The second most common cause of AD is pain or irritation within the colorectal area. Constipation, hemorrhoids, and anal fissures, all frequently observed in patients with SCI, contribute to episodes of AD (Teasell et al. 2000; McGuire & Kumar 1986; Hawkins et al. 1994; Teichman et al. 1998). Digital stimulation, a common component of bowel routines in individuals with SCI, can also trigger AD (Furusawa et al. 2007), especially in the presence of hemorrhoids and/or anal fissures. In addition, rectosigmoid distension and anal manipulation are common iatrogenic triggers of AD (Cosman & Vu 2005).
In two small RCTs (n=70) (Cosman & Vu 2005; Cosman et al. 2002), investigators compared the effect of topical local anesthesia of the anorectal area to a nonmedicated control gel for the prevention of AD during anorectal procedures. They found that anoscopy, which involves stretching the anal sphincters, was a more potent stimulus for AD than flexible sigmoidoscopy, which involves gaseous distention of the rectosigmoid. In one randomized, double-blind, placebo-controlled trial, AD was not abolished by topical lidocaine in the rectum during the anorectal procedure (Cosman et al. 2002). However, the same investigators in a later RCT demonstrated that intersphincteric anal block with lidocaine was effective in limiting anorectal procedure-associated AD (Cosman & Vu 2005). In one small RCT (n=25) (Furusawa et al. 2009) investigators found that topical lidocaine applied to the rectum prior to digital bowel stimulation significantly reduced systolic blood pressure and reports of AD over the duration of the bowel program when compared to the control group.
There is level 1 evidence (from 1 RCT: Cosman & Vu 2005) that lidocaine anal block significantly limits the AD response in susceptible patients undergoing anorectal procedures.
There is level 1 evidence (from 1 RCT: Cosman et al. 2002) that topical lidocaine does not limit or prevent AD in susceptible patients during anorectal procedures.
There is level 1 evidence (from 1 RCT: Furusawa et al. 2009) that topical lidocaine may help to prevent AD during gentle bowel stimulation.