MUS are a source of great diagnostic confusion for GPs. This is not simply because, by definition, they are symptoms for which no pathophysiological cause is readily identifiable. It is also because of uncertain case definition and variable clinical context.

Uncertain case definition

There is disagreement between clinical authorities as to how MUS should best be understood (Box 5.1). Physicians see them as functional syndromes, related to their sphere of expertise: IBS for gastroenterologists, fibromyalgia for rheumatologists, non-cardiac chest pain for cardiologists, and so on. Many psychiatrists see them as somatisation disorders, manifestations of underlying mental disorders such as anxiety or depression, although they disagree among themselves about the precise ways in which somatisation disorders should be classified. Psychologists may focus on symptom amplification, referring to a patient’s tendency to attribute amplified or exaggerated symptoms such as pain or distress to a presenting problem such as osteoarthritis of the knee. Health service researchers focus on problems of frequent attendance in primary care, or excessive referrals to secondary care and the wasteful costs to the healthcare system which ensue. Other researchers, including me, focus on problems in communication between patients and health professionals.

Variable clinical context

The clinical context within which patients present with MUS can vary considerably (see Box 5.2). In primary care patients commonly present with several symptoms, each of which may have a different degree of medical explicability. MUS may occur in the context of confirmed disease, whether physical or psychiatric. Medical explicability may also vary over time. In about 10% of symptom presentations initially considered as unexplained, a pathophysiological diagnosis becomes apparent within the following 12 months. Conversely, symptoms that appear to be clearly attributable to a recognised disease process can persist even when tests indicate that the assumed disease process is not present.

Let us consider how this confusion affects our understanding of the problems presented by ‘Frank’, a 38-year-old plumber.

If Frank sees a gastroenterologist he is likely to receive a diagnosis of IBS. If he is interviewed by a psychiatrist, he might fit criteria for DSM-IV somatoform disorder. His symptoms are not fully explained by a general medical condition, the direct effect of drugs or another mental disorder; they cause him clinically significant distress, and lead to impairment of social, occupational and other areas of functioning. He does not fulfil criteria for full somatisation disorder: for this he would need to complain of at least 12 different symptoms over many years. However, he does meet criteria for abridged somatisation disorder, since he presents with at least four somatic symptoms. He may meet diagnostic criteria for an anxiety disorder, and possibly for major depression. A psychologist would focus on Frank’s symptom behaviours, particularly his fear that his pain is going to get worse.