Treatment of Gastrointestinal Sphincters Spasms with Botulinum Toxin A

Botulinum toxin A inhibits neuromuscular transmission. It has become a drug with many indications. The range of clinical applications has grown to encompass several neurological and non-neurological conditions. One of the most recent achievements in the field is the observation that botulinum toxin A provides benefit in diseases of the gastrointestinal tract. Although toxin blocks cholinergic nerve endings in the autonomic nervous system, it has also been shown that it does not block non-adrenergic non-cholinergic responses mediated by nitric oxide. This has promoted further interest in using botulinum toxin A as a treatment for overactive smooth muscles and sphincters. The introduction of this therapy has made the treatment of several clinical conditions easier, in the outpatient setting, at a lower cost and without permanent complications. This review presents current data on the use of botulinum toxin A in the treatment of pathological conditions of the gastrointestinal tract.


Introduction
Although the therapeutic potential of botulinum toxin (BT) for skeletal muscle disorders was first realized in the 1970s [1], it was not until nearly two decades later that it was also shown to be effective in the gastrointestinal tract (GIT) [2][3][4][5]. Since then, however, there has been a rapid increase in the number of reports in a variety of GIT conditions characterized by dysfunctional smooth muscle [5,6]. This article will review the BT efficacy in the treatment of these conditions. In particular, we have taken into account all applications at all level of the GIT. We have reported the latest findings of the literature on the BT use in the treatment of GIT diseases. We believe that the introduction of BT injection in the treatment of these patients represents an innovation equal to the introduction of laparoscopy. The introduction of this therapy has made the treatment of several clinical conditions easier, in the outpatient setting, at a lower cost and without permanent complications.

Background
Normal GIT motility depends on intrinsic neurons contained in the enteric nervous system (ENS), with significant modulatory input being provided by the central nervous system (CNS) via autonomic sympathetic and parasympathetic nerves [7,8]. Immediate control of muscle tone in the gut reflects a balance between both excitatory (predominantly cholinergic) and inhibitory (predominantly nitrinergic). In some disease states, this balance is disrupted, usually due to a relatively selective loss of inhibitory neurons [9][10][11]. In this setting, BT, by blocking excitatory neurotransmitter release, can restore the balance and cause a decrease in the resting tone of the muscle involved.
Although BT can clearly inhibit the release of acetylcholine, little else is known about its effects in GIT muscle. Thus, while nitric oxide (NO) release is not affected-which is to be expected, since this is not a vesicular process-the specific effects on other potentially important neurotransmitters has not been well documented [12,13]. Further, there is some suggestion that it may also inhibit the responsiveness of smooth muscle to exogenous stimuli, an effect that is quite unique to the GIT.
GIT smooth muscle has an inherent motility and coordinated, aimed at the progression of ingested food from the oropharynx to the anal canal. The different regions of the gastrointestinal tract motility own and have a characteristic, capable, however, each play a specific role. The term includes motility, in fact, a number of events summarized as follows: 1. Ability of smooth muscle cells to contract (myogenic event); 2. Coordination of the contraction of smooth muscles, nerves through intrinsic and extrinsic (neurogenic event); 3. Coordinated muscle contraction, with subsequent increase of the intraluminal pressure; 4. Propulsion of content, which is the final event with the participation of the above. All these functions are under the direct control of the so-called ENS. It consists of all the neurons of the gastrointestinal tract and shows an independent function of the central nervous system, so as to merit the label "brain of the gut".
A deficiency of enteric neurons causes obstruction and lack of intestinal propulsion [14]. The ENS is composed of two main ganglionated plexuses (Auerbach's myenteric plexus and Meissner's sub-mucous plexus) and non-ganglionated plexuses (the longitudinal muscle plexus, the circular muscle plexus, the plexus of the muscularis mucosae, and the mucosal plexus) [8]. Intraparietal neurons encompass motor excitatory and inhibitory neurons, interneurons and intrinsic sensory neurons. Sympathetic and parasympathetic neurons also innervate the GIT. The primary excitatory transmitter is ACh, while inhibitory transmitters are NO, adenosine triphosphate (ATP), and VIP [8].
At the cellular level, smooth muscle contraction and relaxation are regulated by changes in cytosol calcium levels [15]. These functions depend on the intrinsic electrical and mechanical properties of GIT smooth muscles and are regulated by the ENS and by sympathetic and parasympathetic influences [8]. Hormones also influence GIT motility [16]. Interstitial cells of Cajal act as local pacemakers to generate the rhythmic activity of the circular muscle layer throughout the GIT. Motor neurons control the musculature indirectly, through their action on Cajal's cells. Substances, such as histamine, serotonin, adenosine, and eicosanoids, produced by non-neural cells, can influence smooth muscle activity [17].

