Recent research shows that schizophrenia and bipolar disorder may have more in common than previously believed.

Ongoing studies by Yale faculty members Dr. Godfrey Pearlson and Dr. Amy Arnsten suggest that current standards for diagnoses are insufficient, as they are derived from a range of symptoms typically associated with both.

Currently, psychiatrists use the Diagnostic and Statistical Manual of Mental Disorders, or DSM, to diagnose patients.

“The DSM classifications were originally instituted for research diagnoses, so that when researchers did their various studies everybody would be talking about the same thing when they were making a diagnosis,” said Dr. Lorraine Siggins, the chief psychiatrist at Yale University Health Services and a clinical professor of psychiatry at the Yale School of Medicine.

In order to aid with diagnosis, the manual contains a system which tries to differentiate mental disorders based on the symptoms. However, this diagnostic method categorizes based on symptoms and not physical biological evidence, said Pearlson, a psychiatry professor at the Yale School of Medicine and director of the Olin Neuropsychiatry Research Center at the Institute of Living in Hartford.

Researchers have found overlaps between the symptoms of schizophrenia and bipolar disorder, resulting in the classification of schizoaffective disorder. Schizoaffective disorder is a diagnosis classifying conditions which exhibit some symptoms normally associated with schizophrenia and other symptoms normally associated with bipolar disorder, Siggins said.

“DSM regards schizophrenia and bipolar disorder as separate conditions but has sort of recognized that you could have an overlap in a category called schizoaffective disorder,” Pearlson said.

Pearlson’s research uses genetic profiling and neuroimaging to account for some of the overlap. His research has focused on a severe form of bipolar disorder — psychotic bipolar disorder — and characteristics it shares with schizophrenia.

“Recently we did structural studies [of the brain] using structural MRI,” Pearlson said. “We showed that the patients with psychotic bipolar disorder looked similar to schizophrenia patients, but nonpsychotic bipolar patients looked like normal controls.”

This similarity displays an overlap between the disorders and could change the practice of diagnosing bipolar disorder. Pearlson said, rather than approach bipolar disorder as a single ailment, it might be more accurate to divide it into several subtypes.

Presently, no clear, distinct classifications exist for conditions that seem to fall between schizophrenia and bipolar disorder,” said Arnsten, a professor of neurobiology at the Yale School of Medicine.

“It is a spectrum and in the middle there are patients that show symptoms of both,” she said.

The existence of similarities is supported by similar treatments of the disorders. Arnsten’s research has shown the same protein is overactive in the brains of schizophrenic and bipolar patients. This similarity helps explain why treatments that directly or indirectly affect the protein can be used to treat both disorders.