by Janice L. Krupnick, Ph.D.
Professor of Psychiatry
Georgetown University School of Medicine
An important consideration in understanding posttraumatic stress disorder (PTSD) is its frequent co-occurrence with other psychiatric disorders. Population-based surveys of individuals who have been diagnosed with PTSD show that these persons have rates of 62% to 92% of other types of psychological disorders. In a major study of veterans who had served in Viet Nam (Kulka et al.1990), 99% suffered from another psychiatric disorder. While disorders such as panic disorder, other anxiety disorders, and substance abuse and dependence frequently co-occur with PTSD, the disorder that most commonly co-occurs is major depressive disorder. In the National Comorbidity Survey (Kessler, Sonnega, Bromet, Hughes, & Nelson, 1995), a major study investigating the prevalence of different types of psychiatric disorder in the United States, major depressive disorder was found to co-occur with PTSD in almost one-half of cases. Among men with PTSD, 47.9% had co-occurring major depression; among women 48.5% of those with PTSD also suffered from major depression.
Some observers suggest that it is not surprising that so many people who are diagnosed with PTSD also meet criteria for a diagnosis of major depression because many of the symptoms for both disorders overlap. For example, a number of symptoms of PTSD, such as diminished interest in previously enjoyed activities, problems with sleep, restricted range of emotions, and difficulty with concentration, are the same symptoms that commonly occur in depression. Some researchers have even suggested that one dimension of PTSD might be called a depressive cluster.
Until recent years, the role played by trauma exposure has not been central in the study of major depressive disorder. A number of studies, e.g., Burnam et al. (1988), Cascardi, O’Leary, & Schlee (1999), however, have shown that exposure to trauma is a risk factor not only for PTSD but also for major depression. One study of depressed elderly patients that included a short screen for PTSD found that 42% of these depressed patients also had PTSD. In a two-site study of depression treatments, DeRubeis and colleagues (2005) found that 17% of their study participants also had PTSD.