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The European Journal of Psychiatry

versión impresa ISSN 0213-6163

Eur. J. Psychiat. vol.21 no.1 Zaragoza ene./mar. 2007




Improving the Classification of Medically Unexplained Symptoms in Primary Care



M. Rosendal, PhD, MD, Senior Researcher*; P. Fink, MD, Dr Med Sci, PhD, Senior Lecturer, Research Director**; Erik Falkoe, MD***; Henriette Schou Hansen, MD**; F. Olesen, MD, Dr Med Sci, Prof, Research Director*

* Research Unit and Institute for General Practice, Aarhus University
** Research Clinic for Functional Disorders, Aarhus University Hospital
*** Research Unit for General Practice, University of Southern Denmark

Address for correspondence




Background: Many patients in primary care complain of physical symptoms not attributable to any known conventionally defined disease, i.e. medically unexplained symptoms (MUS).
Objectives: This paper aims to present the problems with our current classification of MUS in general practice and propose new criteria for the classification of Medically Unexplained Symptoms in a future edition of the International Classification of Primary Care (ICPC).
Methods: Discussion of European classification systems in relation to current evidence about MUS in primary care.
Results: At present, clinical care and research are hampered by the lack of a valid and reliable diagnostic classification of MUS. A particular problem in primary care is that the diagnostic category of somatoform disorders only includes persistent cases and therefore offers no opportunity for the classification of many patients with MUS in general practice. We propose new diagnostic criteria for MUS that can easily be integrated in a future edition of the ICPC. The criteria introduce mild to moderate MUS into the chapter of general and unspecified health problems if the patient has at least three MUS during an episode of care, whereas severe conditions are kept in the psychological chapter under the diagnoses applied until now.
Conclusion: A diagnosis and classification of MUS is essential for the prediction of prognosis and the choice of appropriate care for these patients in general practice. It remains to be evaluated in epidemiologic research whether the proposed classification criteria fulfil this purpose.

Key words: Diagnosis, Classification, Primary health care, Somatoform disorder, symptoms and signs, ICPC.



It has become increasingly clear that our present diagnoses and classifications of Medically Unexplained Symptoms (MUS) do not match the problems presented by patients in primary health care1-3. Fundamental issues on classification of MUS in general practice need to be better described and become more operational in order to improve clinical care, education and research in this field.

This article will present the clinical picture in general practice and some of the problems encountered when the current European classification is used for patients with MUS in this setting. Finally, we will present new criteria for MUS that could be included in a future edition of the International Classification of Primary Care4.


The picture of Medically Unexplained Symptoms in primary care

The concept MUS may be defined as "conditions where the patient complains of physical symptoms that cause excessive worry or discomfort or lead the patient to seek treatment but for which no adequate organ pathology or patho-physiological basis can be found5. This definition has been chosen because it is purely descriptive but other names and definitions ex-ist6,7.

The experience of bodily sensations and symptoms is common8, and most people handle their symptoms without the involvement of the health care system. The minority of patients (about 30%) who seek help are mainly cared for in primary care (about 96%). Only about 1% of people with physical symptoms are seen in specialised care8. The general practitioner (GP) is working in the borderland between normality and severe illness and therefore most of the symptoms met in primary care don't fit into the classification systems developed in specialised settings.

We may see MUS as a spectrum of disorders ranging from mild physical symptoms to serious conditions that cause suffering and disablement9. At some point in this spectrum the symptoms will have an impact that makes the affected person visit the health care system - usually a GP. At yet another point the impact is so severe that the patient is better cared for in a specialised setting. Table I presents vignettes representing this spectrum of MUS in general practice.

The prevalence depends on which part of the spectrum is under study. Kroenke and Mangelsdorff studied common physical symptoms among patients in an outpatients' clinic in the US. Seventy-four percent of these symptoms remained medically unexplained during 3 years of follow-up10. The ICD-10 criteria for somatoform disorders (criteria in Table II) have been applied in the GPs' waiting rooms in European studies. The prevalence of somatoform disorders was 16-35% and somatisation disorder 6-10%3,11. If the 6 month limit of symptom duration was ignored, somatoform symptoms were encountered in 60% of all patients3 matching the findings in the US study. However, we do not know whether the affected patients actually saw their GPs for their somatoform symptoms or the reason for encounter was something different. GPs have been asked to estimate the prevalence of significant MUS. On average, they registered MUS in 10-20% of patients2,12, but between GPs there was a 10-fold variation in their diagnoses2. This variation was not explained by differences in patient populations, but was interpreted as a reflection of the GPs' different conception of where the diagnosis of MUS is placed in the spectrum of disorders.


