What is meant by 'mild' depression?

'Mild depression' is an inexact term, which may include mild episodes of major depression, less severe episodes that do not meet criteria for major depression, and dysthymia, which is a chronic depressive disorder.

International research definitions

The American Psychiatric Association defines a major depressive episode by the presence of at least five of the following symptoms (when not due to normal bereavement, physical illness, alcohol or drugs):6

? abnormal depressed mood

? abnormal loss of interest and pleasure

? appetite or weight disturbance

? sleep disturbance

? disturbance in activity (agitation or slowing)

? abnormal fatigue or loss of energy

? abnormal self-reproach or inappropriate guilt

? poor concentration or indecisiveness

? morbid thoughts of death or suicide.

At least one symptom must be abnormal depressed mood or loss of interest and pleasure, persisting for most of nearly every day for at least 2 weeks and significantly impairing function and daily life.6 A major depressive episode is classed as mild when the symptoms only just fulfil these threshold criteria and the patient has minimal functional impairment. When fewer than five depressive symptoms are present, the disorder is sometimes called minor depression. Dysthymia is defined by the presence of at least three symptoms, including depressed mood, on more days than not for at least 2 years.6

The World Health Organization defines depression similarly.7 According to its classification, diagnosis of a mild depressive episode requires the presence of at least four, but no more than five, symptoms, of which two must be depressed mood, loss of interest in normal activities, or decreased energy.

'Mild depression' in clinical trials

Most clinical trials in depression have specified that participants should fulfil research diagnostic criteria for major depressive disorder. Additionally, the depression is commonly ranked as 'mild', 'moderate' or 'severe' according to symptom scores, using validated instruments such as the 17-item Hamilton Depression Rating Scale (HDRS) or the Beck Depression Inventory (BDI). It is changes in these scores that are often used to assess the response to treatment. In general, a score of 14-20 (out of a maximum 67) on the HDRS, or 14-19 (out of 63) on the BDI, is considered consistent with a major depressive episode of mild severity.

What do GPs understand by 'mild depression'?

None of these definitions or scores is used routinely in primary care. Studies suggest that most depression that GPs treat is below, or only just reaches, the minimum diagnostic criteria for major depression.3^,4^,8 This implies that in many of the patients that GPs treat for depression the illness is mild. However, qualitative research suggests that GPs do not necessarily conceptualise depression just in terms of episodes of mild or severe psychiatric illness.9 Rather, GPs and their patients may see depressive symptoms much more in terms of fluctuating mood disturbances occurring in response to life situations, often against a background of chronic difficulties, physical illness, insecure relationships and deprivation.9 Treatment with an antidepressant seems sometimes to be given 'palliatively' in an attempt to ameliorate troubling symptoms, rather than to induce remission of an illness, and may be seen as subsidiary to supportive care given by the primary care team.

Prevalence and outcomes

UK studies conducted in the 1980s showed that around 5% of all patients consulting their GP met criteria for major depression, and a further 10% had milder depressive states, often accompanied by anxiety.10^,11 In a more recent study in the USA, the prevalence of all depressive disorders among patients attending their primary care physician was 23%, and of current major depression 13.5% (classed as 'mild' in 44%).12 Although mild depression may be a short-term reaction to adverse life events, it can cause significant impairment of functioning.13 Because it is more common than major depression, it probably results in loss of more working days.14

Relatively little is known of the natural or treated history of mild depressive disorders managed mainly or entirely in primary care. In prospective studies involving patients typical of those seen in UK general practice, around one-third to one-half recovered within 6 months with 'usual care', but 12-25% experienced unremitting symptoms over the course of 1 year.15^,16 'Usual care' here means any therapeutic intervention, referral or follow-up that the GP considered appropriate for the individual. Long-term follow-up studies (lasting 10-11 years) found that 50-60% of patients had at most a single recurrence of depression,17^,18 but up to 30% experienced relapsing and remitting symptoms, and around 18% had chronic symptoms.17 A poorer outcome was more likely in those who lacked social support or had a physical illness.15^,16

