Overdiagnosis of bipolar disorder among substance use disorder inpatients with mood instability.

BACKGROUND

Among substance use disorder (SUD) patients, mood instability and high-risk behaviors may suggest the presence of bipolar disorder. However, active substance abuse impedes efforts to diagnose bipolar illness validly in patients with mood complaints.

METHOD

The authors retrospectively reviewed records for 85 adults admitted sequentially over a 1-year period (August 1, 2005, to July 31, 2006) to a private inpatient dual-diagnosis unit for substance abuse/dependence and mood disorders. A senior research psychiatrist conducted diagnostic interviews based on DSM-IV criteria to ascertain current and lifetime manic or hypomanic episodes during abstinent periods.

RESULTS

Only 33% of subjects with suspected bipolar diagnoses (28/85) met DSM-IV criteria for bipolar I or II disorder. DSM-IV bipolar patients were significantly older (p = .029) and more likely to have made past suicide attempts (p = .027), abused fewer substances (p = .027), and were less likely to abuse cocaine (p < .001) than those failing to meet DSM-IV criteria. Inability to affirm bipolar diagnoses most often resulted from insufficient DSM-IV "B" symptoms associated with mania or hypomania (55% or 45/82), inability to identify abstinent periods for assessing mood symptoms (36%, 29/81), and inadequate durations of manic/hypomanic symptoms for DSM-IV syndromic criteria (12%, 10/84). Patients not meeting DSM-IV criteria were most often presumed to have bipolar disorder solely on the basis of the presence of mood instability, although this feature held little predictive value for DSM-IV bipolar diagnoses.

CONCLUSIONS

Many patients with active SUDs who are diagnosed in the community with bipolar disorder may not actually meet DSM-IV criteria for bipolar I or II disorder. Caution must be exercised when attempting to diagnose such patients, particularly when mood instability or cocaine use is present.