Why we need a diagnosis and classification of Medically Unexplained Symptoms

GPs are often taught that they need to be aware of the "low prevalence epidemiology" in primary care - referring to the low prevalence of most organic diseases. Yet, at the same time GPs are also working in a high prevalence area of normal reactions and MUS and they must be aware of different implications of bodily symptoms than simply the presence or absence of disease. A diagnostic framework that includes the classification of MUS would provide construct that would help GPs conceptualize and communicate about these high prevalence phenomena. A very important aim of such a construct would be to acknowledge the problem and ensure professional and appropriate care for patients with MUS (clinical perspective). Furthermore, a diagnosis may enable quality improvement initiatives and rigorous research in the complex problems presented by MUS (research perspective). Finally, diagnoses may serve other purposes (patient perspective, social benefits etc.) which we have to bear in mind, but they are not our primary focus in this article.


How Medically Unexplained Symptoms are currently classified

The classification systems

WHO's International Classification of Disease (ICD) was developed in 1948 and is now in its 10th version. It is used throughout the health care systems in Europe, including primary care in some countries13, and it is also used as a golden standard for primary care research. WHO has provided a brief primary care version (ICD-10-PHC) that corresponds to the ICD-1014, but this version has not been widely implemented in European general practice. The predominant system in European primary care is the International Classification of Primary Care (ICPC) developed by the World Organisation of Family Doctors (Wonca) in 1987 and recognised as a WHO related classification for primary care in 200313. The ICPC aims to include diagnoses of yet unclarified and complex problems. The system is biaxial and contains 17 chapters (14 biomedical, one general, one psychological and one social) and 7 components (complaints or symptom diagnoses (1-29), process codes for prophylaxis, procedures, results, administration and referrals (30-69), and specific diagnoses (70-99). Component 1 (symptoms/complaints) and component 7 (diagnosis/disease) are mapped to ICD-10 and each rubric are provided with in- and exclusion criteria in the newest edition ICPC-24.

Other classification systems such as the Systematized Nomenclature of Medicine, Clinical Terms (SNOMED CT) and Read Codes are also in use13, and in the United States mental disorders are classified in a separate system: the Diagnostic and Statistical Manual for Mental Disorders (DSM-4)15 or the corresponding primary care version. The focus of this article is the ICD- and ICPC-systems.


The classification of Medically Unexplained symptoms

Both the ICD-10, ICD-10-PHC and the ICPC-2 classify MUS either in the psychiatric chapter or as syndrome diagnoses based on predefined symptom checklists and the exclusion of organ-pathology (Table II). However, the ICD and the corresponding specific diagnoses in the ICPC have been developed in specialized settings and therefore tend to be occupied with the extreme and chronic manifestations of MUS9. For example, symptom duration must be at least 6 months to fulfil the criteria for somatoform disorders. In a Danish study 76% of patients had shorter symptom duration according to the GPs' assessments16. Likewise, studies on health anxiety in primary care have shown that the 6 month duration criteria has been arbitrarily defined17. Consequently, the current classification leaves many primary care patients with MUS undiagnosed.

Moreover, the problem may be even more profound as it is now widely acknowledged among specialists in the field that "somatoform disorder" has failed as a diagnostic grouping18,19. In the ICPC this specific diagnosis is labelled P75 and involves the same problems as the ICD-10 diagnosis but furthermore, there is a problem with correspondence. P75 is named "somatisation disorder" in the ICPC-2 but actually includes all somatoform disorders, and the duration limit has been changed to 12 months instead of 6 months (Table II).

In conclusion, the ICD-10 systems and the specific diagnoses in the ICPC-2 cover only the minority of patients with severe MUS in primary care. Most patients with MUS and short symptom duration will be classified in the very heterogeneous group of symptom diagnoses or syndrome diagnoses.


Proposal for a new classification of Medically Unexplained Symptoms in the ICPC

A disorder is characterised by aetiology, symptom pattern, course, prognosis and outcome. With regard to MUS, problems are fundamentally heterogeneous and multi-factorial and the approach to classification will have to be pragmatic18 to ensure that the classification is acceptable and helpful to clinicians and patients. A relevant focus could be the classification's ability to predict prognosis -e.g. impairment/disability and health behaviours- and to assist the doctor in his/her choice of available treatment approaches.

In a previous article, we grouped patients with MUS according to severity (Fig. 1-2)9. Health advice refers to symptoms without significant impact on functioning or well-being and no indication for treatment or further investigations (example Anna, Table I). Natural (dis)stress reaction are reactions to life events and the distress does not exceed what would be expected from exposure to the stressor. Undifferentiated (dis)stress disorder or adjustment disorder includes patients who present non-specific physical, cognitive, emotional or behavioural symptoms with marked distress or significant impairment in social, occupational functioning or well-being (example Helen, Table I). Finally, the differentiated disorders are basically those classified in the ICD-10 and also include somatisation disorder in the ICPC (example Peter, Table I).

The ICPC already lays emphasis on codes for symptom diagnoses and these codes may be used for unexplained symptoms (A-Y 1-29). However, the symptom diagnoses also include symptoms under investigation, banalities or minor ailments where the GP find no indication for further intervention, along with mild MUS and persistent symptoms that remain unexplained (Figure 1). What we need is a more specific category for the unexplained symptoms that are neither self-limited nor fulfilling the criteria for persistent disorders. The challenge is how we distinguish self-limiting symptoms from clinical significant MUS.

