Depression cannot be diagnosed unless it is first considered a possibility, neither will it be appropriately treated unless it is considered pathological. Depression may be missed when too much emphasis is placed on the presenting complaints of, for example, lethargy, anorexia or pain¹³. Depression and feelings of worthlessness may cause failure to complain of symptoms of physical illness or to ask for help. It may cause non-compliance with medication and other treatments, self-neglect or non-attendance at clinics. Alternatively, the lowering of self-esteem and decreased ability to cope can lead to increased attendance at clinics.

The lack of a concise definition for depression in the elderly makes the establishment of validity a difficult task, which can only be examined by longitudinal follow-up of patients to see what happens to their symptoms¹⁴. Somatic symptoms, such as lack of energy, poor concentration and weight loss, may be caused by the physical illness or ageing, not depression; even experienced clinicians may have difficulty attributing such symptoms to physical or psychiatric causes. Even feelings of life not being worth living and wishing to die are not always associated with depressed mood; poor subjective health, disability, pain, sensory impairment and living in an institution have been shown to be associated factors in the absence of depressive illness¹⁵.

The elderly tend not to admit to feelings of depression and relatives may be unaware of the condition¹⁶. Somatization, ‘the tendency to experience and communicate somatic distress and somatic symptoms unaccounted for by relevant pathological findings, to attribute them to physical illness and to seek medical help for them’¹⁷, is increasingly recognized. Somatization can still occur in those with genuine physical illness. The somatic symptoms of depression are similar to those of a chronic illness, such as cancer, and it must be remembered that depression and physical illness often co-exist¹⁸.

Hypochondriasis is a recognized symptom of depression in the elderly population¹⁹. However, in this age group, rigorous steps must be undertaken to exclude physical problems before ascribing symptoms to hypochondriasis or somatization^18,20. That such patients are depressed is inferred from their good response to standard treatments for depression²¹.

The 1991 National Institutes for Health (NIH) Consensus Statement on diagnosis and treatment of depression in late life concluded: ‘What makes depression in the elderly so insidious is that neither the victim nor the health provider may recognize its symptoms in the context of the multiple physical problems of many elderly people.’ DSM-IV allows somatic symptoms to be counted towards the diagnosis of depression if there is any possibility of psychological aetiology, a more inclusive and accurate means of diagnosis than previously.

Psychiatric morbidity in hospitals is higher than in the general population. Surveys of wards and clinics do not completely establish an association between psychiatric and physical morbidity because they may be biased for selective referral patterns: psychological symptoms can lead to help-seeking behaviour for physical illness in an individual who had previously been able to tolerate his or her physical problems. Similarly, they may influence a GP on whether or not to refer to hospital. Stress may be as important in triggering help-seeking behaviour as in triggering actual illness. In addition to the degree of distress, many other factors determine whether or not an individual will seek help, including religious and social values, socioeconomic background and personality.

Affective disorder in the elderly is strongly associated with physical ill-health²⁰: ‘whether or not such an illness has a direct aetiologi- cal relationship to the affective disorder, its practical importance must be considered, for it is bound to influence the course and outcome of the psychiatric condition.’ Although overall medical burden appears comparable in elderly patients with bipolar and those with major depressive disorder, patients with bipolar disorder have higher body mass index and greater burden of endocrine/metabolic and respiratory disease²².

Other studies have found that depression leads to increased mortality^23-25 over and above age effects, the prognosis worsening with severity of depression. Chronic illness, physical function and cognitive function all independently predict depressive morbidity in late life. The significance of depressive symptoms was demonstrated by their independent association with all-cause mortality at two-year follow-up²⁶.

Depression in the elderly may be due partly to a biological ageing process, which would directly increase mortality and morbidity²¹‘²⁷. Burvill and Hall²⁸ showed increased mortality in depressed elderly patients (n = 103, aged 60+) followed for five years if they were aged 75+, had impaired mobility or showed poor recovery with residual symptoms or chronicity. There were two peaks of increased mortality, one early in the disease and one late. Cardiovascular or pulmonary disease and malignancies were the predominant causes of death. The results are similar to those of the four-year follow- up by Murphy etal.²⁹, who also postulate that increased mortality seen in the depressed elderly (especially the men) was not caused by differences in physical health alone. They suggest:

• inadequate treatment of the depression, leading to cardiovascular complications from the antidepressant but no benefit to the patient; the depression itself can also provoke cardiac death, especially in men;
  
• ‘sub-intentional suicide’ in those who ‘turn their faces to the wall’;
  
• residual depressive invalidism, causing poor nutrition and decreased mobility; with attendant complications of susceptibility to infection, fractures, bedsores, etc., all contributing to the increased mortality.