Cricopharyngeal Dysphagia
Dysphagia associated with cricopharingeal (CP) muscle dysfunction has a significant impact on overall patient quality of life [18]. CP dysphagia, either idiopathic or secondary to various neurologic or muscular conditions, is characterized by incomplete or poorly coordinated opening of the upper esophageal sphincter (UES) during swallowing. This proximal dysphagia can result in laryngeal penetration or tracheal aspiration of swallowed food. The CP muscle is therefore often a target of surgical interventions for dysphagia, including bougie or balloon dilatation, myotomy and chemodenervation by treatment with BT [18][19][20][21][22][23]. UES dilation is often effective and of low risk, but also has a short clinical effect. Transcervical CP myotomy is effective in treating CP dysphagia, but has significant risk of infection, salivary fistula formation, and recurrent laryngeal nerve injury [24]. Endoscopic laser CP myotomy was described in the early 1990s, with evidence of successful treatment in multiple patient series. CP myotomy improves UES opening, but will not alter pharyngeal muscle contractile forces, and therefore may not benefit every patient with CP dysphagia. Traditionally, CP myotomy has been the mainstay of treatment but other options such as dilation and BT injection have been used with good results [18,23]. BT injection into the CP muscle to treat dysphagia was first described in 1994 by Schneider and co-workers, [25] in a series of 7 patients, as an alternative treatment to the more invasive myotomy procedures.
A number of injection techniques have been employed including rigid endoscopy with electromyographic control, flexible endoscopy, and an open technique with various doses (10-50 units). Endoscopically, 3 to 4 injections of BT can be delivered to the dorsomedial and bilateral ventromedial compartments of CP muscle. Furthermore, the location of the CP muscle has been verified by EMG in a number of studies especially in the otolaryngology literature.
CP injection of BT has distinct appeal in patients who are not ideal candidates for longer general anesthesia or in whom the temporary nature of BT injection is warranted. It may be advantageous to pursue CP injection of BT in patients in whom multilevel dysphagia is suspected and in whom the clinician suspects that there may be some detriment to treatment directed at the UES. Additionally, CP injection of BT is a diagnostic tools used by clinicians to identify patients who may potentially benefit from CP myotomy [18,20,21,26]. A review of the literature identified 20 studies that focused on the use of CP injection of BT (Table 1). Only two series were of more than 20 patients; the largest study included 34 patients. The causes of CP dysfunction in these published series encompassed several diagnosis, including neurological diseases, diabetic neuropathy, external-beam radiation treatment, cerebrovascular accident, and others. The dosage and administration techniques of BT were also quite variable [18]. There were also different types of BT administered: Dysport (Ipsen, Paris, France) and Botox (Allergan, Irvine, USA); the Dysport doses delivered to CP muscle ranged from 60 to 180 units, and the Botox doses ranged from 4 to 120 units [18,39].
In general, the majority of patients reported improved swallowing function: approximately 75% in combined analysis. Complications were infrequent and included transient vocal fold paresis, temporary worsening of dysphagia, neck cellulitis, and aspiration pneumonia. There were no reported deaths in the literature that were directly related to CP injection of BT. Recently, Kelly and coworkers demonstrated that CP injection of BT is a well-tolerated treatment for dysphagia related to CP dysfunction, with good efficacy in the majority of their 49 patients [18]. On the basis of these results, CP injection of BT appears to be effective in patients with UES dysfunction. Response to BT injection may select out a group of patients with higher likelihood of a more durable response to surgical myotomy [40]. Further work, however, is needed to define the population of patients who might have a poor response to BT treatment. Furthermore, non-response may indicate another etiology of dysphagia, i.e., stricture.

