Diagnostic disagreement between tests of evacuatory function: a prospective study of 100 constipated patients

Background: Evacuatory dysfunction (ED) is a common cause of constipation and may be sub-classified on the basis of specialist tests. Such tests may guide treatment e.g., biofeedback therapy for ‘functional’ defecatory disorders (FDD). However, there is no gold standard, and prior studies have not prospectively and systematically compared all tests that are used to diagnose forms of ED. Methods: One hundred consecutive patients fulfilling Rome III criteria for functional constipation underwent four tests: expulsion of a rectal balloon distended to 50 mL (BE₅₀) or until patients experienced the desire to defecate (BE_DDV), evacuation proctography (EP) and anorectal manometry. Yields and agreements between tests for the diagnosis of ED and FDD were assessed. Key Results: Positive diagnostic yields for ED were: BE_DDV 18%, BE₅₀ 31%, EP 38% and anorectal manometry (ARM) 68%. Agreement was substantial between the two balloon tests (k = 0.66), only fair between proctography and BE₅₀ (k = 0.27), poor between manometry and proctography (k = 0.01), and there was no agreement between the balloon tests and manometry (k = −0.07 for both BE₅₀ and BE_DDV). For the diagnosis of FDD, there was only fair agreement between ARM and EP (k = 0.23), ARM ± BE₅₀ and EP (k = 0.18), ARM and EP ± BE₅₀ (k = 0.30) and ARM ± BE₅₀ and EP ± BE₅₀ (k = 0.23). Conclusions & Inferences: There is considerable disagreement between the results of various tests used to diagnose ED and FDD. This highlights the need for a reappraisal of both diagnostic criteria, and what represents the ‘gold standard’ investigation.