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Classification and epidemiology 

Classification and epidemiology
Chapter:
Classification and epidemiology
Author(s):

Robert C. Baldwin

DOI:
10.1093/med/9780199671632.003.0002
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Key points

  • Current classificatory systems for depression underestimate the level of depression among older people.

  • In later life, the impact of having even just a few persistent symptoms of depression is considerable.

  • Poor health is strongly linked to depressive disorder in later life so that care homes and acute hospitals have an especially high prevalence.

  • Depressive disorder adds to the morbidity of many common medical disorders of later life.

  • In later life, be especially vigilant for organic causes of depression (systemic illness, cerebral disease, medication, alcohol).

2.1 Types of depression in later life

Depression can mean a symptom or a syndrome. As a symptom, the key to distinguishing morbid depression from the transitory low mood experienced by everyone from time to time is that, in depression, there is a qualitative change in mood. Those affected recognize this change in mood themselves. They may also be aware that the duration and frequency differ (most days, most of the time) from transient unhappiness and that even positive events produce little relief.

In recent years, there has been a significant change in how depression is conceptualized. Rather than fixed categories of depression into which the patient must be squeezed, the evidence suggests that depression is on a continuum, from normal sadness to pathologically severe depression (Paykel and Priest 1992). Nevertheless, in psychiatry, as in the rest of medicine, practice would be impossible without some kind of classification, and the most common approach is to set a threshold of symptoms above which a patient is said to have the syndrome of depression (see Box 2.1). The threshold is set by criteria agreed via one of the two international systems of classification, the International Classification of Diseases (ICD-10) (World Health Organization 1994) or the Diagnostic and Statistical Manual (DSM-V) (American Psychiatric Association 2013). Although broadly similar, the latter is easier to grasp and, according to evidence from treatment trials, more efficient in treatment decisions. The previous DSM classification (DSM-IV) is used by the English National Institute for Health and Care Excellence. The DSM-V scheme is outlined in Box 2.1 and specifies that five core symptoms must be present and one must be depressed mood or loss of interest or pleasure. These symptoms must be present for at least 2 weeks and are ‘pervasive’, that is they are there most days, most of the time, and they interfere with the way the person lives his or her life. The syndrome of major depressive episode is defined by criteria A–C.

Another way to look at the syndrome of depression is to look at its impact on the individual. Patients with the syndrome of mild depressive disorder are distressed by their symptoms but can continue to function in life relatively normally. In moderate depression, the individual is more subjectively distressed and can maintain function but with considerable difficulty. Those with severe depression are generally in marked distress and are often agitated or retarded. The ability to function in usual roles is severely limited.

Just because a patient does not meet the diagnostic threshold does not mean their symptoms are unimportant. Having a few symptoms persistently, especially if accompanied by impaired function or quality of life, is a key risk factor for major depression. Often termed sub-threshold depression or minor depression (or dysthymia if chronic), this low-level depression is not trivial since, among the older population, it is associated with adverse health effects, as discussed in the next section. Because sub-syndromal depression in later life is much more common than syndromal depression, its negative impact on the health of the older population is all the greater.

To summarize, depressive disorder is the overall term for any form of depression likely to require, or benefit from, intervention. The two main categories of depressive disorder are major depression and sub-threshold (sub-syndromal) depression. Table 2.1 incorporates some of the other terms that may be encountered and gives the relevant codes from the two major international classificatory systems discussed previously (Anderson et al. 2008). ICD-10 and DSM-V differ slightly in that, in ICD-10, only four symptoms are needed to make a diagnosis of depressive episode; this milder form of depression is included under sub-threshold depression.

