Patients seek help from doctors for symptoms and doctors
diagnose diseases to explain them. Symptoms are the
patient’s subjective experience of changes in his or her
body. Diseases are objectively observable abnormalities
i n the body. Difficulties arise when the doctor can find
n o objective changes to explain the patient’s subjective
experience. The symptoms are then referred to as
medically unexplained or functional.1Many different
functional syndromes have been described. In fact, each
medical specialty seems to have at least one: for
rheumatologists, prominent muscle pain and tenderness is
fibromyalgia; for gastroenterologists, abdominal pain with
altered bowel habit is irritable bowel syndrome; and for
infectious-disease specialists, chronic fatigue and myalgia is
a postviral or chronic fatigue syndrome (panel).
We postulate that the existence of specific somatic
syndromes is largely an artefact of medical specialisation.
That is to say that the differentiation of specific functional
syndromes reflects the tendency of specialists to focus on
only those symptoms pertinent to their specialty, rather
than any real differences between patients. To explore
t h i s hypothesis, we reviewed the research literature
w i t h regard to three questions. (1) Do the published
diagnostic criteria for each of the specific functional
syndromes overlap in their constituent symptoms? (2) Do
patients identified as having one functional somatic
syndrome also meet symptom criteria for others? (3)
A r e there similarities across syndromes in the non-
symptom characteristics of sex, coexisting emotional
disorder, proposed aetiology, prognosis, and response to
t r e a t m e n t ?
Various names have been given to medically unexplained
symptoms. These include somatisation, somatoform
disorders, medically unexplained symptoms, and
functional somatic symptoms. In this review, we use the
term functional somatic symptoms.1We define a functional
somatic symptom as one that, after appropriate medical
assessment, cannot be explained in terms of a
conventionally defined medical disease.
936 THELANCET • Vol 354 • September 11, 1999
Lancet 1999; 354: 936–39
Department of Psychological Medicine, Guy’s, King’s and
St Thomas’ School of Medicine, London, UK (Prof S Wessely MD,
C Nimnuan MB BS), and Department of Psychiatry, University of
Edinburgh, Kennedy Tower, Royal Edinburgh Hospital, Edinburgh
EH10 5HF, UK (M Sharpe MRCPsych)
Correspondence to: Dr M Sharpe
Functional somatic symptoms and syndromes pose a
major challenge to medicine. These symptoms are
common, frequently persistent, and are associated with
significant distress, disability, and unnecessary expenditure
of medical resources. In UK primary care, somatic
symptoms and syndromes account for 20% of
c o n s u l t a t i o n s .2Among medical outpatients, somatic
complaints accounted for 25% of new referrals in a Dutch
s t u d y3and for 35% in a UK study.4Even among medical
inpatients, a substantial proportion have complaints that
are found to be functional.5
Functional somatic symptoms are not only common,
they are also clinically important. The prevalence of
emotional distress and disorder in patients who attend
hospital with functional syndromes (such as irritable bowel
syndrome) is higher than in patients with comparable
medical conditions (such as inflammatory bowel disease).6
Furthermore, far from merely representing the “worried
well”, many such patients are severely disabled. For
example, chronic fatigue syndrome is associated with worse
disability than conditions such as heart failure.7
Conventional medical therapy is fairly ineffective for
these patients. The result is frustrated physicians and
disabled and dissatisfied patients with chronic symptoms.
In a follow-up study of patients with non-cardiac chest
pain, Potts and Bass8found that three quarters of patients
had symptoms more than 10 years after presentation.8
T h e resulting costs to patients and to the health system
a r e substantial, especially if patients undergo repeated
investigation and treatment in hospital. Thus, functional
somatic complaints constitute a large, clinically important,
Functional somatic syndromes: one or many ?
S Wessely, C Nimnuan, M Sharpe
We review the concept and importance of functional somatic symptoms and syndromes such as irritable bowel syndrome
and chronic fatigue syndrome. On the basis of a literature review, we conclude that a substantial overlap exists between
the individual syndromes and that the similarities between them outweigh the differences. Similarities are apparent in
case definition, reported symptoms, and in non-symptom association such as patients’ sex, outlook, and response to
treatment. We conclude that the existing definitions of these syndromes in terms of specific symptoms is of limited
value; instead we believe a dimensional classification is likely to be more productive.
