The outcome of depressive disorders in the setting of neurological illness

• depression
• neurological illness
• outcome
• quality of life

The depressions are a heterogeneous group of conditions. This is particularly true when depressive symptoms are experienced in the setting of coarse brain disease. Here the clinical presentation, differential diagnosis, and aetiology offer unique challenges to the clinician. The development of broader, more patient centred outcome measures such as quality of life and “health gain” has also elevated the status of depression, particularly because depressive symptoms are now seen to be the primary contributors to morbidity in some neurological illnesses. Two recent studies showed how depressive symptoms accounted for much more of the variance in morbidity in Parkinson’s disease (40%) than did movement disorder (17%).^1,2 Critics of these studies could rightly point out that before the advent of L-dopa, motor disorder was definitely the biggest contributor to morbidity in Parkinson’s disease, and that quality of life as a measure is more directly related to mood state in its broadest sense. Nevertheless, a more neuropsychiatric model of brain disease has developed, where cognitive and affective symptoms are seen in the same light as motor or somatic symptoms.

There are several factors that affect outcome in depression in the setting of neurological illness. First there is a question of whether the depression is being recognised. Most studies of patients within neurological clinics suggest that is it not. The next question is whether or not treatments for depression are effective in the setting of neurological illness. The answer to this question depends on which neurological condition is in consideration. The plethora of small case series in different neurological disorders suggests that antidepressants and cognitive behaviour therapy are effective (as both are clearly proven to be in “idiopathic” depression) but there is a dearth of randomised controlled trials in this area. The most notable is the lack of treatment trials for depression in the setting of Parkinson’s disease. Finally, neurological illnesses greatly differ in their course, outcome, and tendency to produce disability, all of which could directly affect the course and prognosis of any co-morbid affective disorder. To use the example of multiple sclerosis, Chwastiak et al looked at depressive symptoms in a community sample of people with multiple sclerosis and found two groups who were more at risk of depression—those early in the course of illness and those with severe physical disability.³

The data from the study by Carson et al (see pp 893–896, this issue) show that depressive illness is common in neurological outpatients (40% with major depressive disorder) and that the incidence over the study period was also high (with 20 new cases, of a total of 226, arising during the study period of eight months).⁴ The majority of the people with depression initially were still depressed at the end of the study. Recovery from depression in the study period was associated strongly with “health gain” (measured by the SF-36), but this was independent of physical status, although the numbers were small. The study does not address the issue of whether depression was recognised or treated adequately during the study period, and this would be a suitable subject for further investigation.

In another study from the same centre (see pp 897–900, this issue),⁵ depression is related to the presence of medically unexplained neurological symptoms. An eight month prospective study of this group of patients showed an increased rate of depression and anxiety compared with patients with clear “organic” disorders at baseline. Physical recovery at eight months was accompanied by comparable improvement in mental health.

What lessons can be learned so far? Depression is a common and disabling feature in neurological outpatients, and neurological clinicians should give greater prominence to its diagnosis and management. Brain disorders should be seen from a more neuropsychiatric perspective, with cognition and affect considered on a par with motor and other somatic domains. These lessons add weight to the argument for more integrated training in brain disorders, with neurological trainees in particular having tuition in the recognition and treatment of abnormal mental states in the setting of neurological illness (possibly in exchange for training psychiatrists in neurological examination and diagnosis).

Treatment trials are definitely needed to assess the efficacy of pharmacotherapy and psychological treatments (particularly cognitive behavioural therapy, which has a place in the management of patients who are already on multiple drug treatment or who would find antidepressants difficult to tolerate).

Finally, further studies could continue to address depression in specific neurological disorders, looking at phenomenology, illness course, and treatment response. Studies of depression in a neurology clinic setting could be done as an audit of clinical practice, to ascertain whether or not clinicians were recognising and treating depression effectively.