Evaluation of the paradoxical sphincter contraction by a strain/squeeze index in constipated patients.

Purpose: One finding in patients with constipation is the paradoxical puborectalis contraction, i.e. , activation of the sphincter muscles during straining instead of relaxation. The aims of this study were to evaluate the importance of needle placement in sphincter-electromyography and to evaluate a strain/squeeze index in constipated patients and control subjects.

Methods: We investigated consecutively 194 constipated patients and 16 control subjects with integrated electromyography during straining and squeezing and calculated a strain/squeeze index. The examination was performed in the puborectalis and in the external anal sphincter muscle through hook-electrodes.

Results: There was a strong correlation between indices in the puborectalis muscle and in the external anal sphincter muscle (r = 0.70-0.80, P < 0.001). Forty-seven patients (24 percent) had a mean index of greater than 50 compared with none in the control group (P = 0.01). Mean overall index in patients was 24 (range, 0-306) vs. 18 (range, 0-45) in controls (P = 0.12). Patients with an index greater than 50 had impaired rectal evacuation (P < 0.001), increased threshold for urge (P < 0.05), and tended to have fewer stools (P = 0.06).

Conclusion: Quantification of paradoxical contraction in the puborectalis and external anal sphincter with a strain/squeeze index differentiates patients in whom paradoxical activity may be a cause of constipation. An index above 50 may be of pathologic significance. Correlations between activity in the puborectalis and external anal sphincter muscle were strong which suggests that investigation in one of them is sufficient.