Differential diagnosis and comorbidity

Depressive illness should only be diagnosed when the signs and symptoms lead to significant personal suffering and are accompanied by observable social impairment, although in mild depressions social impairment may be less obvious to the observer. The diagnosis requires clinical skills and time to elicit. Depressed young people will not describe their symptoms readily or easily, even to their parents. Although adolescents can be moody and unpredictable these do not constitute clinical characteristics of depression. Similarly tearfulness is of itself not a clinical characteristic of depression, particularly in younger children.

In specialist services and community studies depression seldom occurs as a single

psychiatric disorder (Mitchell et al., 1988; Goodyer & Cooper, 1993; Herbert et al., 1996). Concurrent symptoms of anxiety and behavioural disturbances are present in almost all cases, and between 50 and 80% of depressed cases will also meet criteria for another non-depressive disorder. Conduct disorder and/or oppositional disorder occur in around 25% of young people with depression, with a similar proportion meeting criteria for separation anxiety disorder. Around 15% will meet criteria for obsessive-compulsive disorder, and a further 5% will be concurrently suffering from an eating disorder,

other anxiety states or ADHD. Although the precise association between obesity and depression in children and young people remains to be clarified, it is likely that there is at least some degree of comorbidity. There is no known association with being mildly overweight and depression.

Although there is, as yet, no systematic evidence for an association between concurrent substance misuse and depression in young people, it is widely believed that many young people with depression turn to drugs in an attempt to alleviate persistent low mood. However, there is evidence to suggest that smoking in teenage boys is associated with an increased risk of comorbid substance misuse and psychopathology (including depression) in general (Boys et al., 2003; Meltzer et al., 2003a).

It is clear that depression in children and young people usually occurs in the context of other detectable problems or comorbidity. However, clinically it is important to avoid counting the same symptoms more than once. Thus, a double diagnosis should only be made when the signs and symptoms indicate the presence of two quite clear and separate psychiatric disorders, occurring at the same time. Very few cases have more than two comorbid diagnoses, and when they do occur they usually indicate severe psychiatric disorder.

3.3.1.1 Dysthymia

Dysthymia has been described as a chronic mood disturbance of young people

characterised by: long-standing gloom and dysphoria, brooding about feeling unloved and affective dysregulation. The dominant negative cognition is self-deprecation or negative self-esteem. There are high rates of irritability and anger in everyday circumstances, occurring as a hyperemotional response to social problems in the

everyday environment (Kovacs et al., 1994). According to DSM-IV, dysthymia is a chronic depressive condition that in childhood or adolescence presents with the same general characteristic of lowered mood (dysphoria or irritability) as depression, but of

insufficient severity to gain the full diagnosis. The symptoms must have been present for at least 1 year or more. ICD-10 requires that symptoms be present for 2 years or more and defines the disorder as likely to begin in late teens or early adult life and makes no reference to a childhood onset form. In addition to depressed mood the subject must have two out of a further six symptoms from the symptoms list for unipolar depression, except that feelings of guilt and suicidal behaviour are not included. The implication is that the latter two symptoms are not found in dysthymic disorders and if present suggest that the patient is likely to be suffering from an episode of depression. The best clinical description of dysthymia comes from the work of Kovacs and colleagues based on children referred to mental health services in Pittsburgh, USA. Compared with depression, dysthymia is distinguished by the virtual absence and significantly lower prevalence of anhedonia and social withdrawal; and comparatively lower levels of guilt, morbid preoccupation and impaired concentration. Practically none of the dysthymic children had reduced appetite and few had hyposomnia or fatigue (Kovacs et al., 1994).

In diagnosing dysthymia, it is important to establish that the patient does not fulfil criteria for current depression. If depression has preceded the onset of dysthymia then there must have been full remission of all depressive symptoms for at least 2 months before the development of dysthymia. By contrast, episodes of depression can be superimposed on dysthymia, in which circumstances both diagnoses can be given.

In the absence of a published evidence base for the treatment of dysthymia at present, in this guideline the treatment of dysthymia, if clinically necessary, should follow that for mild depression.

