Insomnia appears to be a risk factor for anxiety and other psychiatric disorders.
"We know as psychiatrists that anxiety disorders produce insomnia. But now we have evidence that insomnia is a risk factor for future psychiatric disorders, in particular, anxiety disorder," Dr. John W. Winkelman said.
Anxiety disorders are the most common psychiatric disorders, affecting more than 19 million Americans per year (N. Engl. J. Med. 2005;353:803-10). In addition, insomnia is the most common sleep disorder--an estimated 10%-15% of the general population has chronic insomnia (J. Clin. Psychiatry 2005;66[Suppl. 9]:14-7).
"By no other mechanism, these would have a significant overlap, but it's not just coincidence," said Dr. Winkelman of the Sleep Health Center, Brigham and Women's Hospital, Boston.
"Often, patients with insomnia are referred to us by a primary care provider with the assumption that there is a psychiatric disorder, but 60% do not have one," Dr. Winkelman said. "But if they do, anxiety disorders are the most common."
Differential diagnosis between insomnia and anxiety can be challenging because of substantial overlap in presenting symptoms. Worry, agitation, irritability, loss of appetite, impaired concentration, loss of interest, sleep disturbance, hopelessness, and fatigue are examples. These shared signs "might tell us something about the underlying physiology," he said.
Insomnia is a presenting symptom of anxiety disorders (Clin. Ther. 2000;22[Suppl A]:A3-19). Insomnia can also be a side effect of anxiety treatment or a residual symptom after treatment (Biol. Psychiatry 1995;37:85-98). Both subjective and objective studies in generalized anxiety disorder (GAD) document increased sleep latency, decreased sleep efficiency, and decreased total sleep time, he said.
"In PTSD, things get even uglier," he said. Hypervigilance is a diagnostic criterion for posttraumatic stress disorder. Most patients will have sleep problems, including nightmares and difficulty with sleep onset and duration. "However, objectively, we have not been able to demonstrate worse sleep in people with PTSD in sleep lab studies."
Some patients with insomnia develop conditioned fear of the sleep environment. Typically, this "insomnia phobia" begins with repeated episodes of acute insomnia, and is maintained by negative associations that produce anxiety and hyperarousal. "From my perspective, this is an anxiety disorder," Dr. Winkelman said. "Perpetuating factors increase in strength, and this is where we see patients."
Whole brain hypermetabolism is present during both wake and sleep in insomniacs, he said. "There is a relationship between cognitive arousal and insomnia--we can't prove it is causal yet--but it is why cognitive-behavioral therapy is effective."
Cognitive-behavioral therapy, or CBT, helps people with insomnia fall asleep faster and stay asleep, Dr. Winkelman said, but it does not extend total sleep time. CBT gives people more confidence that they can sleep. Although CBT has a role, he added, "For the subset of people with very severe insomnia, I would start with medication to quell the situation first." He suggested use of benzodiazepines rather than antidepressants because the latter can significantly alter sleep architecture.
And insomnia might precipitate an anxiety disorder. In one study, researchers found that persistent insomnia lasting at least a year was associated with new onset of an anxiety disorder (Gen. Hosp. Psychiatry 1997;19:245-50).
These studies are only suggestive, Dr. Winkelman said, and data are not strong enough yet to establish a causal relationship. In the meantime, he said, "we should aggressively treat insomnia. It's not just a minor quality of life issue."
BY DAMIAN MCNAMARA