PURPOSE: Paradoxical sphincter reaction is frequently found in constip
ated patients but sometimes also in incontinent patients and in asympt
omatic subjects. Its significance in defecation disorders has, therefo
re, been debated. The aim of the present study was to investigate whet
her paradoxical sphincter reaction is influenced by rectal filling vol
ume. PATIENTS AND METHODS: Eighteen patients with defecation disorders
and paradoxical sphincter reaction shown by electromyography were rei
nvestigated with an extended electromyographic investigation while in
the lying position and while in the sitting position, with 50-ml, 100-
ml, and 150-ml water-filled rectal balloons. RESULTS: All 18 patients
showing paradoxical sphincter reaction in the first investigation also
showed the reaction at the second investigation in the lying position
with a 0-ml volume of rectal contents. In the sitting position, with
a volume of 150 mi of rectal contents, the increase in electromyograph
ic activity disappeared in seven patients (39 percent) and no longer s
howed paradoxical sphincter reaction. Electromyography showed decrease
d activity in one patient and unchanged activity in six patients durin
g straining. A closing reflex was seen after completed straining in al
l of these seven patients. CONCLUSIONS: The present study demonstrates
that paradoxical sphincter reaction diagnosed by electromyography is
influenced by the rectal filling volume and might diminish when the re
ctum is filled with contents. The conventional electrophysiologic tech
nique in the diagnosis of paradoxical sphincter reaction might, theref
ore, overdiagnose this condition.