4 Comparing anorectal function tests 111 using similar instructions to patients.16 Even a small difference in outcome could lead in a different interpretation. It must be noted that in contrast to most ARM studies we used the 3D probe. DRE correlated better with 3D-HRAM in patients referred for fecal incontinence. With 54% this was the largest group in this study. However, defining ‘normal’ resting and squeeze pressures for ARM values is quite difficult. There is obviously an overlap since several studies showed different values for normal and abnormal resting and squeeze pressures for ARM.14,23-28 To be accurate in comparing between groups, the pressures should be adjusted according to age, gender, and parous and nulliparous females. But these differences were small and to make comparisons between tests manageable in this study we did not differentiate. The surgeons’ DRE and the pelvic floor physical therapist’s DRE were compared to the s-EMG and showed some discrepancies. The surgeon’s DRE and the pelvic floor physical therapist’s DRE were categorized as ‘low’ whereas the s-EMG categorized ‘high’ in three and four patients, respectively. However, one patient was categorized ‘high’ with DRE and ‘low’ with s-EMG. This can probably be explained by the fact that patients who can hardly control their external anal sphincter might overcompensate with their levator muscle. As we measured with s-EMG, the mean of the total electrical activity of the external anal sphincter including the levator muscle, the EMG activity might be higher than expected. When retrospectively assessing the 3D-HRAM, these patients showed indeed higher pressures of the posterior levator muscle on the 3D image in contrast to the sphincter and vice versa for the patient with a chronic anal fissure. Furthermore, high tone on the levator muscle with DRE might be turgor which is not measured with s-EMG. For this reason, comparing s-EMG with other tests might not be appropriate and should probably be used only to confirm physical examination and biofeedback registration. The correlation between s-EMG and the 3D-HRAM was better for squeeze pressures and electric activity than resting pressures and electric activity with an agreement of 59% and 37% respectively. A study from 1989 also showed limited concordance with a correlation coefficient of 0.55 (p<0.001) between the maximum squeeze pressure with ARM and maximum contraction pattern with de EMG.17 Regarding diagnosing dyssynergia while straining with s-EMG and 3D-HRAM, our results were not in line with the results by Chiarioni et al.30 In our study, s-EMG and ARM were concordant in 52% while Chiarioni et al. described an agreement of 88% for classifying patients’ dyssynergic or not dyssynergic. Both tests are used to test the anorectal function but
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