Digital rectal examination of sphincter pressures in chronic anal fissure is unreliable

PURPOSE: Chronic anal fissure is said to be associated with internal sphincter hypertonia. However, an unknown proportion of fissures may be associated with normal or even low resting pressures and may subsequently be resistant to pharmacological treatments or at risk from surgical treatments, both of which aim to reduce sphincter hypertonia. This study investigated the ability of surgeons to detect low or normal pressure fissures by digital rectal examination. METHODS: Patients with chronic anal fissure were assessed prospectively. The results of anal manometry performed on these patients were compared with digital rectal assessment of sphincter tone undertaken by a surgeon blinded to the manometry results. RESULTS: Forty consecutive patients (21 male) with chronic,trial fissure were studied. Twenty-two (55 percent) had normal maximum resting pressure and a further 3 (8 percent) had low pressures on anal manometry. On clinical assessment, only five (13 percent) patients were evaluated as having no anal hypertonia. Clinical assessment of anal tone correctly identified 14 of 15 patients with high manometric maximum testing pressure (sensitivity, 93 percent), yet detected only 4 of 25 patients with normal or low pressures (specificity, 16 percent). The positive predictive value of clinical assessment of anal tone was 40 percent and the negative predictive value, 80 percent. CONCLUSIONS: The incidence of patients with chronic anal fissure without high manometric maximum resting pressure is higher than previously reported. The ability of surgeons to identify this group clinically was poor. It is reasonable to treat all patients primarily medically, and then selectively investigate by manometry those patients who fail medical therapy before considering lateral sphincterotomy.