Table 2.1 Classifying depressive disorder

Classification used in this book

DSM-V (code)

ICD-10 (code)

Major depression

Major depressive episode, single episode, or recurrent (296.21–296.36)

  • Depressive episode—severe (F32.2), moderate (F32.1), or mild with at least five symptoms (F32.0)

  • Recurrent depressive disorder—current episode severe (F33.2), moderate (F33.1), or mild with at least five symptoms (F33.0)

Sub-threshold depression (includes ‘minor’ depression)

  • Other unspecified depressive disorder (311) includes: recurrent brief depression, short-duration depressive episode; and depressive episode with insufficient symptoms

  • Adjustment disorder with depressed mood/mixed anxiety and depressed mood (309.0, 309.28)

  • Depressive episode—mild with four symptoms (F32.0)

  • Recurrent depressive disorder—current episode mild with four symptoms (F33.0)

  • Mixed anxiety and depressive disorder (F41.2)

  • Adjustment disorder—depressive reaction/mixed anxiety and depressive reaction (F43.2)

  • Other mood (affective) disorders (F38)

Persistent depressive disorder (dysthymia) (300.4)

Dysthymia (F34.1)

2.1.1 Differential diagnosis

The conditions to consider when interviewing a patient with significant depressive symptoms are shown in Box 2.2.

Depressive disorder is termed ‘organic’ if there is evidence of a direct link between the onset of depression and either a systemic or neurological condition or an ingested substance or drug. These are coded separately in ICD-10 (F06.31, F06.32) and DSM-V (293.83), although, clinically, they may be indistinguishable from major depression not linked to physical disorder or substance. Causes are discussed in more detail in Chapter 5. Depression accompanying dementia may be classified here, although DSM-V recommends coding both diagnoses if the mood component meets the criteria (see Box 2.1) for a full affective syndrome. Do not forget that alcohol can precipitate or prolong depression.

Bipolar disorder with an onset in later life is infrequent, but recurrent bipolar disorder (from earlier in adulthood) causing bouts of depression is not uncommon. This is known as ‘bipolar depression’.

Dysthymia (renamed persistent mood disorder in DSM-V) is a chronic depression with a duration of at least 2 years and a number of symptoms from Box 2.1, although less than that required for major depression. It is often difficult to separate this concept from depressive personality traits or, in older people, the depleting emotional effects of living with chronic handicapping illness. However, persistent mood disorder/dysthymia often has an onset in early life.

In mixed anxiety and depressive disorder, symptoms of depression and anxiety are both present but below the threshold for either depressive episode or generalized anxiety disorder. DSM-V introduces a specifier ‘anxious distress’. This may be especially relevant to older patients whose level of anxiety may mask the underlying depression. It comprises feeling tense, restless, worrying, poor concentration, anxious foreboding, and a feeling of impending loss of control.

Lastly, adjustment disorder with depressive reaction is diagnosed when depressive symptoms below the threshold for a diagnosis of depressive episode begin within a month of a serious threat or loss. Symptoms usually resolve within 6 months.

Psychosis can lead to depressive symptoms. Usually, it is clear that the patient’s major problem is the presence of delusions and/or hallucinations. By convention, in psychotic conditions, mild to moderate depressive symptoms are considered as secondary to the psychosis. A severely depressed patient may present with psychotic symptoms. If due to depression, psychotic experiences are usually ‘congruent’ that is mood is related to depressive themes of low self-esteem or hopelessness. Occasionally, this is not the case—psychotic symptoms are then termed ‘non-congruent’—in which case, the relative importance of the two sets of symptoms, depression and psychosis, must be weighed up. If depression is the more salient symptom, then psychotic depression can be diagnosed, as opposed to as primary psychotic disorder. The particular problem of hypochondriacal delusions is discussed in a later section.

2.2 Epidemiology

At all ages, the prevalence of sub-threshold depression significantly exceeds that of major depression. Early research (Kay et al. 1964) found that 10% of older adults in the community had what would now correspond to sub-threshold depression (that is significant symptoms but below the threshold for major depression), but only 1.3% met criteria for what we now call major depression. Remarkably similar figures were found in the much more recent EURO-DEP study of depression in later life, conducted in 14 countries—between 8.6 and 14.1% for depressive disorder overall and 1 to 4% for major depression (Copeland et al. 1999).