3.4 Aetiology

More than 95% of major depressive episodes in young people arise in children and young people with long-standing psychosocial difficulties, such as family or marital disharmony, divorce and separation, domestic violence, physical and sexual abuse, school difficulties, including bullying, exam failure, social isolation. A very small number of depressive episodes in children and young people will arise in the absence of prior difficulties, and resulting from an acute, very negative life event, usually involving a severe personal assault. Between 50 and 70% of cases are acute, occurring within a few weeks of a precipitating event, such as a breakdown in a personal confiding relationship. In the other 30 to 50%, onsets emerge more slowly against a background of family disharmony and/or friendship problems (Rueter et al., 1999; Goodyer et al., 2000a). There are multiple pathways to the onset of depression in adults and there is every reason to believe that the same is true for depressions across the lifespan (Kendler et al., 2002). Moreover, there are numerous aetiological theories to account for depression, including genetic, biochemical and endocrine, psychological, social and socioeconomic. None has gained widespread acceptance, although a pragmatic model, integrating the various theories (the ‘Stress-Vulnerability’ model; Nuechterlein & Dawson, 1984) has broad clinical utility and is widely subscribed to. In this approach, young people (or adults) will, to varying degrees, have a vulnerability to depression rooted in genetic, endocrine and early family factors, for example emotional deprivation or physical abuse. This vulnerability will interact with current social circumstances, such as poverty, social adversity or family discord, with stressful life events acting as the trigger for an episode of depression (Harris, 2000).

Although this model can be used to understand and research depression in children and young people, what counts as a current social factor in the young child may well count as a vulnerability factor for an adolescent. For example, about 30% of the variation in risk for adolescent depressive symptoms is genetic. Genes appear to act through increasing the liability for other ‘depressogenic’ risks, such as negative temperament, experiencing more negative life events and difficulties, or responding to them with more distress and impairment (Caspi et al., 2003b; Kendler et al., 2004). On the other hand, genetic factors overall appear somewhat less important in depressive symptoms arising in pre-pubertal children (Rice et al., 2002). Whether this is precisely the same for depressive syndromes and for a depressive illness in particular is not clear.

Biochemical theories of depression, such as the monoamine hypothesis, site at least some of the vulnerability to depression within the ‘serotonin systems’ in the brain (Birmaher & Heydl, 2001). Other monoamines have also been invoked. There is also evidence for a steroid vulnerability to depression (Birmaher & Heydl, 2001). This suggests that high cortisol levels precede the onset of depression and impair brain functions, including those of serotonin (Goodyer et al., 2000a). Of particular interest here, it appears that, amongst well adolescents, those whose mothers suffered with postnatal depression had higher circulating levels of cortisol (Halligan et al., 2004), raising the possibility that early events have long-term biochemical effects that may increase a young person’s vulnerability to depression.

Psychological processes, such as ingrained patterns of thinking, may also increase a young person’s vulnerability to depression. For example, the tendency to negative thinking about oneself at times of low mood, and the characteristic of ruminating or perseverating on these negative thoughts, in the presence of psychosocial adversity, are known to increase the risk for a depressive episode (Lyubomirsky & Nolen-Hoeksema, 1995; Kelvin et al., 1999; Park et al., 2004). Individuals who possess both these

cognitive characteristics appear to be particularly vulnerable to becoming depressed (Nolen-Hoeksema, 2000; Spasojevic & Alloy, 2001).

To reiterate, current social difficulties associated with depression in children and young people include marital disharmony, parental depression and other psychiatric disorders, family discord and maltreatment, including physical, sexual and emotional abuse. The most important non-familial factors are breakdown in friendships and substance misuse. Of course, once a child or young person is depressed, these same factors can act to maintain the state of depression. In addition, poor friendships and further negative life events during the course of the disorder are especially associated with longer duration of disorder (Goodyer et al., 2001). Although it is unclear as to why about 30% of first depressive episodes in young people persist beyond 18 months (Goodyer et al., 2003), strong ‘candidate-factors’ include chronic friendship difficulties, ongoing family discord and untreated severe symptoms.

In conclusion, acute life events associated with onset of a depressive episode are

personal disappointments derived in the main from friendship difficulties in adolescents and family discord in childhood. However, almost any event that carries a high

negative and distressing impact has the potential to trigger the onset of depression in vulnerable young people, with pre-existing chronic family (and/or friendship) difficulties (Goodyer, 2001).