Alteration of the spinal modulation of nociceptive processing in patients with irritable bowel syndrome

Visceral hypersensitivity has been evidenced in patients with irritable bowel syndrome (IBS) but its mechanisms remain poorly elucidated. We investigated the spinal transmission of nociceptive signals in IBS patients by analysing the effects of rectal distensions on electromyographic recordings of the somatic nociceptive flexion (RIII) reflex, an objective index of spinal nociceptive processes.

Fourteen IBS and 10 healthy volunteers were included in the study. Slow ramp (40 ml/min) and rapid phasic (900 ml/min, 10, 20, 30, and 40 mm Hg) rectal distensions were randomly performed while the RIII reflex evoked by electrical stimulation of the sural nerve at the ankle was continuously recorded from the ipsilateral biceps femoris.

In healthy volunteers, significant progressive inhibition of the RIII reflex was observed during slow ramp distension (61 (13)% of control values) while biphasic effects (facilitation and inhibition) were observed during rapid distensions. In contrast, in IBS patients, the RIII reflex was significantly facilitated during slow ramp distension (139 (15)% of control values) and inhibitions induced by rapid distensions were significantly reduced. Volumes of distension and rectal compliance were similar in both groups.

Our results provide direct evidence that a hyperexcitability of spinal nociceptive processes is present in a large subgroup of IBS patients.