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NEW YORK (Reuters Health) - Experiencing a mild traumatic brain injury may increase the risk of developing a sleep disorder, and a good portion of these appear to be based on disturbances in the body's normal circadian rhythm, according to the results of a new study.
"As many as 40 to 65 percent of patients with minor traumatic brain injury complain of insomnia," Dr. L. Ayalon, of the University of California, San Diego, and colleagues write in the medical journal Neurology.
In a small study of patients with minor traumatic brain injury, who were also suffering from insomnia, Ayalon's team found that about one third of the patients had circadian rhythm sleep disorders.
The researchers examined the physiologic and behavioral characteristics related to circadian rhythm in 42 patients who sustained mild traumatic brain injuries and were having problems with insomnia.
Circadian rhythm sleep disorders are disturbances in the 24-hour sleep and wake cycle, which may be related to abnormalities in neurological mechanisms or triggered by changes in an individual's schedule.
The subjects underwent a variety of tests, including melatonin and temperature measurements, and imaging tests. They were also evaluated overnight in a sleep laboratory and completed a questionnaire to determine the time of day they felt the most awake, or their "circadian preference."
Fifteen of the 42 patients (36 percent) were diagnosed with a circadian rhythm sleep disorder. Eight subjects had a delayed sleep phase syndrome and seven had an irregular sleep-wake pattern.
All eight patients with delayed sleep phase syndrome had a 24-hour regular temperature rhythm, but only four patients with irregular sleep-wake patterns displayed a similar daily rhythm.
Patients in the irregular sleep-wake pattern group also had a smaller range of 24-hour temperature rhythm compared with those in the delayed sleep phase syndrome group.
The authors note that the patients described their wake-sleep patterns that fit the clinical diagnosis they received. For example, the majority of patients diagnosed with delayed sleep phase syndrome rated themselves as "definitely an evening type," usually an indication of delayed sleep phase syndrome, Ayalon's team reports.
Conversely, patients diagnosed with an irregular sleep-wake pattern tended to classify themselves as "neither evening nor morning type," which "is most compatible with the irregular sleep-wake pattern, which lacks a clear circadian rhythm of sleep-wake cycle."
SOURCE: Neurology, April 2007.