The prevalence of psychiatric disorders in medical illnesses ranges from 16-60 per cent depending on the research methodology (selfreports or interviews; inclusion or exclusion of somatic items), the setting (out-patient or hospitalized), and the sample. In general, the frequency of psychiatric disorders in patients with heart disease⁽¹⁾ (coronary disease, heart failure), gastrointestinal diseases (irritable bowel syndrome), lung diseases (asthma, chronic bronchitis), and diabetes is 15-20 per cent. In patients with cancer and chronic pain it is 30-40 per cent; and in neurological diseases (Parkinson’s, multiple sclerosis, epilepsy) and dialysis it is 50 per cent. Ten to 20 per cent of patients have sub-threshold symptoms that nevertheless influence psychosocial functioning. The prevalence of psychiatric disorders among family members of people with chronic disabling conditions is only slightly lower. The most frequent are organic mental disorders (5-44 per cent), followed by substance abuse (10-25 per cent), anxiety disorders (10-30 per cent), mood disorders (9-13 per cent), personality disorders (6-9 per cent), somatoform disorders (5-9 per cent), mania and psychosis (1 per cent). Recognition by medical doctors is below 50 per cent and the referral rate to liaison services is approximately 1-3 per cent.

The most severe psychiatric disorders are frequently associated with social isolation, difficult relations with health-care providers, poor adherence to treatment, unhealthy lifestyle⁽²⁾ (nutrition, smoking, hygiene), side-effects of medication and substance dependence. The presence of psychiatric symptoms can also lead to failure to recognize physical symptoms. And yet some medical illnesses are more frequent in people with schizophrenia than in the general population.⁽³⁾ These conditions are cardiovascular risk (9.4 per cent in men, 7 per cent in women), diabetes (13 per cent), hypertension (27 per cent) and chronic conditions in general (41 per cent).⁽⁴⁾

Anxiety, fear, demoralization, a sense of loss, decreased pleasure, and thoughts of death are frequent in advanced debilitating physical disease even when there is no coexisting anxiety or depressive disorder.

Physical disease and its treatment may cause somatic symptoms similar to those of psychiatric disorders. And the ‘aetiological’ criterion of the DSM-IV-TR that requires exclusion of a physical cause is often difficult to apply in advanced medical illness, as are the criteria for depression. Endicott⁽⁵⁾ proposed replacing the four somatic items for depression (fatigue, insomnia, weight-loss, and difficulty in concentrating) with four psychological symptoms: depressed appearance, social withdrawal, brooding, non-reactive mood. However, this proposal risks excluding somatic symptoms which are a core manifestation of more severe forms of depressive disorder. In doubtful cases, an inclusive approach to somatic symptoms is preferable, and the risk of severe psychiatric disorders should not be underestimated.

Self-abasement and guilt are less frequent in medically ill patients. In assessing guilt, ethnic and cultural factors must be taken into account, for example, feelings of guilt are uncommon in depressed Arabs, whereas somatization is common.

Some syndromes in medically ill patients do not correspond to standard diagnostic categories but nevertheless influence functioning and the course of disease. The Diagnostic Criteria for Psychosomatic Research⁽⁶⁾ mention illness denial, thanatophobia, demoralization, and alexithymia. In medical illness, psychiatric disorders may manifest with somatic symptoms (see Chapter 5.2.3).

Table 5.5.2 gives some broad indications for the differential diagnosis of psychiatric disorders in the presence of medical illness.⁽⁷⁾

To be classed as a psychological reaction, the psychiatric disorder must develop at the same time as the onset of the medical illness or the treatment. In some conditions such as, pancreatic cancer, multiple sclerosis, the onset of psychiatric disorder may precede the recognition of the medical illness (e.g. Multidimensional evaluation of the care requirements is essential and codified approaches exist).⁽⁸⁾

Atypical symptoms occur in psychiatric disorders due to medical conditions. Drium is often complex with auditory hallucinations prevailing, whereas tactile, olfactory, and gustatory hallucinations are rare.

These are both psychological (see Chapter 5.6). and medical (see Chapter 5.3.4.

If properly treated, psychiatric disorders in medically ill patients have the same prognosis as those occurring without medical illness, except in some very advanced and debilitating cases, and in these, the few reported studies give contrasting results. Psychiatric disorders may significantly influence the outcome of the medical condition. Depression is associated with an increased risk for subsequent development of ischaemic heart disease, Parkinson’s disease, Alzheimer’s disease (and other dementias) and medical diseases in general. It is an independent predictor of severe complications in diabetes and of mortality in ischaemic heart disease, heart failure,⁽⁹⁾ stroke, dementia, cancer and HIV. Anxiety may exacerbate angina, arrhythmia, asthma, movement disorders, hypertension and irritable bowel syndrome and is associated with increased health-seeking behaviour and prescription of inappropriate drugs.

Delirium is reversible in 70-80 per cent of cases, but in terminally ill patients may be progressive and intractable, and is associated with increased short-term mortality.⁽¹⁰⁾ Mania and psychosis may worsen the medical outcome due to behavioural alterations, poor adherence and increased drug adverse effects.