Functional somatic syndromes by speciality
Gastroenterology Irritable bowel syndrome, non-ulcer
Gynaecology Premenstrual syndrome, chronic pelvic pain
Cardiology Atypical or non-cardiac chest pain
Respiratory medicine Hyperventilation syndrome
Infectious diseases Chronic (postviral) fatigue syndrome
Neurology Tension headache
Dentistry Temporomandibular joint dysfunction,
atypical facial pain
Ear, nose, and throat Globus syndrome
Allergy Multiple chemical sensitivity
and costly health-care issue that urgently requires better
understanding and improved management. But does the
current classification of such complaints into distinct
functional somatic syndromes aid or hinder this process?
Are there specific functional somatic
s y n d r o m e s ?
Each medical specialty has defined its own syndrome or
syndromes in terms of symptoms that relate to their organ
of interest. In addition, other more controversial
syndromes such as multiple chemical sensitivity and
repetitive strain injury have been proposed but less widely
accepted. Each syndrome tends to be regarded as a unique
diagnostic entity with its own special characteristics.
Furthermore, many of these syndromes are dignified by
their own formal case definition and body of research that
focuses solely on those patients identified as having the
syndrome. We question this orthodoxy and ask whether
these syndromes represent specific diagnostic entities, or
are they rather more like the elephant to the blind man—
simply different parts of a larger animal?
Hypothesis 1: overlap in case definitions of specific
s y n d r o m e s
We compared the case definitions of those functional
syndromes for which a published definition was available.
We found that even the so-called core or diagnostic
features of these syndromes overlap. For example, bloating
or a feeling of abdominal distention is reported in eight of
12 published case definitions for somatic syndromes, and
abdominal pain features in six. Headache is mentioned in
eight and fatigue in six (data available from authors). Our
hypothesis that there is substantial overlap in the case
definitions of specific functional somatic syndromes is
therefore supported by our review of published case
d e f i n i t i o n s .
Hypothesis 2: patients with one functional syndrome
frequently meet diagnostic criteria for other syndromes
Clinicians frequently observe that patients who meet the
criteria for specific functional syndromes report symptoms
other than those included in the case definition. A review
of the clinical research literature confirms this observation.
For example, many studies confirm that if patients who
meet the criteria for irritable bowel syndrome or non-ulcer
dyspepsia are asked about non-alimentary symptoms
(which they are usually not) they report them.
Furthermore, these other symptoms commonly include
ones that define different syndromes. Thus, patients with
irritable bowel syndrome may also have symptoms
indicative of atypical facial pain, chronic fatigue syndrome,
non-cardiac chest pain, food allergy, and chronic
hyperventilation (references available from authors). To
find out the extent to which this overlap occurs with
a l l t h e above syndromes, we carried out a series of cross-
referenced MEDLINE searches to look for papers that
sought to determine whether patients who had received a
diagnosis of one functional somatic syndrome also
r e p o r t e d symptoms of others. We found 13 references
f o r chronic fatigue syndrome that described symptoms
w h i c h overlapped with fibromyalgia, tension headache,
multiple chemical sensitivity, food allergy, premenstrual
syndrome, and irritable bowel syndrome. Conversely,
irritable bowel syndrome was linked with hyperventilation
syndromes, fibromyalgia, chronic fatigue syndrome,
tension headache, aytpical facial pain, non-cardiac chest
pain, chronic pelvic pain, non-ulcer dyspepsia, and
premenstrual syndrome (data available from authors).
These findings lend support to the hypothesis that
p a t i e n t s with one functional syndrome frequently meet
criteria for others.
Hypothesis 3: patients with different functional syndromes
share non-symptom characteristics
S e x—Almost all functional somatic symptoms are more
common in women than in men. In the large US
Epidemiological Catchment Area study,920 of 22 non-
menstrual somatic complaints were more common in
women than in men—the exceptions were chest pain and
difficulties with walking. Other investigations have reported
similar findings, even after the exclusion of gynaecological
d i s o r d e r s .1 0 , 1 1 This predominance of women also applies to
samples of patients selected on the basis of those who met
criteria for specific functional somatic syndromes. Clinical
studies of patients with chronic fatigue syndrome, irritable
bowel syndrome, temporomandibular joint dysfunction,
atypical facial pain, globus syndrome, and tension
headache have all shown that such symptoms predominant
among women. Even in community studies, women
predominate among patients with globus syndrome, irritable
bowel syndrome, chronic fatigue syndrome, non-ulcer
dyspepsia, fibromyalgia, and irritable bowel syndrome.
