Panic Disorder : The Search for a Cause

by Food and Drug Administration (FDA)

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Why Panic? The Search for a Cause

Unknowns cry out for answers, and so it is that researchers are trying to discover the elusive culprit responsible for panic disorder.

"There is a general difficulty in knowing how best to classify psychiatric disorders that relates in part to the difficulty in understanding their pathophysiology," says Thomas P. Laughren, M.D., of FDA's division of neuropharmacological drug products.

This may make the search a bit more complicated, but clues can appear if you know how to look for them. Thomas W. Uhde, M.D., a researcher with the National Institute of Mental Health, points to several factors he views as suggesting that there is, indeed, a biological basis for panic disorder: - It affects two to three times as many women as men. - Genetic factors appear to influence its transmission. - Attacks occur spontaneously and are different in quality from other forms of anxiety (often described by patients as totally different from anything else they've experienced). - Attacks can be induced or blocked with specific drugs. - Sleep panic attacks occur during non-dream sleep stages, and therefore are not associated with disturbed thoughts, vivid images, or dreams.

Studies have shown that injections of lactate, a chemical normally produced by the body, will induce panic attacks in people with panic disorder; but in normal individuals given the same dose, panic attacks will occur less frequently or not at all. Caffeine increases lactate and, in sufficient quantity (four to five cups), can induce panic attacks in panic-prone individuals, but not in normal control subjects.

Patti Griffith (not her real name) is convinced that caffeine precipitated her first panic attack. While out of town for a business meeting, she had drunk several cups of strong tea in the evening, had chocolates after dinner, and then drank more tea the following day at breakfast and lunch. During her meeting that day, she had a panic attack.

"All of a sudden, my heart was beating out of my chest, and I thought I was going to die," she says. "Finally, I had to go into the other room and lie still. My heart was beating irregularly and my head, chest and hands were hot and sweaty. This went on for quite some time, until I had to end the meeting and call for an ambulance."

Caffeine influences noradrenaline, a chemical messenger produced by the body that affects state of arousal and perhaps human emotion. One hypothesis is that panic disorder is caused by central nervous system "excitability" related to noradrenergic hyperactivity. Xanax and other benzodiazepines may work to block the effects of these chemical messengers.

"In studying noradrenergic activity in panic disorder patients," Uhde says, "scientists stumbled on the finding that these patients have lower levels of growth hormone than other adults, opening new areas of investigation into other avenues of treatment." It also raised questions of whether or not children also have panic disorder, and, if so, whether it could lead to short stature or other growth abnormalities.

"We have seen two children with panic disorder who have fairly significant disturbances in stature or growth velocity," Uhde says, "and we are now investigating the prevalence of panic disorder in children and its effect on growth and development."

Researchers also speculate that the underlying mechanism causing panic disorder in a subgroup of patients is increased levels of carbon dioxide. "These patients tend to be chronic hyperventilators," says Uhde. "The hyperventilation causes alterations in respiratory system sensitivities. When they relax or go to sleep, they have a lowered respiratory rate and relative increase in carbon dioxide, which sets off a panic episode much as carbon dioxide inhalation will do."

In fact, carbon dioxide inhalation-induced panic and sleep panic may be caused by the same underlying mechanism — increased exposure to carbon dioxide, says Uhde. When patients become relaxed, they seem to be more vulnerable to having a sleep panic episode.

"The current view," according to Uhde, "is that panic disorder patients need to maintain their level of arousal within a very narrow window, because if they become too relaxed or overly aroused, they are vulnerable to a panic attack."

About the Author

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.