Linear discriminant analysis of symptoms in patients with chronic constipation

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Abstract
The aim of this study was to devise a symptom scoring system to assist in diagnosing constipation and in discriminating among pathophysiologic subgroups. A structured symptom scoring questionnaire (11 questions) was completed by 71 chronically constipated patients and by 20 asymptomatic controls. The symptom score was correlated with a previously validated constipation score (Cleveland Clinic Score). All patients underwent colonic transit studies, standard anorectal physiology testing, and evacuation proctography. On the basis of these investigations alone, an observer blinded to the questionnaire results allocated patients to one of three pathophysiologic subgroups: slow-transit constipation, rectal evacuatory disorder, or mixed (slow-transit constipation and rectal evacuatory disorder). Linear discriminant analysis was used to assess the ability of different questionnaire symptoms to discriminate among these subgroups. Total symptom score was strongly correlated with the Cleveland Clinic Score (r = 0.9). The median total score in constipated patients was 20 (range, 11-35) compared with a median of 2 in controls (range, 0-6). Discriminant analysis using cross validation estimated that pathophysiology could be predicted correctly for 55 percent (95 percent confidence interval = 43-67 percent) of patients using just five symptoms. The discriminant function rarely misclassified patients with rectal evacuatory disorder as slow-transit constipation and vice versa, but could not effectively discriminate between patients with single and mixed pathologies. This new scoring system is a valid technique to assist in the diagnosis of constipation and is the first study using appropriate statistical methodology to demonstrate a discriminatory ability of multiple symptoms in constipation. At present, symptom analysis does not adequately differentiate major pathophysiologic subgroups for use in clinical practice.