Recorded psychiatric comorbidity with bipolar disorder--a Finnish hospital discharge register study

Bipolar disorder is frequently connected to other psychiatric disorders. On the basis of The National Hospital Discharge Register in Finland, we studied the recorded prevalence of psychiatric comorbidity among bipolar inpatients by clinicians, and the factors that were associated with it. Of the 2687 hospital stays in 1998, 82% had no other recorded psychiatric diagnosis except an episode of bipolar disorder. Psychiatric comorbidity was recorded in 18% of hospital stays, of which 20% had two comorbid psychiatric diagnoses. Substance-related disorders (11%) were the most commonly recorded comorbid disorders. Personality disorders were recorded in 6%, and anxiety disorder in 1% of the hospital stays. These figures should be considered far below the expected ones. Recorded comorbidity was associated with the type of episode. Comorbidity in bipolar disorder in psychiatric hospitals in Finland seems to go greatly undetected and may have a deteriorating impact on the course of the illness.