Cortical folding difference between patients with early-onset and patients with intermediate-onset bipolar disorder

Cerebral abnormalities have been detected in patients with bipolar disorder (BD). In comparison to BD with a later onset, early-onset BD has been found to have a poorer outcome. However, it is yet unknown whether neuroanatomical abnormalities differ between age-at-onset subgroups of the illness. We searched for cortical folding differences between early-onset (before 25 years) and intermediate-onset (between 25 and 45 years) BD patients. Magnetic resonance images of 22 early-onset BD patients, 14 intermediate-onset BD patients, and 50 healthy participants were analyzed using a fully automated method to extract, label, and measure the sulcal area in the whole cortex. Cortical folding was assessed by computing global sulcal indices (the ratio between total sulcal area and total outer cortex area) for each hemisphere, and local sulcal indices for 12 predefined regions in both hemispheres. Intermediate-onset BD patients had a significantly reduced local sulcal index in the right dorsolateral prefrontal cortex in comparison to both early-onset BD patients and healthy subjects, and lower global sulcal indices in both hemispheres in comparison to healthy subjects (p < 0.05, Bonferroni corrected). Brain tissue volumes did not differ between groups. This study provided the first evidence of a neuroanatomic difference between intermediate-onset and early-onset BD, which lends further support to the existence of different age-at-onset subgroups of BD.