Age at onset of bipolar disorder in a Norwegian catchment area sample.

Background: Early onset of bipolar disorder (BD) is an important clinical predictor of a more severe course and poorer outcome. A higher proportion of childhood onset BD has been reported in studies from USA compared to Europe. We investigated age at onset of first affective episode in a Norwegian sample and compared it to previous European and US findings. In addition, we examined whether age at onset influenced on time to first treatment, and if patient characteristics related to illness severity influenced age at onset.

Methods: Two hundred and twenty five BD patients were recruited consecutively mainly from psychiatric out-patient units at three major hospitals in Oslo, Norway, diagnosed using SCID-I and divided into four groups based on age at onset.

Results: Six percent of the patients had onset in childhood, 32% in adolescence, 43% in young adulthood, and 19% as adults. Average age at onset was 22.8 years (SD 9.4). There was a significantly higher age at onset and a significantly shorter time from onset to first treatment in patients with lifetime hospitalization.

Limitation: Retrospective information which could be confounded by collection bias.

Conclusion: Age at onset in our sample resembled previous European studies, but not US- or Norwegian studies. The difference in age at onset seems more related to different definitions of onset, than to hospitalization history. This highlights the importance of improving the research criteria and of using similar criteria to ascertain age at onset.