The strong association between self-reported cannabis use and earlier onset of psychosis provides further evidence that schizophrenia may be precipitated by cannabis use and/or that the early onset of symptoms is a risk factor for cannabis use.

BackgroundMany studies have demonstrated early generalised cognitive impairment in schizophrenia.AimsTo examine executive function in first-episode schizophrenia, characterise the nature of the impairment and specify any relationships with symptoms and duration of untreated psychosis (DUP).MethodPatients (n=136) and normal controls (n=81) were assessed with the Cambridge Automated Neuropsychological Test Battery, National Adult Reading Test IQ, and Scales for the Assessment of Positive and Negative Symptoms.ResultsMemory and executive impairments in patients were independent of IQ level. Spatial working memory was impaired because of inadequate strategy use. On a planning task, patients showed reduced planning times and suboptimal problem-solving. On an attentional set-shifting task, 75% of patients were able to perform an extra-dimensional shift thought to be a core attribute of prefrontal cortex function. Those who failed had significantly longer DUP.ConclusionsPrefrontal cortex function deteriorates at the onset of psychosis and continues to worsen over time.

At illness onset, cognitive heterogeneity is present in people with schizophrenia, with a high proportion having undergone general cognitive decline. However, working memory impairment may be a common feature. Lower premorbid IQ is a risk factor for an earlier onset.

At the initiation of drug treatment, attitudes toward medication and insight appear more relevant to medication adherence than side effects. Adherence appears to reflect a complex interaction of influences, which may change over time.

Studies commonly report poor performance in psychotic patients compared with controls on tasks testing a range of cognitive functions, but, because current IQ is often not matched between these groups, it is difficult to determine whether this represents a generalized deficit or specific abnormalities. Fifty-three first-episode psychosis patients and 53 healthy controls, one-to-one matched for sex, age, and full-scale current IQ, were compared on Wechsler Adult Intelligence Scale (WAIS) subtests representing indices of perceptual organization, verbal comprehension, processing speed, and working memory as well as other tests of executive function and episodic memory. The groups showed an equivalent pattern of performance on all WAIS subtests except digit symbol processing speed, on which the patients were significantly worse. Patients were also worse on measures where performance correlated with digit symbol score, namely working and verbal memory tasks. Standardized residual scores for each subtest were calculated for each patient using the difference between their actual subtest score and a predicted subtest score based on their full-scale IQ and the performance of controls. Scaled scores and residual scores were examined for relationships with clinical measures. Digit symbol–scaled score was significantly correlated with concurrent negative syndrome score at baseline, and digit symbol residual score significantly predicted residual negative symptoms at 1-year follow-up. In summary, our comparison of patients and controls precisely matched for IQ revealed that processing speed was attenuated in recent-onset schizophrenia, contributed significantly to working and episodic memory deficits, and was a prognostic factor for poor outcome at 1 year.