Anal ultra slow waves: a smooth muscle phenomenon associated with dyschezia

Anal ultra slow waves (USWs) have been described in a variety of anorectal disorders, all of which may be associated with constipation. We investigated whether they represent a marker for dyschezia and whether their occurrence can be modified. Manometric and endosonographic studies were performed in 25 patients with dyschezia, in 25 age- and sex-matched controls, and in an equal number of patients with hemorrhoids. Patients exhibiting ultra slow waves were repeatedly studied with and without local administration of isosorbide dinitrate. In addition, we determined whether stimulatory maneuvers modify the occurrence of USWs. Anal USWs were persistently found in 56% of patients with dyschezia, in 8% of patients with hemorrhoids, and in none of the healthy controls. They were stimulated by anal squeeze and completely abolished by local administration of isosorbide dinitrate. Ultra slow waves always occurred in conjunction with an increase in anal resting pressure and were tightly associated with a fluctuation in slow wave amplitude. Anal sphincter morphology was similar in patients with dyschezia and in controls. We conclude that anal USWs occur most frequently in patients with dyschezia and indicate smooth muscle dysfunction. Treatment directed at abolishing this motor phenomenon may represent a novel approach to the management of patients with dyschezia.