Crycopharingeal Achalasia (CPA) in Children
The condition is characterized by an incomplete relaxation or by a lack of coordination of the UES [22,41]. CPA is a different entity then the CP dysphagia that was see in adults. The exact cause of CPA is unknown. Immaturity of the interstitial cells of Cajal may explain why there have been reports of spontaneous resolution of CPA seen in infants [42]. CPA has also associated with gastro-esophageal reflux disease and CNS abnormalities [21,22,[41][42][43][44].
Recently, six children were identified with CPA [22]. The decision to proceed with BT therapy was based on ongoing severe symptoms, the necessity of altered feeds, and parent preference over a surgical myotomy. The number of injections ranged from 1 to 3 per patients. The mean dose was 5.6 units/kg, with a range of 1.6 units/kg to 7.9 units/kg and a median of 6.0 units/kg. In those patients with multiple injections, the mean time between injections was approximately 13 months. The mean time to return to normal radiographic swallow study was 8.2 weeks. Two of the children benefited from BT injections and went on to have CP myotomy, while four of the children did not require myotomy and their symptoms resolved after one or two injections. The authors concluded that BT injection of CP muscle is a useful tool to help diagnose and treat CPA [22]. It is a feasible alternative to more invasive surgical procedures. However, more research is needed to elucidate the optimal dosing, frequency of injections, and when to move on to surgical intervention.

Achalasia
The major pathophysiological lesion in achalasia, which means failure to relax, results from a relatively specific loss of nitrergic inhibitory neurons of the LES, resulting in an inability of the sphincter to relax after swallowing [45]. This results in a functional obstruction and dysphagia. Although no cure exists for achalasia, there are a number of palliative treatments available including surgical myotomy, pneumatic dilation (PD), and BT injections into the LES [46][47][48][49][50][51]. Surgical myotomy has proven durable, but is associated with increased morbidity and mortality in high-risk surgical patients. Pneumatic dilation of the sphincter results in an initial symptomatic improvement in 60%-90% of patients but repeated dilations are often necessary. Furthermore, the procedure carries a small but significant risk of esophageal perforation [52][53][54]. Thus, BT provides a potentially attractive alternative to the above treatment methods [49].
Endoscopic injection of 25 units of BT in 4 LES quadrants is generally the standard of care. The efficacy of BT in achalasia has been proven by the results of several randomized trials comparing it to either placebo or pneumatic dilation. Table 2 summarizes the response rates to BT in patients with achalasia.
In general, 75%-100% of patients show an initial response but more sustained improvement (beyond 6 months) is seen in about two-thirds. For unclear reasons, it appears that patients older than 50 years of age respond at a higher rate (82% vs. 43% in younger patients). Similarly, patients with so-called vigorous achalasia (with the esophagus retaining some contractile ability) respond at a higher rate (100% vs. 52% with classic achalasia). The two treatment had equal initial success rate (dilatation 83%, BT 75%).
In the long term the efficacy of BT injection was statistically significantly and shorter than that of balloon dilatation Greaves et al.,

[63] BT 11
The relapse rate was 73% within 2 years from treatment. There were a beneficial effect on dysphagia, no improvement in chest pain or regurgitation scores, and no reduction of mean LES pressure were improved at 6 weeks   BT + PBD vs.

PBD 91
The mean duration of follow-up was 48 months (12-96 months). 41 of 51 patients were followed up more than 2 years. Effect of therapy lasted in 75% (31/41) of them. The cumulative 5 years remission rate in combined treated patients was higher than in controls bu not statistically significant. (p = 0.07).
Injection of BT followed by PD seems to be effective for long-term result but the combined therapy is not significantly superior to PD alone Several studies have compared BT to pneumatic dilation with most reporting similar initial clinical or manometric responses. However, the one-year remission rate after a single injection is markedly inferior for BT, which is to be expected given its pharmacological properties. In the only study comparing the two modalities in a head to head comparison, 80 patients were randomized to receive 100 BT units or laparoscopic surgical myotomy with fundoplication. After six months, symptom scores improved more in surgical patients (82% vs. 66%, p < 0.05). The drop in LES pressure was similar in the two groups; the reduction in esophageal diameter was greater after surgery (19% vs. 5%, p < 0.05). The only complication in the surgical group was one patient bled at the trocar site. The probability of being symptom-free at two years was 87.5% after surgery and 34% after BT (p < 0.05). The same group investigated the cost effectiveness of the two modalities and concluded that BT was more cost effective in the short term, but at two years, cost between the two groups was similar. The results of a recent meta-analysis suggest that PD is the more effective endoscopic treatment in the long-term (greater than 6 months) for patients with achalasia [52].
BT injections into the upper GIT appear to be quite safe with very few, if any, reports of serious adverse effects. The incidence of gastro-esophageal reflux has not been well characterized in most studies but has been reported to be about 20%, by symptoms at least. There has also been some question in recent years whether BT prior to PD or myotomy complicates the more invasive procedures possible secondary to LES fibrosis. However, although previous BT injection (or PD for that matter) may make myotomy more challenging technically because of obliteration of tissue planes, this does not appear to affect the final outcome after myotomy.

