Panic disorder and major depression. A tale of two syndromes.

Considerable research has been conducted to clarify relationships between panic disorder and major depression. From a number of perspectives, it now appears that panic disorder and major depression are not identical illnesses. While many patients with panic disorder are likely to experience an episode of major depression at some point during their lives, the timing of this occurrence is highly variable. While depression may be an expected and understandable result of having to live with chronic anxiety and phobic avoidance, the available evidence suggests that such a hypothesis is not particularly tenable. Depression can occur in individuals with or without severe agoraphobia and in individuals ill with panic for greater or lesser periods of time. Comorbidity in panic, particularly for social phobic or obsessive-compulsive symptomatology, does serve as a risk factor for the lifetime occurrence of depression and may denote a more severe illness. Biologic markers (Table 4), while of limited diagnostic utility in clinical practice, may reveal important pathophysiologic similarities and differences between panic disorder and major depression. Current evidence points to many areas of biologic overlap, with some important areas of independence (Fig. 7A). Although not extensively discussed in this chapter, several clinical parameters paint an analogous picture (Fig. 7B). There is a need for future studies of biologic markers in individuals over time, in various phases of illness. Furthermore, the study of multiple biologic markers in the same individuals would be a worthwhile pursuit, perhaps leading toward the delineation of underlying pathophysiologic mechanisms. In summary, then, we favor a conceptualization of panic disorder and major depression as nonidentical disorders with many shared characteristics. Future studies as suggested above, particularly when coupled with the power of genetic studies not described in this chapter, may eventually lead to a clearer demarcation of the boundaries between these two intriguing psychiatric syndromes.