F E AT URE C L INI C AL RISK RED U C T I O N
UDIAGNOSIS M
How do you approach patients with medically unexplained symptoms? Professor Chris Burton offers some insights
EDICALLY unexplained symptoms (MUS) is an umbrella term commonly used to refer to physical symptoms in the absence of a diagnosed organic disease. It includes both individual symptoms (e.g. headache or abdominal pain) and syndromes (e.g. tension type headache or irritable bowel syndrome). An estimated 20 to 30 per cent
of consultations in primary care involve patients experiencing MUS with no clear diagnosis. Recent developments in neuroscience and physiology mean we are becoming increasingly able to explain these symptoms, and the term MUS should probably be abandoned: both because it’s no longer accurate and patients dislike the term. However, it is still in use and these symptoms cause distress to patients, concern to doctors and occasionally lead to medico-legal consequences. For these reasons, it is important to think about what these symptoms are and how to manage them safely and effectively.
SYMPTOM MECHANISMS Current thinking about symptoms takes a similar approach to the definition of pain: symptoms can be thought of as bodily sensations which indicate the presence or possibility of disease. Symptoms are sensed in the brain and all symptoms, whether explained or unexplained by disease, involve both peripheral and central processes. In some symptoms, for instance an injured limb, it is simple to separate the peripheral and the central. We can see the injury which is triggering pain-sensing peripheral nerves and we know in turn that these nerves activate brain circuits which provide automatic protective responses (e.g. withdrawal) and a feeling of pain. For a patient with irritable bowel syndrome it is more difficult to separate the central and the peripheral. Visceral nerves may be triggered by modest changes in distension (perhaps in response to fermentation products of gut bacteria to certain foods) and in turn they activate brain circuits which also provide protective responses and feelings. But those circuits may, because of biology, past events or current concerns, be sensitised to produce a response which is more intense or more prolonged than expected from the size of the stimulus. This model of peripheral triggers with central amplification can be applied to most symptoms. The key point is that medically “unexplained” symptoms involve disproportionate central processes relative to the peripheral triggers when compared to “explained”
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diseases. This central processing approach is replacing older views that MUS represent the result of somatisation – the expression of mental distress as physical symptoms. While common mental disorders do have an increased prevalence in patients with MUS, the relationship between the two is complex and there is strong evidence that causes apply in both directions – symptoms can lead to distress and distress can amplify symptoms.
SAFETY IN DIAGNOSIS There are good guidelines for common MUS syndromes which include clear diagnostic criteria. These guidelines and criteria are useful for setting practice protocols and are also a valuable resource for occasional use – to look up information about specific syndromes. Guidelines typically recommend appropriate screening tests to exclude other conditions. Carrying these out (and documenting their use) is a valuable way of ensuring safe practice in this area of inherent uncertainty.
In less specific symptoms it is important to look for (and document) both the absence of features of peripheral disease and the presence of features suggesting increased central processing. Positive indicators of heightened central processing include symptom features which are biologically implausible (e.g. non-anatomic pain distribution), signs of sensitisation such as the presence of allodynia or abdominal wall tenderness (Carnett’s sign) and the occurrence of symptoms on examination despite signs of normal function (e.g. during a stepping test for dizziness). The level of distress is generally not a helpful measure in deciding whether a symptom is due to organic disease or not.
Clinicians often worry about missing organic disease due to gaps in their knowledge but there is evidence that mistakes are much more likely to be due to errors in thinking about clinical features (for instance closing down a differential diagnosis too early) than to gaps in knowledge or faulty examination technique. Investigations have a mixed role in patients with suspected medically unexplained symptoms. Simple investigations (e.g. full blood count or C-reactive protein) represent an important safety net for patients with uncertain symptoms and, along with documentation of weight, represent an important part of safe management. On the other hand investigations “to reassure the
patient” have very little value. Negative tests may reassure doctors (sometimes falsely) but there is good evidence from a systematic review that diagnostic tests produce
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