Other Esophageal Disorders
BT has also been used in a variety of less well characterized esophageal conditions including diffuse esophageal spasm (DES) and patients with non-cardiac chest pain suspected to be on the basis of a dysfunctional esophagus. DES is a condition that is related to achalasia and may be associated with LES dysfunction as well [89][90][91][92][93][94][95][96]. The largest clinical trial assessing the effect of BT in DES patients evaluated 9 patients [97,98]. A significant reduction in symptom score was noted at week 4 and 8. A recent study examined 22 patients with DES or nutcracker esophagus who had primarily dysphagia and gave them blinded saline or BT injections in a crossover study design [94]. Results showed that symptoms scores and weight loss improved after BT treatment, not the saline injections, and this benefit was sustained for over a year in almost half of the patients. Unfortunately, there have been no other clinical trials evaluating BT as a treatment option for this disorder.
In addition to dysphagia and regurgitation, chest pain can be associated with achalasia, DES, ineffective esophageal motility (IEM), and isolated LES dysfunction which may respond to BT administration as shown in previous studies. A study, with improvement of chest pain as the primary end-point, evaluated 29 patients with non-cardiac chest pain who received 100 BT units injection into the LES, same as the treatment regimen for achalasia. Seventy-two percent of the patients responded with at least 50% reduction in chest pain [99].
Similar to idiopathic achalasia, in Chagas' disease (CD), a common disease in South America [73,[100][101][102][103][104], slow esophageal emptying is due to nonrelaxation of the LES. Only one representative series on 24 patients has been published regarding BT in esophageal CD. The authors have been showed that 58% of the patients had clinical improvement of dysphagia at 6 months follow up. Interestingly, gender, age and LES pressure did not influence outcomes, contrary to the results obtained in idiopathic achalasia series [57,73].

Gastroparesis
Gastroparesis or delayed gastric emptying resulting in nausea, vomiting, dyspepsia, and abdominal bloating is a common problem in patients seen by primary care physicians and gastroenterologists. Gastroparesis can occur as a result of poorly controlled diabetes mellitus, post-surgical manifestations, or idiopathic causes [105][106][107][108]. In recent years, BT injection into the pylorus has been investigated as a treatment option in this otherwise debilitating disorder.
The initial study evaluating the BT efficacy in patients with diabetic gastroparesis assessed six patients with abnormal solid phase gastric emptying studies [109]. Each patient received 100 BT units into the pyloric sphincter and symptom scores and gastric emptying were assessed after six weeks. There was an improvement of subjective symptom scores of 55%, which was maintained at six weeks. In addition, there was a 52% improvement in gastric emptying at six weeks. Another study investigated the BT use in cases of idiopathic gastroparesis [110]. Ten patients were given 80-100 BT units and a 38% reduction in symptom scores were seen at 4 weeks which correlated with findings of increased gastric emptying. A recent study evaluated the effects of BT on diabetic gastroparesis for 12 weeks [105]. Eight patients received 200 BT units into the pyloric sphincter, and seven patients completed the 12-week follow-up. Mean symptom scores declined from 27 to 12.1 (p < 0.01). Furthermore, six of the seven patients gained weight (p = 0.05) and gastric emptying scan time improved in four patients [105]. The largest study to address this issue retrospectively evaluated 63 patients who met the study criteria [108]. Gastroparesis was secondary to diabetes in 26 patients (41.2%), after surgery in two (3.2%), and idiopathic in 35 (55.6%). Twenty-seven of 63 (43%) patients experienced a symptomatic response to treatment (100 to 200 units) with a mean duration of five months. Male gender was associated with response to therapy. However, vomiting as a major symptom was predictive of no response to BT [108]. Further studies were needed to address these issues and to better define potentially responsive patients [111][112][113][114][115].

