Among people at high risk of developing psychosis, those who will shortly convert to psychosis show cognitive impairment in comparison to those who will not convert to psychosis during the next 2 years, according to a report published online in Psychiatry Research.
This impairment affects a broad range of cognitive functions, so unfortunately there is no specific dysfunction that consistently predicts conversion to psychosis, said Mariapaola Barbato, Ph.D., of the Hotchkiss Brain Institute, the University of Calgary (Alta.), and her associates.
Several studies have examined possible precursors to the development of psychosis, but their results have been conflicting. Most have found a variety of cognitive impairments that precede psychosis, but some have not.
Dr. Barbato and her colleagues assessed the issue in a multicenter longitudinal study involving 151 young patients (aged 12-21 years) who were at clinical high risk of developing psychosis and were followed for 2 years.
At baseline all of the study subjects met the Criteria of Prodromal Syndromes (COPS), as well as one of three other sets of criteria: the attenuated positive symptom syndrome, the brief intermittent psychotic symptom syndrome, or genetic risk and deterioration. These study subjects completed a battery of cognitive tests at baseline and again 6 months later.
A total of 25 patients converted to psychosis during the study.
Compared with patients who did not develop psychosis, those who did showed significant impairment on a composite measure of cognition as well as on individual tests of attention, verbal explicit memory, verbal and spatial working memory, verbal fluency, and executive function.
In addition, over time the subjects who did not develop psychosis either had a stable or improved performance on the battery of tests. "Improvement was seen on attention, processing speed, executive function, fine motor function, and spatial working memory. Interestingly, scores on verbal memory and verbal fluency were stable," which suggests that even though they didn’t develop psychosis, these subjects "continue to have deficits on two of the tasks that are typically most impaired in schizophrenia," the investigators said (Psychiatry Res. 2012 [http://dx.doi.org/10.1016/j.psychres.2012.10.013]).
"It seems as if in a [clinically high-risk] group that most likely has some impairment, there is a tendency for those who later develop a psychotic illness to have more impairment on a range of tasks. However ... we are not seeing specific tasks or domains that are consistently impaired except perhaps for memory and fluency, similar to what is reported in the schizophrenia literature," the investigators added.
This study is limited in that about 40% of the study subjects developed psychosis before undergoing the second round of cognitive testing and thus could not complete that testing or be included in parts of the analysis, Dr. Barbato and her associates said.
The investigators added that they were unable to address the issue of whether there is a point at which cognitive performance diverges from the norm in people who will later convert to psychosis, and that this question "is clearly a target for future research."
This study was supported by the National Institute of Mental Health. No financial conflicts of interest were reported.