Trends in diagnosis of bipolar disorder: Have the boundaries changed?

Objective: There are concerns that the diagnostic boundaries of bipolar disorder have expanded. This study seeks evidence of change in diagnostic practice at three boundaries: the 'lower' boundary with subclinical mood conditions, the 'lateral' boundary with other mental health conditions (psychotic, anxiety, substance and personality disorders) and the 'internal' boundary within affective disorders.

Methods: Diagnoses recorded in health system administrative data collections were used as a measure of clinician diagnostic behaviour. We examined all diagnoses made by public (state operated) inpatient and community mental health services in New South Wales, Australia, from 2003 to 2014.

Results: A total of 31,746 people had at least one recorded diagnosis of bipolar disorder in the period. There was a significant upward trend in the age-standardised population rate of diagnosis of bipolar disorder. Bipolar disorders made up an increasing proportion of psychosis diagnoses. There was no increase in the rate of comorbid diagnosis of bipolar disorders with non-psychotic disorders or in the likelihood of diagnosis of bipolar disorder at first or subsequent episodes of depression. There were significant reductions in diagnoses of schizophrenia, particularly in younger people.

Conclusion: There may be some increase in diagnoses of bipolar disorder in New South Wales public mental health services. However, some changes in diagnosis, particularly in younger adults, may reflect movement away from diagnoses of schizophrenia towards a range of other diagnoses, rather than specific movement towards bipolar disorder. Expansion of bipolar disorder may have been more marked in private practice settings and may have involved the poorly defined bipolar II subtype.