GPs do not detect depression in around one-half of patients at initial presentation,10^,19^,20 with detection being particularly difficult in patients who present with somatic complaints, or who ascribe their symptoms to physical or non-medical causes.21 However, GPs seem least likely to miss severe episodes of major depression,8^,19^,20 and much of what is missed is at the milder end of the spectrum and appears more likely to improve spontaneously.7^,8^,20 Also, depression that is missed initially is often diagnosed at subsequent consultations.19 This suggests that, often, a missed diagnosis is not necessarily of serious clinical consequence, although, in a prospective study in UK general practice, 14% of those initially missed remained undiagnosed and significantly depressed 3 years later.22

Use of simple screening questionnaires has been advocated to increase recognition of patients with depression in primary care,17^,23 and systematic reviews have found that feedback of high-scoring results increases the detection rate but does not effect the rate of intervention or the clinical outcome.24^,25 There is no evidence that routine screening with feedback of all results to the GP improves detection.24^,25

Antidepressant drug therapy

Antidepressant prescriptions issued by GPs in the UK more than doubled between 1975 and 1998, to 23.4 million per year, mainly due to increased prescribing of selective serotonin re-uptake inhibitors (SSRIs).26 Possible reasons for the rise include greater awareness of depression; wider adherence to guideline advice to continue with a full antidepressant dose for at least 4-6 months after resolution of symptoms; new (wider) indications for antidepressant therapy; and promotion of new drugs by industry. Also, the availability of SSRIs may have made it easier to initiate treatment, because they generally require less dose titration than tricyclic antidepressants (TCAs). It is probable, however, that much antidepressant prescribing in primary care is for patients with mild depression, in whom the evidence for efficacy is weak.1^,5^,27

Clinical evidence

Of the few randomised controlled trials investigating antidepressant drug treatment in primary care, nearly all have enrolled patients who met research criteria for major depressive disorder of at least mild to moderate severity. A few small double-blind placebo-controlled studies, conducted in UK general practice and lasting 12-24 weeks, have shown significant benefit from TCAs and SSRIs in such patients.28^,29 Also, an 8-month randomised study conducted in primary care in the USA, showed that, in patients with major depression, treatment with nortriptyline (supported by energetic measures to encourage patients to take a full therapeutic dose) was more effective than usual care.30 However, these studies shed no light on whether antidepressant therapy helps patients with depressive symptoms below, or barely above, the threshold for major depression. One randomised double-blind placebo-controlled study, conducted 15 years ago in UK general practice, and lasting only 6 weeks, showed benefit from amitriptyline in patients meeting research criteria for "probable or definite major, minor or intermittent depression".31 A post-hoc subgroup analysis, limited to 141 patients who completed at least 4 weeks' treatment, suggested that this benefit was significant in those with a baseline score on the HDRS as low as 13, but not in patients with milder depression (HDRS 6-12).32

Evidence of benefit in dysthymia is more convincing but comes almost entirely from short-term (up to 12 weeks) randomised studies in hospital outpatients. A meta-analysis of 15 such studies, involving a total of 1,964 patients with dysthymia and other non-major depression of at least 2 years' duration, showed significant improvement with TCAs (number needed to treat [NNT] 4.3, 95% CI 3.2-6.5) and with SSRIs (NNT 4.7, 95% CI 3.5-6.9) when compared with placebo.33 Most studies had significant methodological weaknesses, and caution is needed in extrapolating the findings to longer-term treatment of patients with dysthymia in primary care.

In a study in the USA, adult primary care patients with dysthymia or minor depression (241 patients aged under 60 years34 and 415 patients aged 60 years or over35) were randomised to antidepressant therapy (with paroxetine), problem-solving therapy (six sessions) or placebo drug therapy. By 11 weeks, the score for depressive symptoms (the main outcome measure) had improved by a similar amount with all three treatments in patients under 60 years; however, the score improved more with paroxetine than with placebo in older patients.34^,35 In those under 60 years with dysthymia, paroxetine appeared more effective at bringing about remission than did either placebo (remisson rate 80% vs. 44%, p=0.008) or problem-solving therapy (57%) - but the analysis was applied only to the subset of patients who received "adequate treatment exposure" as defined in the protocol. In older patients with dysthymia and patients with minor depression, remission rates did not differ between the treatment groups.

