Recent studies have proposed the existence of three distinct subgroups of bipolar 1 based on age at onset (AAO) (Bellivier et al. 2003: Am J Psychiatry: 160: 999–1001; Patel et al. 2006: Bipolar Disorders: 8: 91–94). The present study aims to investigate potential clinical and functional differences between these subgroups.
Participants (n = 240) were enrolled in the Bipolar Comprehensive Outcomes Study, a 2-year longitudinal observational study. Measures assessed included the Young Mania Rating Scale, Hamilton Depression Rating Scale (HAMD21), Clinical Global Impressions Scale (CGI-BP), SF-36, SLICE/Life Scale and the EuroQol. Participants were also asked about age at first major affective episode.
Our data support the existence of three subgroups; early (AAO < 20, mean = 15.47 ± 2.7) 46.5% of participants, intermediate (AAO 20–35, mean = 25.52 ± 4.4) 43.8% of participants and late (AAO > 35, mean = 46.2 ± 10.1) 9.7% of participants. The groups differed significantly in the type of first episode experienced (χ2 = 14.88, df = 1, P = 0.005) such that the early subgroup were more likely to experience a depressive first episode, while the intermediate subgroup were more likely to experience a manic first episode. At enrollment, the early subgroup reported more severe depressive symptoms [HAM-D F(1, 153) = 10.20, P = 0.007]. When the early subgroup was compared with the typical subgroup (intermediate and late combined), the early subgroup tended to experience more clinically significant distress as a result of depression (CGI-BP; χ2 = 3.73, df = 1, P = 0.053), were less satisfied with their overall health (SF-36; χ2 = 9.42, df = 4, P = 0.051) and were less able to enjoy recreational activities (SLICE; χ2 = 10.47, df = 4, P = 0.033).
Several clinical and functional differences were found between the subgroups based on preliminary data. These differences are important as they can help guide clinical management of this debilitating disorder.