Linkage data have now identified several inflammatory bowel disease (IBD) susceptibility loci but these data have not been consistently replicated in independent studies. One potential explanation for this is the possibility that patients enrolled in such studies may have been erroneously classified with respect to their diagnosis.
To determine the rate and type of misclassification in a large population of individuals referred for participation in an IBD genetics study and to examine the effect of diagnostic misclassification on the power to detect linkage.
The medical records of 1096 patients entered into an IBD genetics programme were reviewed using standardised diagnostic criteria. The original patient reported diagnoses were changed, if necessary, based on review, and the reasons for the change in diagnosis were recorded. To evaluate the effect of misclassification on linkage results, simulations were created with Gensim and analysed using Genehunter to evaluate a model for IBD inheritance.
Sixty eight of 1096 (6.2%) individuals had a change in diagnosis from that originally reported. The majority of changes were patients with either Crohn's disease or ulcerative colitis who were determined not to have IBD at all. The principal reasons for changes to the original diagnosis were discordance between the patients' subjective reports of diagnosis and actual clinical history, endoscopic, or pathological results; a change in disease pattern over time; and insufficient information available to confirm the original diagnosis. A 10% misclassification rate resulted in 28.4% and 40.2% loss of power to detect a true linkage when using a statistical model for a presumed IBD locus with lambda(s) values of 1.8 and 1.3, respectively.
Diagnostic misclassification occurs in patients enrolled in IBD genetic studies and frequently involves assigning the diagnosis of IBD to non-affected individuals. Even low rates of diagnostic misclassification can lead to significant loss of power to detect a true linkage, particularly for loci with modest effects as are likely to be found in IBD.
In the decades since the major forms of idiopathic inflammatory bowel disease were defined on the basis of clinical manifestations, investigators have been challenged to identify the fundamental pathophysiologic processes underlying these enigmatic disorders, and clinicians have struggled to provide effective therapy for the often dismaying clinical manifestations. Clinical experience has led to the generally accepted notion that Crohn's disease and ulcerative colitis are distinct, if not discrete, entities. However, whether these are fundamentally different diseases or part of a mechanistic continuum remains an unanswered question, with both conceptual and practical management implications.
Crohn's disease is a heterogeneous entity. Previous attempts of classification have been based primarily on anatomic location and behavior of disease. However, no uniform definition of patient subgroups has yet achieved broad acceptance. The aim of this international Working Party was to develop a simple classification of Crohn's disease based on objective variables. Eight outcome-related variables relevant to Crohn's disease were identified and stepwise evaluated in 413 consecutive cases, a database survey, and by clinical considerations. Allocation of variables was conducted with well-defined Crohn's disease populations from Europe and North America. Cross-table analyses were performed by chi-square testing. Three variables were finally elected: Age at Diagnosis [below 40 years (A1), equal to or above 40 years (A2)], Location [terminal ileum (L1), colon (L2), ileocolon (L3), upper gastrointestinal (L4)], and Behavior [nonstricturing nonpenetrating (B1), stricturing (B2), penetrating (B3)]. The allocation of patients to these 24 subgroups proved feasible and resulted in specific disease clusters. Cross-table analyses revealed associations between Age at Diagnosis and Location, and between Behavior and Location (all p < 0.001). The Vienna classification of Crohn's disease provides distinct definitions to categorize Crohn's patients into 24 subgroups. Operational guidelines should be used for the characterization of patients in clinical trials as well as for correlation of particular phenotypes with putative biologic markers or environmental factors.
A crucial step in the development of clinical trials to determine the efficacy of various therapies for inflammatory bowel disease (IBD) has been the creation of activity indices. This article reviews the major components and operating characteristics of clinical activity indices commonly used in randomized, controlled trials of IBD therapy. In addition, the paper provides a brief overview of the developmental requirements for any new index.
Nonvalidated definitions of disease-related parameters in inflammatory bowel disease cause variations in diagnosis and disease classification. We determined interobserver agreement on applications of definitions of the Vienna Classification variables and computed the potential influence of misclassification on genotype/phenotype associations.
Ten records of patients with Crohn's disease (CD) were independently evaluated by 19 observers using a standardized inflammatory bowel disease documentation system, which included the Vienna Classification. Interobserver agreement (IOA) was calculated as a percentage of the observers' agreement with a predetermined reference observer and by Cohen's kappa. Randomized reclassifications were then computed with 10,000 simulation runs using the IOA results and published NOD2/CARD15 gene status. A chi-square independence test was calculated for each simulation run.
IOA for location and behavior was 70% (K = 0.57) and 95% (K = 0.91), respectively. IOA for location subgroups ranged from 48% to 88% and for behavior from 91% to 97%. By including the results of histopathology into the evaluation of location, the overall IOA increased significantly, to 80% (P = 0.019). Assuming a true genotype/phenotype association, the proportion of studies with nonsignificant findings (P > 0.05) because of the observed misclassification of location ranged from 13.3% to 63.8% and of behavior from 0.2% to 22.2%, depending on a study sample size of 500 or 150 patients respectively.
We concluded that there is appreciable interobserver disagreement on the location of CD according to the original Vienna Classification that may obscure true genotype/phenotype associations. Definitions of disease parameters have to be validated before being used as the bases for classifications.