Differences Between Persistent and Nonpersistent Depression
A number of studies have identified meaningful differences between persistent and episodic forms of depression that suggest the importance of distinguishing between these conditions.3,42
Rates of comorbid anxiety, substance use, and personality disorders are consistently reported to be higher among persons with chronic depression than those with episodic depression in both clinical and community samples.26,27,37 For example, Pepper et al.37 found that 60% of patients with DD, compared to 18% of patients with nonchronic MDD, met criteria for a personality disorder and that this difference was corroborated by informants’ reports. Rates of borderline, avoidant, and dependent personality disorders are particularly elevated in the chronically depressed patients.7,42
The association with personality disorders suggests that persistent depression may also be linked to more fundamental abnormalities in personality or temperament. In their influential model, Watson and Clark43 proposed that depression is associated with high levels of negative emotionality (NE) and low levels of positive emotionality (PE). NE, which is analogous to neuroticism, reflects sensitivity to negative stimuli resulting in a range of negative moods, such as sadness, fear, anxiety, and anger. PE, which is closely related to extroversion, includes exuberance, reward sensitivity, and sociability. PE and NE may play particularly important roles in chronic depression. Thus, patients with dysthy- mia and double depression report higher levels of NE and lower levels of PE than do patients with nonchronic MDD and healthy controls.44-46 A problem in interpreting these data is that the depressed state influences assessments of personality. However, Hirschfeld47 found that even after recovery, individuals with a history of DD exhibited significantly greater NE and significantly lower PE than did individuals with a history of MDD and individuals with no history of psychopathology.
There is suggestive evidence that personality/temperament differences may be evident prior to the development of chronic depression. Using examiner’s ratings of the laboratory behavior of a large cohort of 3-year-olds, Caspi and colleagues48 identified a cluster of “inhibited” children who were characterized by a combination of low PE and high NE behaviors, including sluggishness, low approach, social reticence, and fearfulness. Children in this cluster had significantly higher levels of parent-rated internalizing behavior problems at ages 13 and 1549 and elevated rates of interview-assessed depressive disorders and suicide attempts (but not anxiety disorders, alcoholism, or antisocial behavior) at age 21.48 Although the investigators did not report whether the same children exhibited these problems at each time point, many of these youths may have had depressive symptoms that persisted from adolescence to young adulthood.