BACKGROUND

The purpose of this study was to determine the clinical characteristics of patients who are diagnosed with bipolar disorder not otherwise specified (BPD NOS) and who are considered to represent part of the bipolar spectrum. The lifetime prevalence of BPD in the general population may be as high as 6% when the full spectrum of bipolar disorders is accounted for. Correct identification of true bipolar patients in clinical settings may result in more appropriate treatment. Our hypothesis was that patients with BPD NOS would be more similar to other bipolar patients than major depressive disorder (MDD) patients in terms of age of onset, history of suicidal behavior and family history of BPD.

METHODS

We conducted a retrospective chart review to extract and analyze data on the family history, disease course and clinical characteristics of 305 bipolar disorder I (BPD I), bipolar disorder II (BPD II), bipolar disorder not otherwise specified (BPD NOS) or major depressive disorder (MDD) patients who were then grouped by diagnosis for analysis. Nominal variables were compared between groups using chi-square tests and ANOVA was used to compare means between groups for continuous variables. Significant F values were followed by independent-samples t-tests.

RESULTS

Patients with BPD I, BPD II and BPD NOS were all found to have a significantly earlier mean age of onset of depression than MDD patients. A significantly higher incidence of bipolar illness in a first-degree relative was found in all BPD groups (27-32%) compared with MDD patients (11%). Only the BPD I group had a significantly higher rate of suicide attempts (42%), compared with the BPD NOS (17%) and MDD recurrent (16%) groups.

CONCLUSIONS

Our data support the conclusions of others that an early age of onset and a positive family history of bipolar illness are associated not only with BPD I and II but also with 'softer' forms of bipolar illness, which DSM-IV classifies as BPD NOS and the current literature refers to as a category of 'bipolar spectrum disorder', albeit with varying proposed definitions and diagnostic criteria. Suicide attempt history may be more useful in identifying the severity of illness than distinguishing the bipolar spectrum from depressive disorders. Further research is needed to clearly define the boundaries of the bipolar spectrum.