Clinical comorbidity was specific to disease pathology, psychologic distress, and somatic symptom amplification

Abstract

Objective

To test the hypothesis that disease pathology, psychologic distress, and somatic symptom amplification separately influence health care use by investigating the patterns of comorbidity in patients with diabetes, anxiety, and upper respiratory tract infection (URTI), respectively.

Methods

Adult diabetes (n = 4,365), anxiety (13,421), and URTI (9,854) cases, and 15,000 randomly selected controls were identified from a 1-year national survey of general practice consultations. Comorbidity was based on a standard clinical morbidity classification used by general practitioners in actual consultations.

Results

In case–control analyses of 122 morbidities, the number of significant comorbid associations (P < .01) for diabetes was 30, anxiety was 72, and URTI was 49. These associations showed significant heterogeneity in the odds ratios estimated using Cochran's Q and I² statistic, both between case groups and within each case group. Diabetes associations were stronger with peripheral vascular disease (odds ratio 2.7), candidiasis (2.5), cataract (2.4), obesity (2.2), and hypertension (1.7); anxiety with depressive disorder (4.1), affective psychosis (4.0), adjustment reaction (3.2), functional gastrointestinal disorders (2.5) and general symptoms (2.5); and URTI with nonspecific blood findings (5.5), bronchitis (5.2), and injury (3.5).

Conclusion

Our study shows patterns of clinical comorbidity specific to the case conditions that supports the hypothesis that different mechanisms (disease pathology, psychologic distress, and somatic symptom amplification) operate to influence consultation behavior and comorbidity.

Introduction

Some patients consult primary care regularly and about multiple problems. The reasons for such multiple consultations are likely to include the presence of underlying disease pathology, psychologic status, and the way in which common symptoms are interpreted, as well as attitudes towards health care. Disease pathology has been shown to have a high impact on health and health care use [1], [2], and multiple chronic diseases have been shown to be commonly prevalent together [3], [4]. Psychologic distress has been shown to play a key role in the presentation of symptoms [5], in somatization [6], and in association with specific medical conditions [7], [8]. An alternative but overlapping explanation to psychologic distress as a key factor in seeking consultation has been the concept of somatic symptom amplification. Whereas psychologic distress relates to mood and the associated negative affectivity or neuroticism, the concept of somatic symptom amplification is defined by hypervigilance of unpleasant body sensations and symptoms that may be weak but are perceived as pathologically abnormal [9]. Somatic symptom amplification also specifically relates to the enduring perceptual style or trait of the patient, which is independent of any coexisting psychologic distress, and which may be another reason as to why patients consult and consult with multiple problems.

Links between different morbidities and specified index conditions were originally defined by Feinstein as comorbidity [10]. Although patterns of comorbidity have been described for a range of chronic and psychologic disorders [11], [12], it is unclear whether these patterns are unique and distinct to that of the index condition or not, and whether the factors of disease pathology, psychologic distress, and somatic symptom amplification influence such comorbidity. Given the large range of different conditions and symptoms in the population [13], one might assume there would be little difference in the frequency and reasons for comorbid consultations related to these three factors.

Using indicative conditions to represent disease pathology, psychologic distress, and somatic symptom amplification, we have tested the hypothesis that there is no difference between these factors with respect to the associated comorbidity presented, using a national database of general practice consulters. In population-based general practice, the spectrum of problems seen ranges from symptoms, through self-limiting conditions, to chronic and life-threatening disorders [14], and this setting offers the opportunity to investigate the respective roles of these three factors. We have compared comorbidity in consulters with diabetes as an example of disease pathology, anxiety as an example of psychologic distress, and upper respiratory tract infection (URTI) as an example of somatic symptom amplification. URTI is a common self-limiting symptom that most people would not present to health care and which does not require specific intervention, and consultation with this condition was thus chosen as an indicator of somatic symptom amplification [15], [16]. The prior expectation was that diabetes would show the highest levels of comorbidity of a chronic disorder with cardiovascular disease [17], anxiety would show high levels of comorbidity across a range of conditions, both psychologic and clinical [12], [18], and upper respiratory tract infections lower levels of comorbidity generally [15], [16].

In the United Kingdom, all residents are registered with a family practitioner and so the clinical records in a general practice are a source of population-based data on all morbidity for which consultation is sought among its registered patients. Clinical records have been used to study health needs, health interventions, and health outcomes for individual diseases such as anxiety and depression [19] and diabetes mellitus [20]. Many practices code clinical contacts routinely using a standard classification that covers symptoms, minor illnesses, and chronic conditions. Such records of contact offer the potential to investigate consultations and the occurrence of comorbidity. We have used a large national database of such general practice records to describe the frequency and patterns of comorbidity, and to directly compare comorbidity associated with diabetes, anxiety, and URTI.