Obesity
BT injection into the gastric antrum may be used to transiently decrease gastric emptying as a treatment for obesity [116][117][118][119][120]. Preliminary data in rats have shown a significant loss of body weight associated with a reduction of dietary intake in the BT treated group. In a double blind controlled study, 24 morbidly obese patients (mean body mass index (BMI) 43.6 ± 1.09 kg/m 2 ) were blindly randomized to receive 200 BT units or placebo into the antrum and fundus of the stomach by intraparietal endoscopic administration [121]. The two groups were homogenous for anthropometric characteristics. Eight weeks after the treatment, BT patients had significantly higher weight loss (11 ± 1.09 kg vs. 5.7 ± 1.1 kg, p < 0.001) and BMI reduction (4 ± 0.36 kg/m 2 vs. 2 ± 0.58 kg/m 2 , p < 0.001) than controls. No significant side effects or neurophysiologic changes were found. Similar results have been found in an open label study of 10 obese adults (BMI 31-54 kg/m 2 ) who received 100 units (4 patients) or 300 units (6 patients) of BT and were followed for 16 weeks [122].
Further results demonstrated that BT makes weight loss easier in obese patients [123]. It seems conceivable that BT acts by increasing the solid gastric emptying time and reducing the solid eating capacity of the stomach. However, the results in literature are controversial. In several clinical experiences, intragastric BT injection does not seems to reduce body weight [118,[124][125][126].

Others Gastropyloric Disorders
BT has been used to facilitate gastric emptying in patients who underwent pylorus-preserving duodenopancreatectomy [127]. Initial studies suggests that BT injection into the pylorus improves both gastric emptying and symptoms.
Infantile hypertrophic pyloric stenosis is a congenital hereditary disorder characterized by a functional gastric outlet obstruction [128]. Obstruction is the result of a gradual hypertrophy of the circular smooth muscle of the pylorus, and the neurons that innervate the circular-muscle layer lack NO synthase. Recently it has been observed lack of response to BT injection in two patients with pyloric stenosis. Studies have shown that BT injection helps patients suffering from post-surgical pyloric clogging. BT injection is also used as an alternative method for the treatment of gastric emptying disorders [129][130][131]. In a recent study, the authors compared the effect of BT injection and pyloroplasty in preventing delayed gastric emptying after esophagectomy for esophageal cancer [115]. Sixty patients were included in the study: These patients were randomly divided into two groups. In group A, 30 patients underwent pyloroplasty, and in group B injection of 200 BT units into the pyloric sphincter muscle was used in 30 patients. An isotope-scan three weeks after surgery showed that five patients in group A and three in group B had delayed gastric emptying; there was no significant difference between the two groups, and the success rate of BT injection was 90% [115]. BT injection may be used instead of pyloroplasty as a simple, effective and complication-free method to prevent gastric emptying delay.

Sphincter of Oddi Dysfunction (SOD)
The sphincter of Oddi is a small ring of muscle that surrounds the biliary and pancreatic ducts just before they open into the duodenum. SOD is a poorly understood and controversial condition postulated to result in biliary pain, typically in the setting of a previous cholecystectomy. It has also been hypothesized that pancreatic SOD can result in pancreatic type pain and/or recurrent pancreatitis. The standard of SOD treatment currently is endoscopic sphincterotomy, which is a relatively high-risk procedure that is not uniformly effective. Hence there is interest in the use of a simpler procedure such as BT to serve as a therapeutic trial patients who respond to this treatment could then go on for more permanent relief using a sphincterotomy [132][133][134]. This was first suggested in a short report on two patients. Subsequently a larger study was reported evaluating twenty-two patients who had undergone cholecystectomy and had manometrically confirmed type III SOD [135]. Six weeks after 100 BT units injected into the sphincter, 12 patients (55%) were symptom-free, but ten patients (45%) were not. Of the ten patients who did not experience symptomatic benefit from BT injection, five had normal basal sphincter of Oddi pressures (<40 mmHg), and biliary sphincterotomy did not relieve the symptoms of these patients. Two of the remaining five patients with sustained sphincter hypertension after BT injection benefited from biliary sphincterotomy. Of the 12 patients who initially responded to BT injection, 11 patients remained symptom free for a median duration of six months. These patients had recurrence of biliary hypertension and responded to biliary sphincterotomy. The authors concluded that response to BT injection may select a subset of patients who will respond to biliary sphincterotomy.
BT has also been used with similar intent, although in an uncontrolled manner in patients with acute recurrent pancreatitis suspected to be due to pancreatic SOD [136].
The future role of BT injection in SOD still needs further investigation but current literature supports its use as a therapeutic trial in patients with SOD.

