Medicine has long known that people with the brain disorder epilepsy suffer symptoms other than seizures. They also tend to experience more depression than other people. But evidence is mounting that the reverse is true, too. People with a history of depression are more likely to develop epilepsy.  The findings are expected to lead to common, better methods of treating both conditions.

The World Health Organization (WHO) estimates that 50 million people worldwide have epilepsy, a periodic overload of electrical activity in the brain, leading to unconsciousness and uncontrolled movements. Studies suggest that developing nations have twice the rate of epilepsy of industrial countries.

Its connection to depression has been noted since ancient times. The Greek physician Hippocrates reportedly observed 1,700 years ago that epileptics become melancholics.  Indeed, epileptics suffer depression not only more than healthy people, but also more than people with other chronic conditions, such as diabetes.  As a result, scientists have viewed depression as a complication of epilepsy.

But neurologist Andres Kanner of Rush-Presbyterian St. Luke's Medical Center in New York says the relationship also occurs in the other direction.

"Data from studies done in Sweden and in the United States at Columbia University show that in fact people with depression have a three-to-seven-fold higher risk of developing epilepsy," he said.

Mr. Kanner spoke at a recent Washington convention of the American Association for the Advancement of Science.

"The bi-directional relationship between depression and epilepsy is probably explained by the fact that depression, as well as epilepsy, share common biological mechanisms that may be operant in the two disorders," he added.

Such mechanisms include abnormalities in brain structures called the temporal and frontal lobes. Brain scans in the United States, Canada and Europe have revealed that these lobes are more likely to be shrunken in both epileptics and the depressed. In addition, Mr. Kanner cites rat studies that show both disorders are related to abnormal secretions of certain neurotransmitters, chemicals that carry signals between nerves in the brain.

"So it's not that depression causes epilepsy or epilepsy causes depression, but they share these common abnormalities that, in the presence of one, the other condition will be more likely to occur," he noted.

Mr. Kanner says the common biological pathways between the two conditions might explain why people with a psychiatric history often do not respond well to medication or surgery to treat seizures.

But the new understanding of the relationship is fueling work to find common treatments to improve care for both disorders. For example, University of Illinois pharmacologist Phillip Jobe says epilepsy drugs are now being used successfully to treat depression, and there is recent evidence showing that some anti-depression drugs might have anti-epileptic properties.

"We have come to recognize a crossover phenomenon," Mr. Jobe added.  "So, that has really opened an entire new field of therapeutics. We, I think, through these understandings, have the capacity to move forward in the development of treatments that are more effective, and diagnostic procedures that are amenable to use early in life, so that those people eventually then can be protected against ever experiencing these disorders."

The scientists say the research emphasizes how depression requires aggressive treatment, because patients with this mood disorder also have two to three times the risk of stroke, and increased danger of diabetes, heart attack and another brain disorder called Parkinson's.

The director of the Long Island Jewish Comprehensive Epilepsy Center in New York, Alan Ettinger, says physicians must become aware of their patients' potential psychiatric needs to better protect their health.

"I hope these studies are a wake-up call to the general medical community, and I hope it is also a call to arms to patients, who need to be much more vocal with their physicians that their psychological concerns associated with illness are attended to," he explained.

"Not treating depression will require more visits to the doctor and higher medical costs," says Andres Kanner.