Previous studies have demonstrated that the number of symptoms may be an indicator of severity and relates to physical functioning and health care utilization10,20-23. But the associations show no clear cut off for subgroups of severity and the number of symptoms chosen for classification will therefore be arbitrary. Previous studies have also specified particular symptoms related to somatoform disorders21,22,24. In line with this, a new empirical study about classification of bodily distress suggests that a minimum of 3 "non-specific symptoms" from a specified list form the diagnostic criteria23. This cut-point was chosen with a clinical perspective of specificity in mind. On this basis, we suggest an arbitrary cut-point of 3 symptoms for the diagnosis "MUS". Non-specific symptoms are found among the symptom diagnoses in the ICPC, but some symptom diagnoses may actually be specific (for example D13 jaundice). A list of non-specific symptom diagnoses would increase the reliability of the MUS diagnosis but implementation will depend on easy access via computer systems (Table III).

Besides symptom count, duration serves as a relevant distinction between mild and severe conditions. We have maintained the 6 months limit to separate mild from moderate conditions.

The aetiology of MUS is multi-factorial and in many cases unknown and complex. Although, psychological and social factors play an important role in some cases; they are, contrary to many doctors' conviction, not a precondition to classify symptoms as medically unexplained. Thus, the mild conditions in general practice do not naturally fall into the psychiatric chapter in the classification. Instead, we have maintained a descriptive definition and propose to place it in chapter A, general and unspecified health problems, in a future edition of the ICPC.

In conclusion, we suggest a description and classification of MUS relating to severity as described in detail in Table IV. We may also have to reconsider the name, and a suggestion is "Multiple Idiopathic Physical Symptoms". Furthermore, our proposal includes a change in the name and duration limit for somatisation disorder in the ICPC-2 in order to make this diagnosis correspond to the ICD-10. Finally, we suggest that somatoform disorders are split into two main categories: predominantly physical complaints and predominantly health anxiety (previous hypochondriacal disorder). The latter would include the most severe cases of MUS on the anxiety dimension and thus form the final point in the spectrum of symptom diagnoses describing fear of...



The presented classification (Table IV) includes mild-moderate conditions in addition to the severe conditions from our present classification systems. It is based on a descriptive approach and classifies milder conditions as general and unspecified health problems rather than psychological problems. This placement emphasizes the uncertain nature of mild MUS and makes the diagnosis more useful to GPs and less stigmatizing to patients. The proposed classification has not been empirically validated and it has yet to be evaluated whether it relates to disability and is able to predict prognosis and assign relevant treatment approaches (for example specific treatment for chronic disorders, reattribution models for moderate conditions and reassurance/normalisation for mild conditions). An evaluation should explore the conceptualization of the classification and the arbitrarily set cut points of 3 symptoms, 6 months and the symptom list.

The proposed classification contains positive criteria and may not include some patients with significant idiopathic symptoms. For example patients with single disabling symptoms will not be diagnosed until they fulfil criteria for somatoform disorders after 6 months. We need to know how large this group is and whether these patients need to be diagnosed with MUS at an earlier stage.

We have chosen a one-dimensional ap-proach to classification despite the complex nature of MUS. Multi-axial systems would give a more comprehensive understanding of bodily symptoms as they could focus on the three aspects of the bio-psycho-social model used in general practice25. However, the suggestion to apply a multi-axial classification is not appealing in primary care. GPs' consultations are very time-limited, so naturally, they wish to minimize the time spent on administrative procedures such as diagnostic coding.

Finally, the proposed criteria must be made operational by the integration into the GPs' electronic patient records. The computer systems may be programmed to react when at least 3 non-specific symptom diagnoses from the list are active (in episodes of care). This would prompt the GP to consider the diagnosis MUS and either accept or reject it. If electronic systems are not available we will expect a more pragmatic application of the criteria in daily practice.


Conclusion and perspective

Diagnosis is derived from the Greek words dia (between) and gignoskein (to know/distinguish) meaning "to know between". In relation to MUS we may have to reconsider our paradigm for diagnosis and differentiate between different treatment approaches rather than focus on organ pathology or symptom patterns. In order to make this differentiation, we may use prognostic factors such as symptom duration and number of symptoms for the classification of subgroups. The presented proposal for a new classification is differentiated, matches primary health care patient populations, builds on an existing classification system and is simple to understand and use. Furthermore, it provides a more balanced weight to medically unexplained symptoms and enables communication and research in primary care. However, to make progress in the care for patients with MUS we need rigorous evaluation of new classifications in empirical studies.



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 Address for correspondence:
Marianne Rosendal
Research Unit for General Practice
Vennelyst Boulevard 6, DK-8000 Aarhus, Denmark
Ph: +45 2041 1619 / +45 8942 6010
Fax: +45 8612 4788

Received 21 December 2006
Accepted 21 February 2007

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