Others Biliary Disorders
BT induced relaxation of the sphincter of Oddi may help to treat patients with acalculous biliary pain [137]. A total of 11 patients had a positive response to BT injection of 100 UI into the sphincter of Oddi. Endoscopic biliary sphincterotomy has been induced a relief of biliary pain in 10 of these cases [137,138].
BT injection is as effective as endoscopic biliary stent placement in resolving cystic duct leaks in a canine model [139].

Pelvic Floor Dyssenergia
Pelvic floor dyssenergia, also known as anismus, is a common cause of chronic constipation, hallmarked by inappropriate, paradoxical contraction or a failed relaxation of the puborectal muscle and EAS during defecation [2,3,140]. In normal patients, the puborectalis muscle and the EAS relax to straighten the anorectal angle and open the anal canal. Usually, this alteration in defecation is from maladaptive learning and responds to biofeedback in 60%-70% of patients as demonstrated in mostly single group, uncontrolled trials. Surgery has not been shown to be effective and has been largely discouraged as a treatment option. There are a limited number of studies evaluating the BT use in pelvic floor dyssenergia (Table 3).     An initial trial evaluating seven patients with constipation and anismus received BT of unknown dose into the EAS [141]. Symptom scores improved significantly correlating with a reduction in the maximum voluntary and anal canal squeeze pressure and a significant increase in the anorectal angle on straining with subsequent fecal incontinence in two patients. In another study, with a sample size of 4 patients with anismus, the dose of BT ranged from 6 to 15 units injected into the EAS or puborectalis muscle under electromyography guidance [144]. All four patients, who had numerous failed biofeedback sessions, responded to BT with two patients having sustained responses for up to one year. A larger study evaluating 15 patients at a dose of 25 BT units injected into the EAS showed improvement in 13 patients (87%) for a mean of 4.8 months [143]. It is unclear whether BT should be injected into the EAS or the puborectalis muscle. Another study evaluated twenty-five patients who received 10 BT units on each side of the puborectalis muscle or 20 units in the posterior aspect of the muscle. Manometric relaxation was achieved after the first injection in 18 patients (75%), which endured throughout a six-month follow-up. Seven of 16 patients who failed the first injection had an additional one. Symptom improvement of 29.2% in straining index was recorded during follow-up with an overall satisfaction rate of 58.3%. Similar results have been noted in patients with Parkinson's disease [149,159].
Rectoceles are commonly associated with outlet obstruction, such as pelvic floor dyssenergia. Therefore, decreasing anal sphincter tone during strain may decrease the size of the rectocele and improve symptoms of constipation. In a study of fourteen patients with anterior rectocele, each patient received 30 BT units at three sites, two on either side of the puborectalis muscle and the third in the anterior portion of the external anal sphincter, under ultrasonographic guidance [145]. At two months, nine of fourteen patients had symptomatic improvement with a decrease in rectocele depth and area and decrease tone during straining. At one year, no patient experienced incomplete or required digitally assisted rectal voiding.
BT use in the treatment of pelvic floor dyssenergia is still in its infancy with only small trials supporting its use. Many questions still remain such as the dose of BT, location of injection, use of ultrasound or electromyography, number of treatments, and combination with biofeedback. These questions need further study using placebo-controlled trials and larger sample sizes.

Chronic Idiopathic anal Pain
Chronic idiopathic anal pain is part of a rather ill-defined group of disorders termed chronic idiopathic perineal pain, which also includes proctalgia fugax and coccygodynia [160]. No objective abnormalities are found on clinical examination. The pathogenesis of the syndrome are unknown. There is no satisfactory treatment (anal stretch or surgery) for chronic anal pain. Eighteen patients who met the criteria for chronic idiopathic anal pain were studied. Treatment consisted of analgesics only in four patients, 0.2% nitroglycerin ointment in four, and ultrasound BT injection into the intersphincteric space in nine. Four patients were managed satisfactorily on analgesic treatment under the guidance of the hospital's pain clinic. Nitroglycerin ointment resulted in temporary pain relief in one of four patients. BT injection resulted in a permanent improvement in four patients, a temporary improvement in one patient, and no effect in four patients. Two patients had a colostomy, resulting in complete pain relief [160]. As in other syndromes based on muscular dystonia, some patients may benefit from BT injection.

