T88. THE IMPACT OF AGE OF ONSET AND ILLNESS DURATION ON WHITE MATTER AND COGNITION TRAJECTORIES IN SCHIZOPHRENIA: A 7-YEAR FOLLOW-UP STUDY ACROSS MULTIPLE TIME-POINTS

Schizophrenia is characterized by cognitive deficits persisting throughout the illness from the first episode. These deficits may be associated with disruptions in white matter (WM) connectivity. Steeper age-related reductions in WM have been found in schizophrenia patients compared to healthy controls (HC), but it is unclear if these reductions are mainly influenced by age of illness onset, duration of illness, or an interaction between the two. Previous longitudinal studies of WM microstructure (measured with fractional anisotropy) have predominantly investigated medicated patients at two time-points and follow-up periods are generally limited to months. We aim to examine the impact of age at inclusion (in patients defined as illness onset) and time since inclusion (in patients defined as illness duration) on white matter and cognition trajectories in schizophrenia compared to healthy controls. We included 119 antipsychotic-naïve first-episode patients with an ICD-10 diagnosis of schizophrenia (mean age: 24,2 [18,2-42,6], 55 % men) and 111 matched HC (mean age: 24,2 [18,1-42,9], 54 % men) in a prospective longitudinal follow-up study. Patients and HC had completed between one and six visits with valid MRI and/or cognitive data. This resulted in a total of 791 visits (at inclusion, 6 weeks, 6 months, 1 year, 2 years, and 5–7 years). Subjects were scanned on a Philips 3T MRI scanner with a diffusion weighted sequence and examined with the Brief Assessment of Cognition in Schizophrenia (BACS). Outcome measures were mean fractional anisotropy (FA) and two cognitive measures: word fluency and processing speed. Using linear mixed models, we analyzed main effects and interaction effects of group, age at inclusion (age), time since inclusion (time), and time since inclusion squared (time^2) for FA, fluency, and processing speed, respectively. For processing speed, we found a main effect of group (p