Study finds most psychiatric patients have more than one diagnosis

A new study by Rhode Island Hospital researchers reports that the majority of 2,300 psychiatry outpatients had more than one disorder when seeking treatment, and more than one-third had at least three disorders.

The study is published in the February 2008 edition of the journal Psychological Medicine.

It is the largest study to date using standardized interviews to evaluate a wide range of psychiatric disorders in a general clinical outpatient practice. Most patients had more than one diagnosis; on average, patients had 1.9 current diagnoses. Patients with principal diagnoses of posttraumatic stress disorder (PTSD) and bipolar disorder had the highest number of diagnoses.

Lead author Mark Zimmerman, M.D., director of outpatient psychiatry at Rhode Island Hospital and associate professor of psychiatry and human behavior at Brown Medical School, said, “Based on the results of this study, clinicians should assume that in outpatients presenting for the treatment of mood or anxiety problems, the patients have more than one diagnosis.”

The study also examined which disorders were the most common reasons for seeking treatment. Major depressive disorder was most common, present in nearly half of the patients, and was usually the primary reason for seeking treatment. In contrast, social phobia was the second most common diagnosis, present in approximately 25 percent of the patients. However, 95 percent of the patients diagnosed with social phobia came for treatment of another disorder.

Zimmerman noted, “For disorders like social phobia that are infrequently diagnosed as the principle disorder in clinical practice, it will be important for the next generation of treatment-efficacy studies to determine if treatment is effective when the disorder is a comorbid condition.”

Zimmerman, along with fellow researchers Joseph B. McGlinchey, Ph.D., Iwona Chelminski, Ph.D. and Diane Young, Ph.D., conclude that these results highlight the importance of conducting treatment research on patients with multiple disorders because this is the norm in clinical practice. Most treatment studies exclude patients with multiple disorders. The authors said, “We hope that by documenting the high frequency of comorbidity in clinical practice, this will provide the impetus for modifying how treatment studies are conducted to allow patients with multiple disorders to be included and to determine the outcome of comorbid disorders as well as the primary disorder that is being treated.”

The report is from the Rhode Island Hospital Methods to Improve Diagnostic Assessment and Services (MIDAS) Project, for which Zimmerman is the principal investigator. Zimmerman said, “The MIDAS project is unique in its integration of research quality diagnostic methods into a community-based outpatient practice affiliated with an academic medical center.”