Molecular and Cellular Characteristics of the Colonic Pseudo-obstruction in Patients With Intractable Constipation

Chronic intestinal pseudo-obstruction (CIPO) is a disorder characterized by recurrent symptoms suggestive of obstruction such as abdominal pain, proximal distension with extremely suppressed motility in the absence of lumen-occluding lesion, whose etiology/ pathophysiology is poorly understood. In this study we investigated a functionally obstructive lesion that could underlie symptoms of CIPO.

We studied colons surgically removed from 13 patients exhibiting clinical/pathological features of pseudo-obstruction but were unresponsive to standard medical treatments. The colons were characterized morphologically, functionally and molecularly, which were compared between regions and to 28 region-matched controls obtained from colon cancer patients.

The colons with pseudo-obstruction exhibited persistent luminal distension proximally, where the smooth muscle was hypertrophied with changes in the cell phenotypes. Distinct luminal narrowing was observed near the distal end of the dilated region, close to the splenic flexure, previously referred to as the "transition zone (TZ)" between the dilated and non-dilated loops. Circular muscles from the TZ responded less to depolarization and cholinergic stimulation, which was associated with downregulation of L-type calcium channel expression. Smooth muscle contractile protein was also downregulated. Myenteric ganglia and neuronal nitric oxide synthase (nNOS) positive cells were deficient, more severely in the TZ region. Interstitial cells of Cajal was relatively less affected.

The TZ may be the principal site of functional obstruction, leading to proximal distension and smooth muscle hypertrophy, in which partial nNOS depletion could play a key role. The neuromuscular abnormalities probably synergistically contributed to the extremely suppressed motility observed in the colonic pseudo-obstruction.