Neuropsychologic decline precedes schizophrenia onset

By Lucy Piper, Senior medwireNews Reporter

Researchers have confirmed that neuropsychologic functioning declines in individuals with schizophrenia from before to after illness onset.

They found considerable differences in the extent and progression of this decline, however, depending on mental function. For example, for “fluid” abilities such as processing speed, learning, and executive function, deficits emerged gradually between the ages of 7 to 38 years. By contrast, deficits in “crystallized” abilities, for example verbal IQ, showed deficits by 7 years of age that remained relatively stable through midlife.

“This suggests that different pathophysiological mechanisms underlie the deficits in fluid and crystallized abilities seen in adult schizophrenia patients,” say lead researcher Terrie Moffitt (Duke University, Durham, North Carolina, USA) and colleagues.

As reported in TheAmerican Journal of Psychiatry, 31 individuals with schizophrenia who had been monitored prospectively to 38 years of age were found to have a 9-point IQ deficit in childhood (7–13 years of age), compared with more than 517 mentally healthy individuals. This increased to a 15-point deficit by adulthood (38 years of age).

This decline in IQ could not be explained by antipsychotic treatment, the researchers note, and it was specific to patients with schizophrenia, with no evidence of IQ decline seen in two comparison groups with persistent depression or mild cognitive impairment.

Neuropsychologic decline was not limited to IQ; it was evident across most mental functions, with the exception of verbal IQ and delayed memory. The greatest declines were seen for processing speed, learning, executive function, and motor function.

“Our findings suggest that neuropsychological decline in individuals with schizophrenia is nontrivial,” the researchers comment. They found that declines were one-third to three-quarters of a standard deviation unit higher than average for the control group.

Although the progression of neuropsychologic decline differed according to mental function, the findings did highlight that “a substantial proportion” of the neuropsychologic deficits in schizophrenia patients is apparent before the onset of puberty.

The researchers conclude that, given the level of neuropsychologic decline in schizophrenia patients, treatment strategies should target both neuropsychologic functioning and cognitive impairment in everyday life, in order to “have the greatest chances of success.”

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