A 10-year-long Scandinavian study has shed light on a small group of schizophrenic patients who suffer a greater decline in IQ over time than most patients.
Researchers at the University of Oslo and Yale have discovered that people who are diagnosed with schizophrenia often have a more positive illness trajectory than was previously thought. However, a subgroup of the study’s patients who experienced repeated psychosis after receiving treatment demonstrated significant deterioration of verbal recall and working memory ability over time. In other words, those who had a longer duration of psychosis after starting treatment saw their IQs drop more than those who experienced a shorter duration of psychosis.
These findings emphasize the need for patients at higher risk to be monitored more closely in order to detect episodes before they manifest themselves, according to secondary author and University of Oslo professor of neuropsychology Kjetil Sundet. He added that the ultimate goal in treating schizophrenic patients is to notice these warning signs before the onset of even the first psychotic episode.
So far, this study is the longest lasting of its kind to investigate whether the course of IQ is affected by duration of psychosis before treatment and duration of psychosis after treatment. Researchers found that the overall IQ of all 89 patients studied remained stable over time. But when they divided the sample into subgroups based on duration of untreated psychosis (DUP) and duration after treatment (DAT), they discovered that the length of DUP did not affect cognitive ability, while the length of DAT did correlate with cognitive decline. Patients with the longest DAT performed significantly worse on tests of intellectual ability over time compared to those with the shortest DAT. Some patients in the study saw a slight increase in IQ, which explains the overall consistency in IQ.
Additionally, the group with the longest DAT had a slightly lower baseline IQ at the start of the study than other groups, suggesting that lower IQ may indicate increased risk for a more severe course of illness.
This study was inspired by the Early Treatment and Intervention in Psychosis Study, led by co-primary investigators Svein Friis, professor of psychiatry at University of Oslo, and Thomas McGlashan, professor emeritus of psychiatry at Yale University. The main goal of that project was to find out if an Early Detection and Early Intervention program could reduce duration of untreated psychosis, and if that could improve quality of life outcomes, according to Friis.
“Without [McGlashan], this large-scale study would hardly have been possible,” Sundet said. “He inspired and enabled his colleagues to do this research.”
Although the results of this study do not provide any causal explanations of the relationship between longer illness duration after treatment and cognitive decline, the authors have offered several possible hypotheses. Because patients with greater intellectual impairments had a lower baseline IQ to begin with, they hypothesized that those patients may have possessed a lower cognitive reserve in general, hindering their ability to inhibit psychotic symptoms.
Alternatively, the researchers have proposed the existence of a distinct subtype of schizophrenia that causes more severe cognitive decline as well as longer psychotic episodes. That hypothesis is based on recent studies on certain patients’ genetic susceptibility to schizophrenia.
Though the findings of this study fall in line with previous schizophrenia-spectrum disorder studies, the study relied largely on human memory for its data, adding an element of uncertainty to the results.
According to Sundet, the general opinion of schizophrenia-spectrum disorders was much bleaker 20 years ago at the beginning of the study, when it was thought that having schizophrenia necessarily meant a major interference with normal life. However, nowadays most patients can live a good life with treatment and medication, and some people suffer only one episode their entire lives, he added.
According to the National Institute of Mental Health, schizophrenia affects 1.1 percent of the U.S. population ages 18 and older.