Bipolar disorder and its outcomes: two cohorts, 1875-1924 and 1994-2007, compared.

We compared admission rates and outcomes for bipolar disorder patients using the medical records of patients with a first hospital admission in 1875-1924 retrospectively diagnosed based on International Classification of Diseases (ICD)-10 criteria, and patients with a first admission in 1994-2007. The incidences of first admissions in the historical and contemporary periods are comparable: 1.2 and 1.3 per hundred thousand per year, respectively. Manic episodes constituted a greater proportion of admissions historically, while depressive episodes made up more in the contemporary sample. There is no evidence for a reduction in the mean inter-admission intervals with duration of illness. This study suggests that modern treatments may have decreased lengths of stay in hospital, but at a cost of contributing to more admissions. It also points to a shift in the threshold for admissions.