Toilet training one's child is a nearly universal challenge for parents, but is a particularly distressing ordeal for parents of individuals with autism spectrum disorder (ASD). Whereas typically developing children generally stop having daytime toileting accidents (i.e., they achieve continence) by 2-4 years of age, most individuals with ASD are either delayed in their acquisition of toileting skills, or never achieve continence. Furthermore, toileting concerns are a significant contributor to the increased stress experienced by caregivers of those with ASD. Besides dramatically increasing their burden of care, not being fully toilet trained negatively impacts the individual with ASD's hygiene, self-confidence, physical comfort, and independence while also causing social stigma. Incontinence can also have serious collateral consequences, such as limiting exposure to important life experiences. Furthermore, without effective treatment these problems generally persist into adulthood.

One reason why strictly behavioral treatments of encopresis have shown only limited success may be due to the fact that it often has a medical etiology. Encopresis is when underwear are soiled by stool in children over the age of toilet training and long-standing constipation is the cause of encopresis in the majority of children who exhibit it. Children with ASD are more likely to have constipation than typically developing children. Constipation causes encopresis by creating a cycle of withholding bowel movements (withholding is the voluntary contraction of the external sphincter to avoid a bowel movement): constipation causes painful bowel movements, which triggers further withholding behavior, exacerbating constipation. Over time the colon adapts by dilating, which leads to larger fecal masses in the rectum. Thus, the passage of larger and harder (i.e., painful) stools further increases an individual's withholding behavior. Over time, the rectum and colon become so dilated that the individual loses sensation. With no urge to defecate, an individual is even more likely to have stool accumulate in the rectum and is also unable to control bowel movements. Looser stool may leak around hard stool leading to an unintended leakage and sometimes large evacuation of stool occurs without the individual realizing it.

Although purely medical approaches can successfully treat constipation in individuals with ASD, they have not shown long term success with encopresis. That is, medical approaches can treat a single episode of constipation, but without acquiring toileting skills, the individual is likely to become constipated again, repeating the cycle. Conversely, purely behavioral strategies have not been shown to be effective at treating encopresis in individuals with ASD, even when they are not experiencing constipation. One reason for this lack of success may have to do with the fact that it is often difficult to predict the timing of a bowel movement so that caregivers can ensure the individual is sitting on the toilet when one takes place and then reinforce continence. Thus, a multidisciplinary approach incorporating both medical and behavioral approaches is necessary in the treatment of encopresis in individuals with ASD.

This is an 8-week, randomized clinical trial of 112 children, ages 5 to 12 years, 11 months with ASD and encopresis. Participants will be randomized to receive either two weeks of MIE or one week of TAU. The study initially had a third study arm of one week of MIE treatment, which was discontinued in October of 2019.