These rates of major depression are lower than those for younger adults. A low rate was also found in the influential North American Epidemiologic Catchment Area (ECA) study (Blazer 2003). Several explanations for the age-related differences in prevalence have been proposed. First, for reasons we do not know, the prevalence of major depression may fall with age. Second, the rates may be underestimates, because studies often exclude individuals in care homes where the prevalence of depression is high. Excluding people with depressive symptoms soon after bereavement from being diagnosed with depressive disorder is likely to disproportionately affect rates of diagnosis in older people. The strict checklist approach of DSM and ICD to diagnosing major depression may not be suited to older populations. There is some evidence for this. Prince et al. (1999) used an age-specific depression scale ‘EURO-D’ to compare symptoms of depression among older adults in Europe. Two factors encapsulated the majority of depressive symptoms. One was ‘affective suffering’ (characterized by depression, tearfulness, and a wish to die), and the other was a ‘motivation’ factor (comprising loss of interest, poor concentration, and lack of enjoyment). The motivation factor increased with age, whereas affective suffering remained the same across age groups. The constellation of symptoms suggested by the motivation factor does not fit readily with ICD or DSM. This factor may, therefore, be specific to later life, meaning that, rather than falling in later life, the prevalence of depressive disorder may increase when co-morbidity from depleting medical conditions is factored in.

Medical co-morbidity and cognitive impairment are the two key factors which affect the diagnosis and management of depressive disorder in older adults. Because of this, rates of depression (including major depression) in long-term care facilities, such as residential and nursing homes, are typically up to three times higher than among community residents (Blazer 2003). The combination of physical frailty and cognitive impairment results in even higher rates.

A similar picture is seen among older patients admitted to the medical and surgical wards of acute hospitals, with rates averaging 10–12% for major depression (Blazer 2003). Cognitive impairment is also associated with high rates of depression, upward of 17% for Alzheimer’s disease and even higher for vascular and subcortical dementias (Alexopoulos 2005).

Is age itself a risk factor for depression? In a large cohort study, Robert et al. (1997) found that healthy older people were not at greater risk of depression than younger ones. Higher prevalence with age was explained by the poorer health of the older subjects, rather than their age.

2.3 Impact of depression

In 1990, it was estimated that mental and neurological disorders accounted for 10% of the total disability adjusted life years (DALYs) lost due to all diseases and injuries. In 2000, this rose to 12%. By 2020, it is projected that the burden of these disorders, among all age groups, will have increased to 15% (World Health Organization 2001). Contained within this report, the Global Burden of Disease study (GBD 2000) indicated that unipolar depressive disorders accounted for 4.4% of the global disease burden, the fourth most disabling disorder after respiratory conditions, perinatal conditions, and HIV/AIDS and ahead of diarrhoeal diseases, ischaemic heart disease, and cerebrovascular disease.

Sub-threshold depression is associated with functional impairment approaching that of major depression (Blazer 2003). Risk factors for sub-threshold depression (minor depression) in later life are similar to those for major depression (see Chapter 5). Minor (sub-threshold) depression is also a risk factor for major depressive episode. Given the scale of sub-threshold depression, it alone adds substantially considerably to the burden due to depression.

Key references

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American Psychiatric Association (APA) (2013). Diagnostic and Statistical Manual Version V. American Psychiatric Association, Washington DC.Find this resource:

    Anderson IM, Ferrier IN, Baldwin R, et al.; on behalf of the Consensus Meeting; endorsed by the British Association for Psychopharmacology Evidence (2008). Evidence-based guidelines for treating depressive disorders with antidepressants: a revision of the 2000 British Association for Psychopharmacology guidelines. Journal of Psychopharmacology, 22, 343–96.Find this resource:

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      Prince MJ, Beekman ATF, Deeg DJH, et al. (1999). Depression symptoms in late life assessed using the EURO-D scale: effect of age, gender and marital status in 14 European centres. British Journal of Psychiatry, 174, 339–45.Find this resource:

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