Preoperative investigations included in most of the studies a colonic transit studies, barium enema, colonoscopy, study of anorectal physiology, and defecography. All the preoperative assessments for each study are reported in Table 14.2.

Psychological evaluation has shown to be a significant predictive method for the selection of patients with constipation suitable for SNS treatment, reaching a success rate of 85 % [34].

Using MMPI, Wexner and colleagues found in constipated patients a significant elevation on the hypochondriasis and depression scales [40]. They concluded that constipated patients may benefit greatly by adding a psychological component to the treatment regime.

Another study carried out in 40 patients with ODS who underwent transanal rectal prolapsectomy, a recurrence of constipation occurred in 52 % of cases at a median follow-up of 3 years [41]. This decreased to 20 % when patients with psychoneurotic disorders were excluded, suggesting that the underestimated occult-associated disease, such as anxiety and depression, might be associated with a poor result.

In the study proposed by Carriero et al. [34], the essential role of psychological evaluation was confirmed when the results of the group of patients who were initially excluded due to their psychological conditions were added, causing a significant drop of the success rate and making it comparable to the lowest success rates reported in literature.

In another study, Martellucci and Naldini [42], performing a retrospective analysis of patients with STC with pathologic colonic transit time that underwent SNM test, evaluated the success of the treatment related to the preoperative bowel preparation protocols.

In their study, 20 patients underwent no preparation, 7 patients underwent to a preoperative enema, and 11 patients underwent to a complete preparation with sodium phosphate. Twenty-five patients (65 %) were definitively implanted: 12/20 (55 %) patients in the first group, 4/7 (57 %) in the second group, and 9/11 (82 %) in the third group underwent to definitive SNM, respectively, suggesting that preoperative bowel preparation could help to improve the results during the screening period of SNM for STC.

General results are included in Table 14.3.

In the Malouf and Kenefick patients [18, 19], four of the ten tested patients demonstrated a successful increase of symptoms and where definitively implanted. An increase in the number of spontaneous defecations was demonstrated at 6-month follow-up. Improvement in the Cleveland Clinic constipation score was reported. Ganio et al. [32] described 40 patients with functional anorectal and urinary disturbances, of whom 12 had constipation. After 10 days of peripheral nerve evaluation (PNE), ten completed the course of stimulation. This group showed an improvement in initiating evacuation and a reduction of time required to evacuate. In the Naldini et al. [35] study, 15 patients with slow-transit constipation underwent temporary SNS. Of these, nine managed to have permanent implant. At 6 months, there was an increase in the number of bowel movements per week. In the Holzer et al. [33] prospective study, 19 patients underwent to temporary SNS. Eight of these had slow-transit constipation, and nine had evacuatory dysfunction. Eight patients (four with slow-transit and four with evacuatory dysfunction) undergone to permanent stimulation and it results in a reduction of Cleveland Clinic constipation scores and short form 36 (SF-36) quality of life (QoL) scores. Kamm et al. [21] in 2010 performed a multicenter prospective study with 62 patients underwent test stimulation of whom 45 (73%) progressed to permanent stimulation with a follow-up median of 28 months. Thirty-nine (87 %) of the 45 who had undergone permanent stimulation showed an improvement in frequency of defecation, straining, sensation of incomplete evacuation, abdominal pain, and bloating. There was an improvement of the Cleveland Clinic constipation score from 18 at baseline to 10. The colonic transit time in half of the patients with slow gut transit had normalized by 6 months. Govaert et al. [38] reviewed 117 patients who had undergone temporary test for SNS. Of these 68 proceeded to permanent SNS. Some of the patients in this report were part of the multicenter study published by Kamm et al. [21]. There was an initial significant improvement in the Cleveland Clinic constipation score from mean 17 to 10,2 at first follow-up, maintained at a 37 months. Sharma et al. [36] submitted 21 patients to temporary stimulation, 18 of whom had slow-transit constipation. Of these, 11 went on to have a permanent implant. Eight of these 11 patients stopped using laxatives. Carriero et al. [34] proposed a psychological assessment for the selection of patients. In this study, 68 patients with slow-transit constipation underwent Minnesota Multiphasic Personality Inventory (MMPI)-2 questionnaire, but only 45 completed the questionnaire. Thirteen had a normal score and underwent temporary screening phase. Of these, 11 proceeded to permanent stimulation. Interestingly, nine of the patients who had refused to complete the MMPI-2 questionnaire, or had an abnormal score, requested to be with tested despite the psychological evaluation results. Of these, only three (33 %) progressed to permanent stimulation.

In the prospective randomized double-blind placebo-controlled crossover trial of Knowels et al. [26], 14 female patients with proctographically defined evacuatory dysfunction (ED) and demonstrable rectal hyposensitivity were studied. In this study, 13 patients completed the trial, and 11 were definitively implanted. Defecatory desire volumes to rectal balloon distension were normalized in 10 patients and maximum tolerable volume in 9. There was a significant increase in the number of successful bowel movements per week and in the Cleveland Clinic constipation score. It has to be shown that after a follow-up of 19 months, only 9 patients still benefit from the treatment, partially influencing the good success rate.