Psychological treatments

Surveys suggest that many people view depression as a reaction to life difficulties, and consider counselling preferable to treatment with antidepressants.36^,37 Also, in general practice-based trials that allowed participants to express a preference, most patients chose counselling or cognitive behavioural therapy rather than usual GP care38 or antidepressant therapy.39

Counselling

Counsellors come from many different professional backgrounds and use different approaches to treatment. Usually, however, the key element in counselling is reflective listening (avoiding direct advice) to enable patients, over a series of sessions (typically six), to think about and try to resolve their own difficulties. In primary care in the UK, accreditation with the British Association for Counselling and Psychotherapy (BACP) is widely accepted as a standard for practice.40

Clinical evidence

A meta-analysis of six randomised controlled trials, conducted in UK general practice and involving a total of 741 patients with various emotional and behavioural problems, found that counselling by a BACP-accredited counsellor was more effective than usual GP care in reducing symptoms of depression and anxiety in the short term (1-6 months).40 Overall, approximately 36% of patients in the counselling group had clinically significant improvement by 4 months, compared with 23% in the usual-care group.40 However, counselling appeared no better than usual care in improving the symptoms in the long term (beyond 6 months), nor in improving social functioning. Even so, most patients were highly satisfied with, and felt helped by, counselling.40 It is not clear what proportion of patients in these studies can be characterised as having 'mild depression', and some studies included only patients with symptom scores consistent with moderately severe depression. Although economic data from the trials suggested that counselling might cost no more than usual GP care,40 a recent meta-analysis has shown that the studies lacked statistical power to provide reliable conclusions about the costs or cost-effectiveness of counselling in this setting.41

Specific psychological therapies

Several modalities of brief psychological therapy have been investigated for the treatment of depression. The main modalities studied in primary care are cognitive behavioural therapy, interpersonal therapy and problem-solving therapy. As with drug treatments, the great majority of trials have involved hospital outpatients with major depression.

Cognitive behavioural therapy (CBT) utilises cognitive techniques (e.g. to challenge 'automatic negative thoughts' and maladaptive beliefs) and structured approaches to modify dysfunctional patterns of behaviour. Patients are required to keep 'homework' diaries of symptoms, thoughts and behaviours. Treatment can involve up to 10-20 sessions with a trained therapist, so is a relatively expensive intervention.

Interpersonal therapy focuses on the relationship between current interpersonal experiences and depressed mood, and aims to reduce depressive symptoms by improving the quality of relationships and social functioning. Interpersonal therapy has mainly been studied in the USA, and is not widely available in the UK.

Problem-solving therapy aims to identify significant problems in the patient's life and to generate practical and achievable solutions for the patient to implement between sessions. Practice nurses can be trained to administer problem-solving therapy, but trained therapists are not widely available in primary care in the UK.

Clinical evidence

A systematic review identified 13 controlled trials (including a total of 886 patients) comparing brief psychological therapy with usual care or a waiting-list control group in patients with major depression.42 Six studies were conducted in primary care (four in the UK), of which five used CBT and one used interpersonal therapy. Compared with patients receiving usual care, those receiving brief psychotherapy were more likely to experience remission of depression (odds ratio 3.01, 95% CI 2.37-3.99). Benefit remained significant during follow-up for up to 9 months.42 No separate pooled analysis was conducted for the six primary care studies, and the authors cautioned against assuming the findings held for UK primary care. We are not aware of any primary care studies specifically designed to investigate CBT or interpersonal therapy in patients with minor depression or dysthymia.

Small randomised studies in UK general practice suggest that problem-solving therapy may be as effective as TCAs or SSRIs in patients with moderate depression.28^,43 However, another study found no advantage from problem-solving therapy compared with placebo drug therapy or usual GP care in 70 patients with a range of apparently milder depressive disorders (some very mild and recent, others longstanding).44 A study in primary care in the USA reported a short-term remission rate of 57% with problem-solving therapy in patients aged under 60 years with dysthymia, compared to 44% with placebo drug therapy, but no statistical analysis was presented.33 Problem-solving therapy gave no clear benefit in older patients with dysthymia or patients with minor depression.33^,34

Self-help psychological treatments

In the UK, the shortage of trained therapists means that access to most psychological treatments is limited. Where it is available, NHS waiting times for CBT are often over a year. Various forms of supported self-help therapy, usually structured around CBT principles, have been devised in an attempt to make the potential benefits of such therapy more widely accessible. 'Bibliotherapy' provides the patient with a treatment programme, presented as a booklet or a series of leaflets (sometimes with accompanying audiotapes). Interactive computer programmes, based on CBT, have also been developed. Such self-help tools can enable the patient to work through a treatment programme, more or less independently, supported by intermittent contact (e.g. by telephone) with a healthcare professional (which is important both to encourage continuance and to monitor for any deterioration).

