Major depressive disorder redefined

Jul 24 2009

Researchers from Rhode Island Hospital's department of psychiatry propose that the definition for major depressive disorder (MDD) should be shortened to include only the mood and cognitive symptoms that have been part of the definition in the Diagnostic and Statistical Manual of Mental Disorders (DSM) for the past 35 years.

Their recommendation would exclude those symptoms that are currently part of the definition that may be associated with medical illness rather than depression. The proposal is based on a study that appears in the July 23 online first edition of the journal Psychological Medicine.

The current definition of major depressive disorder in the fourth edition of the DSM (DSM-IV) includes nine symptoms -- a definition that has remained essentially unchanged since the 1970s. With preparations for the fifth edition of the DSM underway, the researchers propose that there are two practical problems with the symptom criteria: the length of the definition and the difficulty in applying some of the criteria to patients with co-morbid medical illnesses. The researchers' proposal recommends a shortened list of symptom criteria that includes only low mood, loss of interest or pleasure, guilt/worthlessness, impaired concentration/indecision and suicidal thoughts. It would exclude the somatic criteria of fatigue, appetite disturbance and sleep disturbance (increased sleep or insomnia) as these may be associated with medical illnesses other than depression. Their proposal is called the "simpler definition of MDD."

Lead author Mark Zimmerman, MD, director of outpatient psychiatry at Rhode Island Hospital, says, "While the principles guiding criteria revision have not been clearly explained, we believe that existing diagnostic criteria should be revised when a conceptual problem is identified, or a more valid or simpler method of defining a disorder is developed. The reason for even considering a change to the symptom criteria for major depressive disorder after all these years is two-fold."

Zimmerman, who is also an associate professor of psychiatry and human behavior at The Warren Alpert Medical School of Brown University, continues, "First, studies have indicated that there are significant gaps in the knowledge or application of the MDD criteria among practitioners. Second, somatic criteria that are currently part of the DSM-IV definition such as fatigue or sleep or appetite disturbances are also symptoms of other medical illnesses and may not be indicative of a major depressive episode."

Under Zimmerman's direction, researchers from Rhode Island Hospital and The Warren Alpert Medical School of Brown University previously developed the simpler definition of MDD for a project known as the Rhode Island Methods to Improve Diagnostic Assessment and Services (RI MIDAS) project, an integration of research quality diagnostic methods into a community-based outpatient practice affiliated with an academic medical center.

Zimmerman says, "In our previous report from the RI MIDAS project, we developed a briefer list of the symptom criteria of MDD that was composed entirely of the DSM-IV mood and cognitive symptoms. That simplified definition did not include the somatic symptoms." He continues, "Our initial research found high levels of agreement in diagnosing MDD between the simplified and DSM-IV definitions of MDD. Our goal in this study was to replicate these findings in a large sample of psychiatric outpatients, and to extend the findings to other patient populations, including those presenting for treatment of pathological gambling and candidates for bariatric surgery."

Zimmerman says, "After eliminating the four somatic criteria from the DSM-IV definition of MDD, leaving the five mood and cognitive features, a high level of concordance was found between this simpler definition of MDD with the original classification in all three patient samples studied." He adds, "This new definition offers two advantages over the DSM-IV definition – it is briefer and therefore more likely to be recalled and correctly applied in clinical practice, and it is free of somatic symptoms, thereby making it easier to apply with medically ill patients."

Using the Structured Clinical Interview for DSM-IV (SCID), the researchers conducted a study of more than 2,500 patients. The patient population consisted of 1,100 psychiatric outpatients, 210 pathological gamblers who presented for treatment and 1,200 candidates for bariatric surgery. Across all patients, the level of agreement between the simplified definition and the DSM-IV definition was more than 95 percent.

The researchers note that there are implications to changing the criteria for MDD. Because their findings indicate that the simpler definition is highly concordant with the current version, there would be no meaningful impact on prevalence rates. Reducing the number of criteria, however, would reduce the time needed to fully assess criteria in patients and diagnostic interviews could be shortened.

Zimmerman and the researchers conclude, "In deciding how to proceed in the next version of the DSM, the conceptual and practical advantages of a briefer set of criteria that is easy to apply to all patients, particularly medically ill patients, needs to be weighted against the disadvantages of deviation from tradition."