Anal Fissure
Anal fissures are tears in the anoderm that start at the anal verge and can extend to the dentate line [161][162][163]. They can manifest into painful defecation and rectal bleeding. These fissures, which most commonly arise in the mid-posterior position of the anus, are thought to occur secondary to ischemia as a result of increased anal sphincter pressures and decreased blood flow [164,165]. Once chronic fissures develop, treatment options are aimed at interrupting this cycle by reducing sphincter tone using topical nitroglycerin, BT injection, oral nifedipine, or LIS performed surgically [165]. There are many reports on the efficacy of BT for this condition (Table 4).  These studies include several controlled trials comparing the toxin to either placebo or other modalities [6,170,173]. Clinical benefit is seen in the vast majority of patients, typically accompanied by reduction in resting anal sphincter pressure [175,178].
The exact site and dose of injection remains somewhat unsettled. Most of the trials to this point have evaluated BT administration at the point of the fissure, primarily, the posterior midline area of the anal verge. However, there is evidence that IAS fibrosis exists at the base of the fissure and is more prominent in this zone than other sites in the smooth muscle. This fibrosis may decrease the effects of BT on sphincter relaxation, thus delaying fissure healing. A study to evaluate this theory was conducted on 50 patients with posterior anal fissures who were either given 20 BT units lateral to the posterior fissure or 20 BT units on each side of the anterior midline [175]. After two months, a healing scar was observed in 15 patients (60%) of the posterior midline group and in 22 patients (88%) of the anterior midline group (p = 0.025). Resting anal pressure was significantly different from the baseline values at 1 and 2 months in both groups, but the values were significantly lower in patients of the anterior midline group.
Another study evaluated 150 patients with posterior anal fissures were treated with BT injected in the IAS on each side of the anterior midline. Patients were randomized to receive either 20 BT units and, if the fissure persisted, were retreated with 30 units, or 30 units and retreated with 50 units, if the fissure persisted [178]. One month after the injection, examinations revealed complete healing in 55 patients (73%) in the group receiving the lower dose and 65 patients (87%) in the group receiving the higher dose (p = 0.04). Five patients from the second group reported a mild incontinence of flatus that lasted 2 weeks after the treatment and disappeared spontaneously. The values of the resting anal pressure (p = 0.3) and the maximum voluntary pressure (p = 0.2) did not differ between the two groups. However, after two months, healing rates were similar between the two groups (89% and 96%). The authors concluded that the higher dose was more effective, but the improved effectiveness was not seen at two months [178].
The gold standard for treatment for anal fissures is surgery, primarily LIS. However, surgical intervention is associated with a low complication rate resulting in fecal incontinence, hematoma, and wound infection. A study compared BT injection (20 to 30 units) and LIS [179]. Overall healing rates were similar in both groups at six months with 10 of 61 patients requiring a second BT injection at two months. However, the response rate was higher at 1 and 2 months in the sphincterotomy group; 82% (41/50) at day 28 and 98% (49/50) at the second month (p = 0.023 and p < 0.0001, respectively, compared with the BT group). The response to BT was not as durable as surgery at 12 months falling to a success rate 75.4% (46/61) with seven recurrences in the BT group, whereas it remained stable in the LIS group (94%, p = 0.008). Sphincterotomy was associated with a significantly higher complication rate, eight cases of anal incontinence versus none in the BT group (p < 0.001) [179]. Thus, it appears that surgery is still the more durable treatment option but associated with more complications. These results have been supported in a more recent study. Some investigators have recommended surgery in younger patients and those with high resting anal pressures, as this is a risk factor for recurrence. Older patients may benefit from BT injection as they may be at higher risk of fecal incontinence.
A recent meta-analysis showed that even though LIS is associated with a better healing rate and recurrence rate, BT treatment is superior to LIS in overall complication rates and incontinence rates [199]. Thus, some advantages BT offers to patients with anal fissure include a good tolerance of the procedure, an outpatient setting, and a low risk of incontinence. The results of the meta-analysis are in line with previous research [200]. Furthermore, in a recent study BT injection was used not only as a therapeutic tool but also as a diagnostic test to identify patients who would not be suitable for further surgical LIS if they developed temporary incontinence after BT injection [201]. Combination therapy such as nitroglycerine and BT has also been evaluated; it appears that this only results in a modest increase in the rate of healing [202,203].
BT injection is efficacious in the treatment of chronic anal fissures. With greater than 60% response rates noted at two months with further response to re-treatment, BT can be considered a viable treatment option when more conservative treatment fails. In elderly patients, in who rates of fecal incontinence after surgery may be increased, BT can be considered first-line treatment. Surgery is still the most durable treatment option, but the risks of fecal incontinence must be weighed carefully against the benefits of the procedure.
Thus, according to many authors we recommend a safety first approach and treat all patients medically in the first instance. We believe that specific indications for surgical intervention in patients with anal fissure include persistence/recurrence, noncompliance or intolerance to the medical treatment. Patients at higher incontinence risk can be evaluated by anorectal manometric and endoanal sonography test, or, at best, the patient should be offered a sphincter-sparing procedure. The need for further investigations imposes a cost increase. Furthermore, it is difficult to calculate the increased cost in the event of complications. Some of these patients may wish to avoid LIS and persist with an alternative medical therapy.
Recently, Mishra et al. concluded that both treatments (NO donors and BT) may be considered as first-line treatment even if less effective than surgery [204]. However, this view has been challenged by other observations based on smaller series, providing inferior evidence of efficacy. The results of some studies are so disappointing that it led Nelson and coworkers to conclude a Cochrane review stating that "medical therapy for chronic anal fissure... may be applied with a chance of cure that is only marginally better than placebo." [205]. We think that such conclusion is too pessimistic, and welcome further multi-center trials with appropriate methodology (intention-to-treat based selection of patients, doses, and injection technique) and adequate follow-up, to ascertain the safety and efficacy of the therapy. Moreover, the addition of multiple treatment modalities prolonged time to healing from initial evaluation, but allowed up to 75% of patients to avoid the need for permanent sphincter division while maintaining the highest rate of healing.
We believe that the introduction of conservative therapies, and especially of BT, in the treatment of these patients represents an innovation equal to the introduction of laparoscopy. The introduction of these therapies has made the treatment of anal fissure easier, in the outpatient setting, at a lower cost and without permanent complications. On the other hands, laparoscopy has led to an increase in the cost of a single surgical procedure, often with a higher incidence of complications than open surgery.
With regard to anal fissure, any conservative treatment used has lower costs than surgery [206]. Considering the three hypothetical scenarios reported in a recent paper, we found that the BT approach is more cost-effective than the ointment approach. In addition to cost reduction (on average 62% lower than the association NO donors plus surgery and on average 50% lower than the association CCA plus surgery), BT reduces the number of patients who need further surgery. Moreover, the preparation of incobotulinumtoxin A has a lower price than preparations onabotulinumtoxin A and abobotulinumtoxin A. This figure, given the similar clinical efficacy of the three formulations, would lead us to prefer the incobotulinumtoxin A [206]. It must be stressed, however, that the prices of the three formulations are not very dissimilar.
We believe that BT is a safe treatment for anal fissure; it should be considered the first-line therapy in patients with chronic anal fissure.

