Diagnostic co-morbidity in 2300 psychiatric out-patients presenting for treatment evaluated with a semi-structured diagnostic interview

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Abstract
Background The largest clinical epidemiological surveys of psychiatric disorders have been based on unstructured clinical evaluations. However, several recent studies have questioned the accuracy and thoroughness of clinical diagnostic interviews; consequently, clinical epidemiological studies, like community-based studies, should be based on standardized evaluations. The Rhode Island Methods to Improve Diagnostic Assessment and Services (MIDAS) project is the largest clinical epidemiological study using semi-structured interviews assessing a wide range of psychiatric disorders conducted in a general clinical out-patient practice. In the present report we examined the frequency of DSM-IV Axis I diagnostic co-morbidity in psychiatric out-patients. Method A total of 2300 out-patients were interviewed with the Structured Clinical Interview for DSM-IV (SCID) upon presentation for treatment. Results The mean number of current and lifetime DSM-IV Axis I disorders in the 2300 patients was 1.9 (s.d.=1.5) and 3.0 (s.d.=1.8) respectively. The majority of patients were diagnosed with two or more current disorders, and more than one-third were diagnosed with three or more current disorders. Examination of the most frequent current disorders in the patients with the 12 most common principal diagnoses indicated that the pattern of co-morbidity differed among the disorders. The highest mean number of current co-morbid disorders was found for patients with a principal diagnosis of post-traumatic stress disorder and bipolar disorder. Conclusions Clinicians should assume that psychiatric patients presenting for treatment have more than one current diagnosis. The pattern of co-morbidity varies according to the principal diagnosis.