Clinical evidence

Recent systematic reviews have concluded that bibliotherapy45 and computerised CBT programmes46 can provide modest benefit, additional to that from usual care, in patients with depression and/or anxiety. A subsequent randomised trial, involving 167 patients in general practices in the UK, found greater improvement in anxiety and depression, and in work and social adjustment, after a 9-week computerised CBT programme, supported by nurses, than with usual GP care.47 Benefit was independent of the duration, and baseline severity, of depressive symptoms or concomitant use of antidepressants, and was still present 6 months after the programme ended.47

St John's wort

Extracts of the plant Hypericum perforatum (St John's wort) are widely used as herbal remedies for depression. The pharmacologically active constituents have not been precisely identified. Hypericum is unlicensed as a medicine in the UK, but can be bought from pharmacies, supermarkets and health food shops.

No long-term efficacy and safety data are available on use of hypericum. A meta-analysis of 27 randomised controlled trials (eight in general practice), involving a total of 2,291 patients with mainly mild or moderate depression, found hypericum extract more effective than placebo (responder rates 56% vs. 25%; rate ratio 2.47, 95% CI 1.69-3.61; NNT 3.2), and as effective as, and better tolerated than, TCAs (given mainly in low doses).48 However, most of the studies had important methodological flaws,49 and none lasted longer than 6 weeks. Subsequent randomised placebo-controlled studies have yielded conflicting results. Hypericum gave benefit (matching that of imipramine) in an 8-week study in general practice patients with mild or moderate depression, present, on average, for less than 6 months.50 By contrast, it was no more effective than placebo in two large studies conducted in the USA in outpatients with similarly severe, but more longstanding, major depression.49^,51

Hypericum may lead to symptoms of serotonin excess including tremor, gastrointestinal upset, headache, and restlessness if taken with an SSRI, especially in older patients.52 It may also interact with other prescribed medication, for example, lowering plasma concentrations of warfarin, theophylline and oral contraceptives52 so it is important that prescribers ask patients whether they are taking it.

Conclusion

Mild depression is common and is managed almost entirely in primary care. In many patients, the depressive episode appears to resolve spontaneously within 6 months or a year, but in perhaps one-fifth of patients, symptoms persist and become chronic and disabling. Most patients in general practice with mild depression fall below the conventional thresholds of severity used in clinical trials. Consequently, there is a lack of reliable efficacy data for most forms of treatment.

In general, benefit from antidepressant drug therapy has not been convincingly demonstrated in primary care patients with recent onset of depressive symptoms that do not meet the criteria for major depressive disorder. Evidence, mainly from hospital studies, suggests that a trial of treatment with an antidepressant is indicated for people with dysthymia, a condition in which mild depressive symptoms have become chronic and persistent, but confirmatory studies in primary care are needed. Most depressed patients seen in general practice would prefer psychological treatments, of which counselling is currently the most widely available in the UK. Counselling, administered by a fully trained practitioner, may help relieve symptoms of depression and anxiety more quickly than routine care and provides a setting for patients to explore current emotional difficulties. Cognitive behavioural therapy (CBT) is the psychological treatment of choice in outpatients with mild to moderate major depression, but it has not been thoroughly investigated for mild depression in primary care. Supported self-help programmes, based on CBT, may help to make this form of psychological therapy more accessible.

For many patients with depressive symptoms seen in general practice, a supportive 'watchful waiting' approach is reasonable. An immediate prescription for antidepressant medication is not usually justified. However, GPs need to take a careful history to exclude a major depressive illness that may warrant more urgent intervention, and should ensure that patients with mild depression are followed up, in order to identify and treat those who deteriorate or whose symptoms show signs of becoming chronic. Listening to patients' understanding of their illness and what they think would help (including assistance with social needs, isolation and physical disability), should help to guide appropriate medical and non-medical interventions.