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Depressive disorders have traditionally been perceived as acute, episodic conditions. Over the last 2 decades, however, it has been increasingly recognized that many patients experience a long-term, chronic course of depression. Naturalistic studies suggest that between 7% and 12% of depression patients who are prospectively followed up will experience a chronic course (1,2). Approximately 20% of naturalistically treated patients with acute major depressive disorder (MDD) will not recover in the first 2 years of their depressive episode (3), and some 12% of these will not recover within 5 years (1). Further, the incidence of chronicity appears to be high across a range of populations. Community studies indicate a point-prevalence rate for chronic depression of between 2% and 6% (4,5). Chronic depressive disorders are also common in psychiatric outpatient samples, where they are frequently comorbid with other conditions (6,7). Overall, it has been estimated that chronic depression accounts for 30% to 35% of all cases of depression (5,8). Depression in general (9) and chronic depression in particular (10,11) pose a major public health problem. Patients with chronic depression often have marked impairments in psychosocial and occupational functioning (11–13). This reduced functioning is in turn associated with poorer prognosis (10,14,15). Chronic depression is also associated with high rates of health care use (3,16,17) and more frequent suicide attempts and hospitalizations (18). Accurate detection of chronic depression is particularly important, given the disorder’s significant clinical and public health implications. Current evidence suggests, however, that identification rates for acute MDD are poor (19). Detection rates for chronic depression are likely to be even lower, owing to both patient and physician factors. Patients may adapt to chronic depression, and the condition may eventually be perceived as normal, entrenched, or inappropriate for treatment. Physicians may fail to recognize chronic depression because patients tend not to complain about their depressive symptoms, because it is masked by other comorbid disorders, or because it is seen as a part of the patient’s personality. Even if it is correctly identified, the current management of chronic depression appears to be far from optimal. Significant numbers of patients either receive no treatment at all or receive low-intensity treatment, such as subtherapeutic medication dosages (6,20,21). Unsuccessful treatment is likely to demoralize both the patient and the physician. The literature concerning the current detection and treatment of chronic depression makes for bleak reading. However, encouraging evidence has recently emerged to help dispel the pervading myths that chronic depression has a poor prognosis and is resistant to treatment. Chronic depressive disorders in fact appear to be eminently treatable, provided that the intervention is thorough and vigorous. This article provides a brief update on the diagnosis of chronic depression subtypes and a review of the current evidence base concerning their optimal treatment. It concludes with a section focusing on the translation of this evidence into everyday practice and on some key areas for future research. Diagnosis of Chronic DepressionThe recent literature has discussed 4 main diagnostic types of chronic depression:
MDD, currently in a chronic episode, describes those patients in whom a depressive episode, with full episode criteria, has persisted for at least 2 years. Onset of chronic MDD tends to occur in early to midlife and may continue indefinitely. In a large study of patients with chronic MDD or double depression, mean lifetime illness duration was found to be 17.2 and 15.6 years respectively (21). Thus, it is not unusual for many patients with chronic depression to experience depression for most of their adult lives and for depression to be perceived as part of their personality. Disconcertingly, 43% of the sample had never received antidepressant pharmacotherapy, and only 20% had received a prior adequate antidepressant trial. Dysthymic disorder is a lower-grade, chronic (that is, also persisting for more than 2 years) depressive disorder that is usually found in primary care populations. Whereas chronic MDD is characterized by consistently low mood, dysthymia is more sporadic and changeable in nature, tending to have an earlier onset and concomitantly longer periods of illness duration. Dysthymia also appears to be underrecognized and undertreated (6); it is associated with significant psychosocial impairment (9,12) and high health service use (4). Approximately 40% of patients with dysthymia have coexisting MDD (4) or the so-called “double depression” form of chronic depression. These patients frequently return to a dysthymic rather than euthymic state following recovery from their major depressive episode (MDE) (22). The final category of chronic depression includes patients with an MDE from which they have only partially recovered, with lack of complete remission persisting for at least 2 years. Several studies have now indicated that residual symptoms following MDD are associated with greatly increased risk of relapse (23,24). Such findings suggest that the goal of acute treatment for depression should be the complete remission of symptoms (25,26). In practice, however, the rigid classification and diagnosis of chronic depressive disorders may not prove to be particularly useful. There has been ongoing controversy, for example, concerning the distinction between pure dysthymia and double depression (22,27). Research has shown that up to 79% of dysthymic patients will eventually develop an MDE, thereby qualifying for the diagnosis of double depression (8). More importantly, several studies have shown no significant differences in response rates between patients with pure dysthymia and those with double depression, suggesting that such differentiation may not have significant treatment implications (21,28). Treatment of Chronic Depression: The Evidence BaseCurrent treatment of chronic depression appears to be far from optimal, despite growing evidence indicating that chronic depressions respond well to several psychiatric interventions. The following section provides an update on the evidence base for the treatment of chronic depression. We identified key studies in this field via a systematic electronic search of Medline (from January 1, 1966, to November 30, 2001) and the Cochrane Library, using the key words chronic, persistent, or long-term depression and treatment, and hand-searched specialist journals and article bibliographies. We included only randomized controlled trials (RCTs) and metaanalyses. Table 1 summarizes the key studies addressing the treatment of chronic depression, excluding pharmacologic studies of the treatment of dysthymia, which have been comprehensively reviewed elsewhere (29,30).
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