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.