Rectal cooling test in the differentiation between constipation due to rectal inertia and anismus

The differentiation between constipation due to rectal inertia and that due to outlet obstruction from non-relaxing puborectalis muscle (PRM) is problematic and not easily achieved with one diagnostic test. Therefore, we studied the hypothesis that the rectal cooling test (RCT) can effectively be used to differentiate between those two forms of constipation.

The study enrolled 28 patients with constipation and abnormal transit study in whom radio-opaque markers accumulated in the rectum; 15 healthy volunteers acted as controls. Electromyographic activity of the external anal sphincter (EAS) and PRM was initially recorded. Subsequently rectal wall tone was assessed by a barostat system during rectal infusion with normal saline at 30 degrees C and at 4 degrees C with simultaneous electromyography (EMG).

There was a significant increase in EMG activity of the EAS and PRM on strain- ing (p<0.001), suggestive of anismus, in 10 of 28 patients and 0 of 15 controls. Rectal tone in controls did not respond to saline infusion at 30 degrees C, but it increased at 4 degrees C (p<0.05). Similarly, in constipated patients rectal tone did not respond to rectal saline infusion at 30 degrees C, but infusion at 4 degrees C increased tone in all 10 patients with anismus (p<0.05); EMG activity of the EAS and PRM also increased (p<0.001). In the remaining 18 patients, rectal tone after saline infusion at 4 degrees C remained unchanged.

Rectal infusion with iced saline increased rectal tone in healthy controls and constipated patients with anismus while it had no effect in the remaining patients. Lack of increase of rectal tone may be secondary to rectal inertia. According to these preliminary observations, the rectal cooling test may be useful in differentiating between rectal inertia and anismus.