Abstract
Background
Neurocognitive deficits may be a risk factor for, but also a result of, psychosis. Non-remitting symptoms, premorbid functioning, level of education, and socioeconomic background are known associations. A possible confounder is substance use, which is common among patients with psychosis and often accompanied by worse clinical outcomes. The literature, however shows mixed results for the effect of substance use on neurocognitive outcomes. In this project, the long-term associations of substance use with neurocognition in a representative sample of first-episode psychosis patients were investigated.
Methods
The sample consisted of 195 patients who were assessed for symptom levels, function and neurocognition at 1, 2, 5 and 10 years after first treatment. Test scores were grouped into factor-analysis based indices: Motor speed, verbal learning, visuomotor processing, verbal fluency, and executive functioning. We also used a standardized composite score of all tests. Patients were divided into four groups based on substance use patterns during the first two years of treatment: persistent users, episodic users, stop-users and non-users. Data were analyzed using linear mixed effects modelling.
Results
Gender, premorbid academic functioning and previous education came out as the strongest predictors of neurocognitive trajectories. Patients who stopped using substances within the first two years of follow-up, improved over time on motor speed and verbal learning indices, whereas the other groups did not. Longitudinal course was parallel for all four groups with regards to verbal fluency, while patients who stopped using substances had better scores compared to non-users. Persistent users demonstrated impaired visuomotor processing speed compared to non-users. Within the stop- and episodic use groups, patients with narrow schizophrenia diagnoses had poorer scores compared to patients with other diagnoses on verbal learning and on the overall composite neurocognitive index.
Discussion
This study is one of very few long-term studies on neurocognitive impairments in first episode psychosis focusing specifically on substance use. Early cessation of substance use was associated with less neurocognitive deficits and some improvement over time on some cognitive measures, indicating a milder illness course and superior cognitive reserves to draw from in recovering from psychosis.