Diagnosing comorbidity: concepts, criteria, and methods.

BACKGROUND The clinical and etiologic implications of comorbid psychiatric and substance-use disorders are relevant across countries and cultures. The DSM-IV now places greater emphasis on the clinical and research utility of the substance-induced disorders classification, and clarifies several important diagnostic issues specific to primary and substance-induced disorders. However, no research consensus exists over the core problem of identifying and differentiating the drug and alcohol intoxication and withdrawal symptoms that can mimic psychiatric symptoms in heavy drinkers and drug users. OBJECTIVE To investigate how various diagnostic instruments have measured comorbid psychiatric and substance-use disorders and how each instrument operationalizes the DSM-IV classification. METHOD We review the evolution of the concept of comorbidity beginning with its formalization as the 'primary-secondary' distinction in the Feighner Criteria. We address the 'organic-non-organic' distinction found in the RDC, DSM-III, and DSM-III-R; and finally, review the 'primary' and 'substance-induced' categories of DSM-IV, DSM-IV-TR and ICD-10. We describe how these distinctions have been operationalized in widely used diagnostic instruments. CONCLUSION Further understanding of these classifications and the relationship of co-occurring psychiatric and substance disorders can be accomplished with the range of available measures, particularly the Psychiatric Research Interview for Substance and Mental Disorders (PRISM), which reliably utilizes and refines DSM-IV classification distinctions.