually on the wrist), also may be used in the diagnosis of DSPS. In addition to monitoring circadian rhythm, pain response, and response to medication, this device measures motion that is consistent with sleep and wake and records it throughout the night. The data is then retrieved from the device and analyzed for sleep-wake time relationships and indications of DSPS.