Can digital examination substitute anorectal manometry for the evaluation of anal canal pressures?

Anorectal manometry provides objective information on the sphincter function of the anal canal. However, in many centers sphincter function is evaluated by digital examination, due to the unavailability of manometry.

A study is made to correlate the sensitivity and specificity of a quantitative digital examination in the analysis of sphincter tone with the pressures recorded by manometry, and to examine the capacity of both techniques to discriminate continent subjects and incontinent patients.

A total of 191 patients were divided into three groups: control (C), obstructive defecation (OD) and fecal incontinence (FI). Subjective quantitative digital evaluation of anal tone was performed on a scale of 0 to 5 points at rest, and 0 to 10 points at squeeze. A correlation analysis was performed, and the sensitivity and specificity of each fecal incontinence diagnostic test was determined.

Digital examination found rectal tone to be diminished in elderly patients. A significant correlation was established between the digital and manometric tone readings, both at rest and at squeeze. Both techniques showed a low anal sphincter pressure in the FI group versus the C and OD groups. Differences in tone were recorded between the C and OD groups with manometry, but not with digital examination. The latter was in turn found to be more sensitive but less specific than manometry in differentiating between fecal continence and incontinence.

Although digital examination does not substitute anorectal manometry, a good correlation exists between the two techniques. In this sense, digital examination may afford an approximate clinical evaluation of some fecal continence mechanisms in those centers where manometry is not available.