Abstract:
The purpose of this study was to prospectively evaluate the application of the cognitivebehavioural
model to two common functional somatic syndromes: irritable bowel
syndrome (IBS) and chronic fatigue syndrome (CFS). A range of predisposing,
precipitating and perpetuating variables operationalised from this model were assessed in
two acutely ill samples. The significance and relative importance of these variables with
regard to the development of post-infectious IBS and CFS were then examined. At the
same time, information was gathered to assess the appropriateness of an overall
conceptualisation for the functional somatic syndromes. Similarities and differences
between the two syndromes were investigated, and the impact of differing thresholds and
disability criteria were compared to determine the utility of current diagnostic criteria.
Patients with a positive laboratory test result for Campylobacter gastroenteritis or
glandular fever were recruited through general practitioners. A total of 1018 participants
completed a baseline questionnaire at the time of infection which included measures of
anxiety, depression, perfectionism, somatisation, perceived stress, acute illness perceptions
and illness related behaviours. Those previously diagnosed with CFS or IBS were
excluded, along with participants experiencing any medical condition known to impact on
fatigue levels or bowel function (n=183). Participants completed follow-up questionnaires
at three (93% response rate) and six months (90% response rate) post-infection. At each
point, cases of IBS and CFS were identified using published diagnostic criteria.
Results indicated that a range of cognitive, behavioural, physiological and emotional
variables were significantly related to the development of both IBS and CFS. Whilst there
were some similarities between the two conditions, there were also some key differences.
Depression and somatisation were significant predisposing variables in the development of
CFS, but not IBS, for which anxiety was a key predictor. Perceived stress and the type of
acute infection were more important as precipitants of IBS than CFS. Campylobacter was
a significant predictor of IBS at both timepoints, whilst the presence of this illness type
also strengthened the association between IBS and the psychological variables. In contrast,
glandular fever was a significant predictor of CFS at three months only, and this
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association was outweighed by the inclusion of the psychological variables. With regard to
perpetuating factors, negative illness perceptions at the time of acute infection were
significantly related to both conditions, and all-or-nothing behaviour was also associated
with IBS. When CFS and IBS cases at six month follow-up were compared, CFS cases
had higher levels of disability, but not health care utilisation. Finally, when subthreshold
cases of IBS and CFS were compared to their diagnosed counterparts, on the whole they
did not differ with regard to the psychological risk factors, disability or health care
utilisation.
These results support the application of the cognitive-behavioural model to IBS and CFS
as a useful explanatory tool and guide for treatment. The results provide a degree of
empirical detail that has previously been lacking with regard to these models. Comparing
the application of the model to two separate conditions has demonstrated subtle but
important differences between the development of post-infectious IBS and CFS. These
findings suggest that an overall conceptualisation for the functional somatic syndromes
may not be capable of determining and addressing such differences for individual
conditions. With regard to the diagnostic criteria for IBS and CFS, results suggest that the
current criteria may be unnecessarily restrictive and complex. Simplification or the
formalised addition of subthreshold conditions may result in more widespread usage and
clinical applicability of these criteria.