Isolated colonic inertia is not usually the cause of chronic constipation.

AIM: Chronic constipation is classified as outlet obstruction, colonic inertia or both. We aimed to determine the incidence of isolated colonic inertia in chronic constipation and to study symptom pattern in those with prolonged colonic transit time.
METHODS: Chronic constipation patients were classified radiologically by surgeon-reported defaecating proctography and transit study into four groups: isolated outlet obstruction, isolated colonic inertia, outlet obstruction plus colonic inertia, or normal. Symptom patterns were defined as stool infrequency (twice weekly or less) or frequent unsuccessful evacuations (more than twice weekly).
RESULTS: Of 541 patients with chronic constipation, 289 (53%) were classified as isolated outlet obstruction, 26 (5%) as isolated colonic inertia, 159 (29%) as outlet obstruction plus colonic inertia and 67 (12%) as normal. Of 448 patients (83%) with outlet obstruction, 35% had additional colonic inertia. Only 14% of those with prolonged colonic transit time had isolated colonic inertia. Frequent unsuccessful evacuations rather than stool infrequency was the commonest symptom pattern in all three disease groups (isolated outlet obstruction 86%, isolated colonic inertia 54% and outlet obstruction plus colonic inertia 63%).
CONCLUSION: Isolated colonic inertia is an unusual cause of chronic constipation. Most patients with colonic inertia have associated outlet obstruction. These data question the clinical significance of isolated colonic inertia.