Emotional disorder—There is a strong association between
the range of functional somatic symptoms and
psychological distress. Russo and Colleagues1 2 showed that
the number of functional complaints was significantly
a n d positively related to the number of current and past
episodes of anxiety and depression. The findings of
c o m m u n i t y1 3 and primary-care studies1 4 , 1 5 also support a
close and linear relation between the number of somatic
symptoms and measures of emotional distress. Most
studies of emotional distress and disorder in patients
w h o attend hospital with a specific functional somatic
syndrome show a substantially increased rate of such
disorders, irrespective of whether the diagnosis is chronic
fatigue syndrome, multiple chemical sensitivity, or irritable
bowel syndrome. We are aware of only a handful o f
exceptions (references available from authors). Patients
who are identified in non-specialist settings as having
functional somatic syndromes are also likely to have an
increased rate of current and lifetime emotional distress
and disorder, but the association is usually weaker.
P h y s i o l o g y —Although there has been limited research into
the physiological mechanisms associated with functional
somatic symptoms, Sharpe and Bass1 6 report findings that
lend support to several identifiable mechanisms. These
findings serve to remind us that such complaints are not to
be regarded as “all in the mind”,1 7 and also suggest further
overlap between these syndromes. In the most general
sense, there is empirical evidence of a link between
functional somatic syndromes and altered functioning of
the central nervous system, which has gradually replaced
suggested abnormalities in specific organ systems. For
example, although muscle dysfunction was originally
suggested as the basis of chronic fatigue syndrome,
fibromyalgia, or both, this explanation has been
l a r g e l y replaced by an appreciation of the role of central
and neuroendocrine mechanisms. Indirect evidence of
abnormalities in serotonergic central-nervous-system
pathways has also been presented for several disorders,
THELANCET • Vol 354 • September 11, 1999 937
including non-nuclear dyspepsia, irritable bowel syndrome,
chronic fatigue syndrome, and premenstrual syndrome
(references available from authors).
History of childhood maltreatment and abuse—C h i l d h o o d
physical, and especially sexual, abuse is more common in
women with functional pelvic pain than in comparison
groups. This association does not seem to be specific,
however, and has also been reported in patients with
irritable bowel syndrome, premenstrual syndrome, tension
headache, fibromyalgia, and chronic fatigue syndrome.
Difficulties in doctor-patient relationship—C o m m o n a l t i e s
can also be observed across functional syndromes in the
interpersonal context, particularly in the doctor-patient
relationship that is frequently unsatisfactory for both
parties. Sharpe and colleagues1 8 reported that patients with
functional somatic symptoms were one of the three most
common types of “difficult to help” patients. Numerous
studies of individual syndromes, such as headache,
non-cardiac chest pain, fibromyalgia, and chronic fatigue
syndrome all reveal that dissatisfaction with medical care is
c o m m o n .
S u m m a r y —The hypothesis that patients with different
functional syndromes also share non-symptom characteristics
is therefore largely supported, although the available data are
inadequate to answer this question definitively.
Hypothesis 4: all functional syndromes respond to the
General approaches to management—Numerous guides
for the management of different functional somatic
syndromes provide remarkably similar advice. Although
subjected to only limited systematic evaluation, there are
many themes in common, such as the need to pay
attention to engagement, to explain the physiological
nature of symptoms, to limit investigations, and to
emphasise rehabilitation at the expense of cure.
Antidepressant drug treatment—Although there have been
too few studies to allow definitive statements about the
relative responsiveness of the various functional syndromes
to antidepressants, certain similarities, differences, and
uncertainties can be highlighted. For example, whereas
large well-conducted studies have established the
effectiveness of antidepressant drugs in premenstrual
syndrome, atypical facial pain, and non-cardiac chest pain,
their role in chronic fatigue syndrome and fibromyalgia
i s less clear, particularly with regard to the selective
serotonin-reuptake inhibitors (references available from
authors). The explanation for these differences is unclear
and may simply reflect the small number of trials.
Psychological therapies—Broadly defined psychological
treatment has been advocated for almost all the functional
somatic syndromes and has been shown to be effective in
many. Cognitive behavioural therapy is superior to
minimum care for most of the syndromes in which this
approach has been assessed, such as chronic fatigue
syndrome, premenstrual syndrome, irritable bowel
syndrome, and nearly all the various pain syndromes
(references available from authors).