Other Anorectal Conditions
BT into the IAS has been applied both diagnostically and therapeutically after pull-though surgery for Hirschsprung's disease. Minkes and Langer prospectively evaluated 18 such children who underwent BT injection (total dose 15-60 units) into 4 quadrants of the sphincter [207]. The authors have been showed improvement in 12 patients; improvement was sustained beyond 6 months in 5 of these patients.
A total of 33 children with surgically treated Hirschsprung's disease treated with intrasphincteric BT injection for obstructive symptoms were analyzed in a recent study [208]. The median time of follow up was 7.3 years. A median of two injections were given. Initial improvement was achieved in 76%, with a median duration of 4.1 months. Proportion of children hospitalized for enterocolitis decreased after treatment from 19 to 7. A good long-term response was found in 49%. Basson and coworkers have been studied 43 patients with idiopathic constipation, Hirschsprung's disease, anorectal malformation and GIT dysmotility [209]. A total dose of 200 BT units has been injected. Successful outcomes occurred in 72% patients after the first BT treatment, and 25% required further surgical management of their symptoms.
Pain after hemorrhoidectomy appears to be multifactorial; it seems be conceivable that IAS spasm is believed to play an important role [210]. The BT role in reducing pain after hemorrhoidectomy has been assessed in a double-blind study [211]. BT-treated patients have significantly less pain toward the end of the first week after surgery.

Conclusions
BT use for treatment of spastic GIT disorders has gained widespread acceptance over the last 15 years, especially in the treatment of chronic anal fissures and achalasia. Its administration is generally safe and relatively non-invasive compared to many of the alternatives. However, its short-term duration of action in disorders that affect patients long-term is its most significant negative. Repeated administrations with are generally necessary, with noted loss of efficacy.
The use of BT in many GIT disorders, although exciting, has not reached a level supported by clinical evidence. Further trials are needed with corresponding research to elucidate the pathophysiolgy of the spastic GIT disorders.