Depression

Comorbidity

Depression is often associated with anxiety and anxiety is a common symptom of depression. The relationship between these two disorders is still being established and will undoubtedly receive further attention in the future, but the overlap is significant. Nearly half of depressed patients have anxiety symptoms and half of anxiety patients have depressive symptoms.

Anxiety is not a requirement for the diagnosis of major depression, bipolar disorder or dysthymia, as presented in either DSM-IV (American Psychiatric Association, 1994) or ICD-10 (World Health Organisation, 1992), in which mood and anxiety disorders are recognised as separate and distinct diseases. However, the idea that they may lie on a continuum has never been completely abandoned and the concept is supported by the fact that a group of 'in-between' patients with symptoms of both anxiety and depression has repeatedly been described (Angst, 1997). There are indications that anxiety is one of the most prevalent symptoms in clinical depression and that both the assessment and treatment of severe anxiety are of vital importance in the successful treatment of depression.

A recent epidemiological study, carried out under the auspices of the World Health Organisation, of the association between anxiety and depression (Sartorius et al., 1996), confirmed the associations between the two disorders. The anxiety symptoms also seem to be more pronounced in the depressed elderly and in patients with concomitant medical disease. Another authority (Liebowitz, 1993) confirmed the co-occurrence of the two disorders and suggested that anxiety symptoms should be taken into account when assessing which antidepressant is most appropriate for an individual patient to optimise treatment outcome and speed of recovery.

Anxiety occurs frequently as a comorbid disorder with depression, with 42-72% of depressed patients reporting symptoms of worry, psychic anxiety and somatic anxiety of at least moderate severity (Fawcett and Kravitz, 1983); these depressed patients with higher anxiety levels experience significantly longer time to recovery, a higher rate of multiple drug treatments, a higher incidence of suicide, and more frequent episodes of depression. This pattern has been confirmed in other reviews (Joffe et al., 1993; Angst, 1997).

The increased severity of depressive illness associated with anxiety symptoms was also highlighted in a study by Coryell et al. (1988) in which the depressive symptoms of patients were reported to be significantly more severe in those reporting panic attacks than in those patients who did not report such attacks. In another study, there was a significant delay in the recovery time from major depression in patients with comorbid obsessions and compulsions (Coryell et al., 1992).

Angst et al. (1997) have called for the recognition of subthreshold categories of depression, anxiety, and mixed anxiety and depression, the incidence of such disorders being far higher than previously recognised. The results of the work by Angst and his colleagues (1997) revealed that nearly half of young adults in the community reported either anxiety or depression at least once in the 15 years of observation; when the two subthreshold categories co-occurred the episode seemed far more severe. These patients did not qualify for the diagnoses of either depression or anxiety disorders but they nevertheless suffered significant symptoms that were accompanied by a substantial degree of functional impairment.

Suicide rates are also influenced by comorbidity. In studies by Wålinder (2000) and Angst (1997) the suicide rates of depressed patients were found to be 5-7%, of panic disorder patients 4-7% and the suicide rates of patients suffering from both depression and panic disorder were 19% in the Wålinder study and 29% in the Angst study.

Mood and anxiety disorders frequently overlap, and the extent of this overlap is now being recognised more clearly. This can be attributed to the efficacy of the SSRIs in the treatment of both the mood and the anxiety disorders. It is important that we recognise the impact that anxiety symptoms may have on treatment duration and outcome in depressed patients.