We feel that obtaining a detailed history and physical exam is usually the most important determinant that influences the decision making [2, 3]. Therefore when considering a diagnostic test, the key question is whether this test will affect the overall management plan.

Some studies reported that physiologic testing could guide the physician in treating patients with FI. Vaizey and Kamm prospectively studied 100 patients to evaluate the impact of anorectal investigations (this included anal ultrasound) on the management decisions. They found that the information provided by anorectal physiologic assessment had an impact on management in patients with benign anorectal disorders. However, carefully evaluating their study, even though anorectal assessment had an important diagnostic and prognostic role in managing patients with benign anorectal disorders, endoanal ultrasound was actually the driving test that changed their plans in FI patients (n = 51); anorectal physiology helped guide decision making for patients with constipation [4]. Therefore, anorectal physiology testing did not really seem to influence FI decisions.

Wexner and Jorge conducted a prospective study on 308 patients presenting with various complaints (constipation, fecal incontinence and chronic intractable rectal pain) to assess the usefulness of colorectal physiological studies to identify all relevant causes that could be treated [5]. Out of 308 patients, 80 presented with FI. The etiology of FI was revealed by history and physical examination alone in 9 patients (11 %) and by physiological testing (anal manometry, cinedefaecography, anal electromyography and pudendal nerve terminal motor latency PNTML) in 44 (55 %). The etiology remained undiagnosed in 27 patients (34 %) even after testing. The causes of FI were loss of muscle fibers (26 %), neuropathy (13 %), combined muscle loss and neuropathy (19 %), and rectoanal intussusception (9 %). They concluded that physical examination might detect anorectal scarring, attenuation of the rectovaginal septum/anal sphincters, and poor contraction of the sphincter; however clinical evaluation cannot confirm the presence of iatrogenic injury. Physical examination also was not capable of detecting pudendal neuropathy. In their view, findings of colorectal physiological testing permit assignment of patients to treatment regimens. It is important to note that this study also included more investigations than just anal physiology and they reported using all this data when making their conclusion. Therefore the role of anal physiology could not be determined.

On the other hand, more recent studies reported no benefit to physiologic testing for FI. Lam et al. [3] prospectively assessed 600 patients referred for anorectal testing and compared those with and without FI (48 % with fecal incontinence and 87 % female) in order to formulate a statistical model to determine which factors would predict FI, particularly after a stoma closure. In regards to anorectal physiology testing, women with FI had lower anal pressures, shorter sphincter length, and smaller rectal capacity. Men with FI had lower anal pressures. Incontinent and continent patients had a broad overlap in anorectal physiology testing. They did find that all patients with a rectal capacity <60 cc had FI and of those with maximum basal and squeeze pressures ≤20 mmHg, only 4 % were continent. They used six items to create a statistical model for FI (female, age, stool consistency, maximum rest and squeeze pressures, rectal capacity, and anal sphincter defects). They then used this model on 5 women to accurately predict the risk of FI following stoma closure. While this study did demonstrate some utility for anal physiology testing, this was used in combination with other tests and consideration of patient characteristics.

Similar findings were also reported by Raza and Bielefeldt [6]. They reviewed 298 patients who had anorectal manometry mainly for FI (51 %) and constipation (42 %). Patients with fecal incontinence had significantly lower pressures compared to individuals with constipation, but the data overlapped significantly. The sensitivity of resting and squeeze pressures were 50 and 59 %, respectively while the specificity for low squeeze pressures was only 69 %. They concluded that manometry should not be used routinely because it has poor discriminatory power.

Zutshi et al. conducted a retrospective study on 53 women who had a sphincter repair. They reported that anal manometry did not correlate with severity of incontinence nor did it assess or predict response to treatment [1]. Bordeianou et al. looked at the relationship between anorectal manometry, fecal incontinence severity (FISI scores), and findings at endoanal ultrasound in 351 women [7]. They found FISI scores were equally severe in patients with or without a sphincter defect; a weak correlation was observed between resting anal pressure and the severity of defects on anal ultrasound; and no correlation existed between maximum squeeze pressure and FISI scores. In the subset of patients with a sphincter defect (n = 148), a weak and negative correlation was reported between the mean resting pressures and maximum resting pressures, the size of the internal and external sphincter defects, as well as the size of the perineal body.

In a Cochrane review evaluating the effects of sacral nerve stimulation (SNS) for FI and constipation, anorectal manometry did not appear to predict which patients would benefit from SNS and the authors concluded that testing with anorectal manometry did not appear to provide clinically useful information [8].

Anal manometry has many limitations. One drawback is that it is very difficult to compare results between institutions because manometric findings are not standardized; the normal range of values varies at each institution [9]. There are no normal values stratified by sex and age [10] and different companies manufacture different types of machines that also adds to the variability.

Intact pudendal nerves may contribute to the success of FI treatment such as SNS or sphincter repair. However PNTML reflects the activity of the fastest fibers, which makes it a poor indicator of damage to the entire range of nerves that supply the sphincter complex. Additionally it is operator dependent. This has led many investigators to no longer recommended PNTML when evaluating FI [11–13]. In a systematic review by Glasgow and Lowry, 900 patients from 16 studies (2 case control, 1 prospective and 13 retrospective studies) were included as they looked at the outcomes of anal sphincter repair for FI [14]. In five studies, pudendal neuropathy, resting and squeeze anal pressures, anal canal length, and rectal compliance did not predict long-term outcomes following sphincteroplasty [15–19]. However, there was one retrospective study that reported pudendal neuropathy predicted the outcome after sphincter repair for FI [20].