(Reuters)
Updated: 2008-03-20 07:58

NEW YORK - For people predisposed to sleepwalking, keeping them awake for a full day can trigger a sleepwalking episode when they are allowed to sleep. This represents a valuable tool for diagnosing the condition, according to Canadian researchers.

They point out in the Annals of Neurology that the diagnosis of somnambulism is difficult, because sleepwalking episodes rarely occur spontaneously in the sleep laboratory. Nonetheless, sleep specialists may be called on to verify a diagnosis of somnambulism, sometimes for legal reasons, as people may unwittingly injure themselves or act aggressively while sleepwalking.

Dr. Antonio Zadra and colleagues at the University of Montreal tested the idea that restricting sleep might trigger somnambulism in a group of 40 patients thought to have the tendency to sleepwalk. Fifteen reported injuring themselves during such episodes.

The subjects first spent one normal night in the sleep lab so that typical behavior could be recorded. The next day they were supervised for 25 hours to ensure they stayed awake, and then they were allowed to sleep.

During the first night, the investigators observed 32 episodes of somnambulistic behavior in 20 subjects. Following sleep deprivation, there were 92 episodes in 36 individuals.

Sleep deprivation also increased the number of sleepwalkers who exhibited at least one complex episode -- such as sitting up or getting out of bed -- from 5 subjects the first night to 14 during recovery sleep.

Zadra's team explains that sleep deprivation does not lead to somnambulism in subjects with no history of sleepwalking, "but rather that it increases the probability of recording somnambulistic behaviors in predisposed individuals."

They caution that "the observation of behavioral events in the sleep laboratory after sleep deprivation is not in and of itself sufficient to confirm a diagnosis of somnambulism in a medicolegal context." For that, brain wave recordings with an EEG during actual episodes are needed.