S u m m a r y —There is a similarity in the treatments
recommended for patients with various functional somatic
syndromes. There is also much evidence of similarity in
response to treatment, although the existing evidence
a l s o points to some differences. For example, low-dose
hydrocortisone therapy is helpful in the management of
chronic fatigue syndrome,1 9 exercise is beneficial in
f i b r o m y a l g i a2 0 and mitral-valve prolapse,2 1 and mebeverine is
of value in irritable bowel syndrome.2 2 However, whether or
not these treatments truly are specific to certain syndromes
(which goes against our hypothesis), or are simply used only
in only specific clinical settings remains unclear. At present,
the hypothesis that all functional syndromes respond to the
same therapies seems to be partly supported.
Implications of the overlap in functional
If we accept that the specific functional somatic syndromes
as conventionally defined have much in common, what are
C l a s s i f i c a t i o n —The main implication for classification is
that the current practice of regarding patients with
diagnoses of different functional somatic syndromes as
having clinically significant differences is questionable.
Rather, such patients may have similar conditions or
variants of a general functional somatic syndrome. Do we
have a more meaningful way to subclassify patients? Four
approaches may be considered.
The first approach is based on apparent clustering
i n t h e existing case definitions. For example, chronic
fatigue syndrome, fibromyalgia, and irritable bowel might
form one cluster and non-cardiac chest pain and
hyperventilation another (panel).
The second approach is based on epidemiological data.
An empirical approach based on a mathemetical (latent
variable) analysis of the functional somatic symptoms of
primary-care patients in Montreal identified five distinct
factors: irritable bowel syndrome, fibromyalgia, chronic
fatigue syndrome, anxiety, and depression.2 3 H o w e v e r ,
these factors were also highly correlated which suggests
similarities between them.2 4
The third approach is to use one of the existing
psychiatric classifications that subclassify most functional
somatic syndromes into depressive, anxiety, and
somatoform syndromes; the latter category being
f u r t h e r subdivided into somatisation disorder and other
syndromes. This approach has some value in so far as
i t encourages the identification of psychological and
somatic symptoms and the diagnosis of potentially
treatable symptoms. It also allows the identification of
those patients who have longstanding multiple complaints,
so-called somatisation disorder, with a poor prognosis. We
suggest, however, that whatever system is chosen, a
classification based purely on symptoms is of limited value
and offers little clinically useful information about the
p a t i e n t s .
The fourth alternative to the diagnostic suggestions
outlined above is a multiaxial approach.2 5 We suggest such
a scheme may be of greater value to clinicians and
researchers because it provides a fuller description of the
patients and provides useful information for treatment.
The relevant axes should include number of symptoms and
their duration, associated mood disturbance, the
p a t i e n t s ’ attributions for the symptoms, and identifiable
physiological processes.2 5
T r e a t m e n t —Most research on treatment selects patients on
the basis of whether they meet criteria for a specific
functional syndrome. This practice has limited the number
of patients entered into trials and added a spurious
complexity to our understanding of treatment. If we accept
938 THELANCET • Vol 354 • September 11, 1999
that functional somatic syndromes are considered together,
we open the way to more general strategies and services for
C o n c l u s i o n
Functional somatic symptoms and syndromes are a major
health issue. They are common and may be persistent,
disabling, and costly. Most of the current literature
pertains to specific syndromes defined by medical
subspecialties. We have put forward the hypothesis that the
acceptance of distinct syndromes as defined in the medical
literature should be challenged. We contend that the
patients so defined actually have much in common. A
review of the published evidence largely supports our
suggestion. This hypothesis is open to further testing, and
we are currently attempting to do just that in a study across
We do not wish to suggest that the care of patients with
functional somatic syndromes should be transferred from
medicine to psychiatry—that would simply be replacing
one monolithic view with another. A more appropriate
position is to call for the return of a “general physician”
with a broad-based approach, perhaps aided by liaison
w i t h psychiatrists or psychologists. We propose an end to
the belief that each “different” syndrome requires its own
particular subspecialist adopting an idiosyncratic approach
in apparent isolation from work elsewhere.
Our thesis is not new. A previous generation of
physicians noted overlaps between what were then
deemed “psychosomatic syndromes”, and also recognised
the alternation or sequence of different syndromes in the
s a m e individual. Among these were Ryle’s multiple visceral
n e u r o s e s ,2 6 Halliday’s concept of psychosomatic
a f f e c t i o n s ,2 7 , 2 8 and Kissen’s theory of syndrome shift.2 9
Unfortunately, none of these general theories were
accompanied by empirical support, and consequently all
have disappeared from our current thinking on the subject.
We argue that their reinstatement is overdue.
A full list of citations for this paper, including the text and tables, is
a v a i l a b l efrom the authors, on request, or on The Lancet’s website
( h t t p : / / w w w . t h e l a n c e t . c o m ) .
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