Mortality in hospital was found to be significantly higher in those depressed but over 30% of those discharged had died within, on average, five months, whether depressed or not³⁰. The authors also noted that survivors with depression consumed more health care resources than did the non-depressed survivors. Among the depressed elderly, 40% have chronic poor physical health³¹; they use and need more medical services^32,33 than the non-depressed, but also use fewer social and recreational services³². An association has been found between poor mental health and subsequent physical disease, suggesting that positive mental health may significantly retard the decline in physical health with increasing age³⁴.

Physical illness affects the capacity for independent living, resulting in altered relationships with others, lowered self-esteem and vulnerability to depression. Serious illness may be seen by some as an unpleasant reminder of mortality, bringing apprehension and fear. Continuing physical illness is a poor prognostic factor for depression, although whether this is a result of a biological relationship or the psychological strain of being ill is uncertain.

Mortality in acute medical inpatients is significantly higher in those with associated depression, although the direction of causality is not established. For example, Silverstone³⁵ followed consecutive admissions for myocardial infarction, subarachnoid haemorrhage, pulmonary embolus or upper gastrointestinal haemorrhage for 28 days post admission; 34% were depressed and 47% of these had life-threatening complications or died, compared with 10% of those not depressed.

Mood disturbance can result from structural brain disease, alterations in neurotransmitter concentration or activity caused by drugs or biochemical disturbance. These affective symptoms may present during a physical illness or be the initial symptom of an otherwise occult physical disorder. Depression may be:

• the result of an illness, especially a painful or disabling one;
  
• iatrogenic (e.g. the result of steroid treatment);
  
• a symptom of the physical illness (e.g. hypothyroidism);
  
• an aetiological factor (e.g. alcohol abuse secondary to depression);
  
• a depressed patient adopting the sick role as a coping mechanism;
  
• a common aetiological factor, such as bereavement, causing both depression and physical illness; or
  
• coincidental.

The elderly are particularly susceptible to the side effects of drug treatment³⁶, especially as they are often subject to polypharmacy^37,38. Patients with drug-induced depression often have a past or family history of depression and the drug may have precipitated the disease by affecting the levels of available neurotransmitters³⁷. Depression can often be alleviated by cessation of the drug, although some patients will also require antidepressant treatment. The combination of a susceptible patient and a depressogenic drug may precipitate a depression sufficiently severe to lead to suicide³⁷.

Subjective rating of general health has been shown to be independently associated with depression in the elderly, including the very old^39-41. This can lead to presentation at primary care or emergency facilities, unnecessary investigations and risk of iatrogenic disease, and lower quality of life. Recognition and treatment of the depression may lead to improvement in the patient’s subjective perception of his or her health.

Physically ill depressed patients are more likely to be admitted to hospital than those who are not depressed⁴². Depressed patients have higher use of all categories of medical care, including admissions, laboratory tests and emergency department visits³³.

The presence of significant psychiatric disorder has been shown to adversely affect the course of medical admission^43,44, affective disorders in particular prolonging length of stay^{45 -47} (although the study by Ramsay et al.⁴⁸ did not confirm this) and increasing the

likelihood of admission to residential care⁴⁹. Psychiatric intervention has been shown to increase recovery rate, reduce duration of stay, reduce the need for residential care after discharge and therefore reduce costs^50,51. Importantly a diagnosis of major depression in older medical inpatients is independently associated with poor mental health in their informal caregivers six months later⁵².

Lipowski⁵³ has proposed that the subjective significance of an illness and its treatment (e.g. amputation, cancer), combined with the patient’s personality and social circumstances, is the key to the psychological response. The variety of physical illnesses found with depression would support this view. Depression may be a reaction to physical problems; it occurs more frequently in those with increasing numbers of medical diagnoses and may be precipitated by developing new physical illnesses^23,54. All illnesses except the very trivial involve an element of psychological adjustment. Serious medical illness is likely to be a potent psychological stressor, affecting body image, self-esteem, the sense of identity and the capacity to work and to maintain social, family and marital relationships⁵⁵. However, the majority of people adapt their lives to the demands of their illness, maximizing their prospects of recovery and return to previous levels of activity.

In the elderly, physical illness is frequently chronic and may worsen with time. This, combined with the losses suffered by many elderly people, such as loss of status and income on retirement, loss of friends and family by death and the fear of loss of independence and dignity due to the illness itself, can lead to the adjustment disorder merging imperceptibly into a depressive illness. This can be considered secondary depression⁵⁶, the depression following or paralleling a life-threatening or incapacitating medical illness. However, the prevalence of this type of depression is unknown, as it is difficult to differentiate from depression related to other stressors and previous history. Patients with this type of depression tend to have fewer suicidal thoughts but have more feelings of helplessness, pessimism and anxiety⁵⁷.

This is more common than medical illness presenting as depression, especially in the current generation of elderly, who tend to som- atize their psychological symptoms, having been brought up in a society which did not encourage the expression of emotion. Somatic symptoms in the elderly may represent physical illness, depression or emotional responses to physical illness. The somatic symptoms will need investigation, but depression, if suspected, should be treated.