Diagnostic stability and evolution of bipolar disorder in clinical practice: a prospective cohort study.

To evaluate the long-term stability of International Classification of Diseases-10th revision bipolar affective disorder (BD) in multiple settings.A total of 34 368 patients received psychiatric care in the catchment area of a Spanish hospital (1992-2004). The analyzed sample included patients aged > or =18 years who were assessed on > or =10 occasions and received a diagnosis of BD at least once (n = 1153; 71,543 assessments). Prospective and retrospective consistencies and the proportion of subjects who received a BD diagnosis in > or =75% of assessments were calculated. Factors related to diagnostic shift were analyzed with traditional statistical methods and Markov's models.Thirty per cent of patients received a BD diagnosis in the first assessment and 38% in the last assessment. Prospective and retrospective consistencies were 49% and 38%. Twenty-three per cent of patients received a BD diagnosis during > or =75% of the assessments.There was a high prevalence of misdiagnosis and diagnostic shift from other psychiatric disorders to BD. Temporal consistency was lower than in other studies.