Structural Abnormalities May Cause Failed Balloon Expulsion Test in the Absence of Dyssynergic Defecation

Introduction: An important cause of chronic constipation is obstructed defecation related either to structural pathology or dyssynergic defecation. The balloon expulsion test (BET) is a commonly used test for assessing defecatory dysfunction in combination with anorectal manometry (ARM) and electromyography (EMG). BET is inexpensive and studies have demonstrated high specificity for diagnosing obstructed defecation. However, there remains limited data on the subset of patients with abnormal BET, but normal ARM/EMG studies and the possible causes and significance. Methods: Adult patients referred to our tertiary motility center over the past year primarily for chronic constipation who underwent ARM, EMG, and BET were evaluated in our retrospective study. Patients with an abnormal BET (i.e. unable to evacuate the balloon within 1 or 2 minute cutoffs) and no dyssynergia on ARM or EMG (i.e. >20% sphincter relaxation during simulated defecation with appropriate rise in rectal pressure) were specifically identified. ARM, EMG and BET were performed using previously described standard techniques. Patients underwent lower endoscopy to rule out local pathology and some patients also underwent defecography. Results: A total of 8 patients were identified as having abnormal BET with normal ARM/EMG studies without any dyssynergia. 7 of 8 patients had BET > 2 minutes with 1 of 8 patients with a BET > 1 minute, all indicating abnormal studies. 4 of these patients (50%) were ultimately found to have anatomic or structural lesions that could explain these findings. 2 patients were found to have anal stenosis likely due to prior hemorrhoidectomy found on exam under anesthesia. Another patient was found to have a pouchocele during lower endoscopy that was confirmed on defecography. The last patient was noted to have rectal prolapse with intra-anal mucosal intussusception. No explanation for the discrepancy was found in the remaining 4 patients including no evidence of ineffective straining. Conclusion: BET remains a useful diagnostic tool for obstructed defecation, but still should be used in conjunction with ARM/EMG. There are false-positive BET studies with normal ARM/EMG results, which in part may be explained by structural abnormalities not seen on ARM/EMG. Additional diagnostic modalities such as anal endosonography, defecography, or exam under anesthesia may clarify the underlying pathology in this subset of patients.