There is a "strong association" between epilepsy and schizophrenia, says a Danish study of more than 2 million people.

People with epilepsy had about 2.5 times the risk of schizophrenia as the general population, says the study, which is posted on BMJ Online First.

Yet that's "fairly low," says Charles Raison, MD. Most people with epilepsy probably aren't in danger of schizophrenia, he says.

Raison directs the Behavioral Immunology Clinic at Emory University's medical school. Previously, he was a consulting psychiatrist for the epilepsy service at the University of California at Los Angeles (UCLA).

Raison didn't work on the study, but he read it and put it in perspective for WebMD. He says he wasn't surprised to see a higher risk for epilepsy patients and that clinicians should consider seizures as a possible factor in psychotic patients. "I always wonder about that when we see new onset of psychosis," he says.

Read WebMD's "Newly Diagnosed with Epilepsy? Start Here"

Risk Is Still Small for Patients

The increased risk "doesn't mean that patients are going to go insane," says Raison.

He says that schizophrenia risk is very small -- about 1 percent, in general. But even with the higher risk cited in the study, people with epilepsy still have only a 2-3 in 100 chance of developing schizophrenia. "That's of some concern," says Raison, but "you can get a large increase in risk [and] if the risk is small, you're still very safe."

Put it this way, says Raison: "If I told you you had a 2.5 percent chance of winning a million bucks in the lottery, you might be excited, but you'd be an idiot to quit your job."

Read WebMD's "How is Epilepsy Treated?"

Study's Findings

The Danish study was based on records in a national database of more than 2.2 million people age 15 and older. Researchers reviewed their histories until December 2002, or until they died or were diagnosed with schizophrenia or schizophrenia-like psychosis.

Very few people (1.5 percent) had epilepsy and only a sliver of them had schizophrenia or related psychosis. Of the epilepsy patients, fewer than one in a hundred (0.8 percent) were admitted to a hospital for schizophrenia, and 1.5 percent were admitted for schizophrenia-like psychosis.

The risk was similar for men and women, and for all types of epilepsy. Age and family history of epilepsy or schizophrenia were important. The risk rose with age and was higher in those with no family history of psychosis.

Hospital treatment is free for all Danish residents, so economic factors shouldn't have interfered, say the researchers. They included Ping Qin, an associate professor at Denmark's University of Aarhus.

Read WebMD's "Epilepsy: Taming the Seizures, Dispelling the Myths"

Rare Cases

Raison says he's not surprised to see an increase in schizophrenia among epilepsy patients. "It had been part of our medical lore that some percentage of people with epilepsy would slowly, over time, develop chronic psychotic conditions," he says. There has been debate about when to call those problems schizophrenia, says Raison.

Again, those are the exceptions, not the rule. A small percentage of epilepsy patients experience psychotic symptoms during or after seizures. Those problems more often follow in the days or weeks after a seizure, and sometimes get resolved without developing into chronic conditions, says Raison.

However, it's more common for seizures to be accompanied by depression or anxiety, he says.

Of course, those problems aren't universal among epilepsy patients.

Read WebMD's "Early Epilepsy Surgery Helps Child Development"

Wiring Problem?

The findings "probably reflect an underlying link, physiologically, that we haven't figured out yet," says Raison. There may be "abnormalities in the ways neurons are wired together." Those problems may develop early in life and manifest later on, usually in early adulthood.

Future studies may address whether schizophrenia risk is higher for epilepsy patients who experience psychosis during or after seizures, he says.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: Qin, P. BMJ Online First, June 16, 2005. Charles Raison, MD, director, Behavioral Immunology Clinic; assistant professor, department of psychiatry and behavioral science, Emory University School of Medicine. News release, BMJ.