Reduced MMN amplitude may predict frank psychosis in ‘at risk’ patients
MedWire News: Among patients with an at-risk mental state (ARMS), mismatch negativity (MMN) amplitude alterations may help identify those who are likely to develop full-blown psychosis, say UK researchers.
Writing in the journal Schizophrenia Research, Madiha Shaikh and colleagues from King's College London observe: "Individuals with an ARMS have a 20-30% chance of developing a psychotic disorder within 2 years; however it is difficult to predict which individuals will become ill on the basis of their clinical symptoms alone."
Previous studies have shown that "direct in vivo measures of cortical activity observed in the human electroencephalogram (EEG) are useful markers of brain dysfunction in psychosis," the researchers explain.
They therefore investigated whether MMN amplitude - a change in the EEG that occurs when a novel stimulus infringes the regularity of the preceding ones - may help identify ARMS patients who are likely to subsequently develop frank psychosis.
The team enrolled 41 ARMS patients and 50 mentally healthy participants to perform a duration-deviant passive auditory oddball task whilst their EEG was recorded. The task involved listening to three blocks of 400 auditory tones, of which 85% of the tones were "standards" (25 ms duration, 5 ms rise/fall time) and 15% were "deviants" (50 ms duration, 5 ms rise/fall time).
The ARMS patients were then followed up for 2 years, and 10 (24%) subsequently developed full-blown psychosis.
The researchers found that, overall mean MMN amplitude was significantly reduced in the ARMS patients compared with controls at two (FZ and F4) of the three recording sites.
Furthermore, among the ARMS patients, those who subsequently developed full-blown psychosis had significantly lower MMN amplitude at all three recording sites (FZ, F4, and F3) compared with those who did not.
Overall, ARMS patients who subsequently converted to full-blown psychosis displayed the greatest reduction in MMN amplitude, with the non-converting ARMS patients being intermediate between converters and controls.
Shaikh and team conclude: "MMN deficits are present in people at ultra-high risk of developing psychosis, and are more pronounced in subjects that later make a transition to psychosis.
"These data suggest that alterations in MMN may be useful in helping clinicians predict which individuals are most likely to develop a psychotic disorder."
MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010
By Mark Cowen