The clinical symptoms currently used to predict a patient’s risk of future psychosis fail two-thirds of the time. Only one-in-three people identified by clinical criteria as being at risk actually developed a psychotic disorder in a three-year follow-up study. This makes the decision to prescribe, or to take, antipsychotic medications as an early preventive intervention extremely difficult since these medications carry risk of serious side effects.
The need for an accurate “biomarker” (a biological predictor) for psychosis is critical. Two-time NARSAD Grantee Daniel Mathalon, M.D., Ph.D., of the University of California, San Francisco, reports in the March 15th issue of Biological Psychiatry that he and his team may have found such a biomarker in a brain event called mismatch negativity.
Derived from scalp electroencephalography (EEG) recordings, mismatch negativity is an EEG signal that is automatically elicited from the auditory cortex and frontal lobe of the brain in response to hearing sounds that deviate from preceding sounds. The response occurs even when we are not paying attention to the sounds. Believed to reflect the ability to form short-term memory, mismatch negativity has been shown to be deficient in patients with schizophrenia.
In this study, the researchers assessed mismatch negativity in patients with schizophrenia, patients at clinically assessed high risk for psychosis and healthy controls. Mismatch negativity was deficient in the patients with schizophrenia, as expected, and also in the high-risk patients. Observed over a 12-month period, mismatch negativity was significantly reduced in those who ultimately developed a psychotic disorder.
“Our study results show that mismatch negativity deficits precede the onset of psychosis in clinical high-risk individuals, and further shows that the larger the deficit, the more imminent the risk for conversion to a psychotic disorder,” Dr. Mathalon stated. “Importantly, our study results converge with those reported by several other studies from researchers in Europe and Asia.”
Scientific Council member and Editor of Biological Psychiatry, John H. Krystal, M.D., noted, “We do not currently use tests to help us make diagnoses or to inform patients about the likely long-term course of their illness. However, this study suggests that one day it may be possible to develop this type of test.”