Etiopathological aspects of achalasia: lessons learned with Hirschsprung's disease

Disorders of the enteric nervous system - a holistic view

The enteric nervous system (ENS) is the largest division of the peripheral nervous system and closely resembles components and functions of the central nervous system. Although the central role of the ENS in congenital enteric neuropathic disorders, including Hirschsprung disease and inflammatory and functional bowel diseases, is well acknowledged, its role in systemic diseases is less understood. Evidence of a disordered ENS has accumulated in neurodegenerative diseases ranging from amyotrophic lateral sclerosis, Alzheimer disease and multiple sclerosis to Parkinson disease as well as neurodevelopmental disorders such as autism. The ENS is a key modulator of gut barrier function and a regulator of enteric homeostasis. A 'leaky gut' represents the gateway for bacterial and toxin translocation that might initiate downstream processes. Data indicate that changes in the gut microbiome acting in concert with the individual genetic background can modify the ENS, central nervous system and the immune system, impair barrier function, and contribute to various disorders such as irritable bowel syndrome, inflammatory bowel disease or neurodegeneration. Here, we summarize the current knowledge on the role of the ENS in gastrointestinal and systemic diseases, highlighting its interaction with various key players involved in shaping the phenotypes. Finally, current flaws and pitfalls related to ENS research in addition to future perspectives are also addressed.

New insights into the pathophysiology of achalasia and implications for future treatment

Idiopathic achalasia is an archetype esophageal motor disorder, causing significant impairment of eating ability and reducing quality of life. The pathophysiological underpinnings of this condition are loss of esophageal peristalsis and insufficient relaxation of the lower esophageal sphincter (LES). The clinical manifestations include dysphagia for both solids and liquids, regurgitation of esophageal contents, retrosternal chest pain, cough, aspiration, weight loss and heartburn. Even though idiopathic achalasia was first described more than 300 years ago, researchers are only now beginning to unravel its complex etiology and molecular pathology. The most recent findings indicate an autoimmune component, as suggested by the presence of circulating anti-myenteric plexus autoantibodies, and a genetic predisposition, as suggested by observed correlations with other well-defined genetic syndromes such as Allgrove syndrome and multiple endocrine neoplasia type 2 B syndrome. Viral agents (herpes, varicella zoster) have also been proposed as causative and promoting factors. Unfortunately, the therapeutic approaches available today do not resolve the causes of the disease, and only target the consequential changes to the involved tissues, such as destruction of the LES, rather than restoring or modifying the underlying pathology. New therapies should aim to stop the disease at early stages, thereby preventing the consequential changes from developing and inhibiting permanent damage. This review focuses on the known characteristics of idiopathic achalasia that will help promote understanding its pathogenesis and improve therapeutic management to positively impact the patient’s quality of life.

Pathogenesis of achalasia

Achalasia is a kind of esophageal motility disorder, and it is mainly characterized by loss of the peristalsis of the esophagus during swallowing and insufficient lower esophageal sphincter (LES) relaxation. Primary achalasia is mainly due to the lack of inhibitory nerve fibers in the esophageal myenteric nerve plexus. However, the exact pathogenesis of the disease is still clear. This paper reviews recent progress in understanding the pathogenesis of achalasia.

[Peroral endoscopic myotomy for treatment of achalasia. Literature review and own initial experience]

Peroral endoscopic myotomy (POEM) is a new, purely endoscopic procedure for treatment of achalasia. Due to the lack of incisions POEM can be regarded as a true NOTES procedure. With POEM a myotomy is created in a similar fashion to the previous standard treatment, laparoscopic Heller myotomy (LHM). The relatively free choice of length and localization of the myotomy may be regarded as advantages of POEM. The procedure starts with a mucosal incision (mucosal entry) followed by preparation of a submucosal tunnel crossing the esophagogastric junction and creation of a myotomy in an antegrade direction before the mucosal access is closed with endoscopic clip placement. Since the first description of the application of POEM in humans in 2010 by the pioneer Haruhiro Inoue, Yokohama, Japan, it has been used increasingly and investigated in some centers in Asia, the U.S.A. and also Europe. The results are very promising. Although the procedure is technically demanding it can be performed safely with low complication rates. The POEM procedure achieves very good control of dysphagia and gastroesophageal reflux witch is only a rare side-effect witch is well-controllable with proton pump inhibitors (PPI). We review the currently available data from the literature and present our own initial series of  14 patients treated with POEM.

Phenotypic similarities and differences in patients with a p.Met112Ile mutation in SOX10

Waardenburg syndrome (WS) is characterized by an association of pigmentation abnormalities and sensorineural hearing loss. Four types, defined on clinical grounds, have been delineated, but this phenotypic classification correlates imperfectly with known molecular anomalies. SOX10 mutations have been found in patients with type II and type IV WS (i.e., with Hirschsprung disease), more complex syndromes, and partial forms of the disease. The phenotype induced by SOX10 mutations is highly variable and, except for the neurological forms of the disease, no genotype-phenotype correlation has been characterized to date. There is no mutation hotspot in SOX10 and most cases are sporadic, making it particularly difficult to correlate the phenotypic and genetic variability. This study reports on three independent families with SOX10 mutations predicted to result in the same missense mutation at the protein level (p.Met112Ile), offering a rare opportunity to improve our understanding of the mechanisms underlying phenotypic variability. The pigmentation defects of these patients are very similar, and the neurological symptoms showed a somewhat similar evolution over time, indicating a potential partial genotype-phenotype correlation. However, variability in gastrointestinal symptoms suggests that other genetic factors contribute to the expression of these phenotypes. No correlation between the rs2435357 polymorphism of RET and the expression of Hirschsprung disease was found. In addition, one of the patients has esophageal achalasia, which has rarely been described in WS.

The role of Botulinum toxin injection in the management of achalasia

PURPOSE OF REVIEW

Botulinum toxin injection into the lower esophageal sphincter is an established therapy for the treatment of achalasia. This review will highlight recent studies that shed light on the role of Botulinum toxin injection in the management of achalasia.

RECENT FINDINGS

Recent studies have shown that Botulinum toxin injection is the most common initial endoscopic therapy for achalasia, most likely due to its safety and ease of administration. However, this trend represents a deviation from recent guidelines which consider Botulinum toxin injection less efficacious than alternative treatments like pneumatic dilation and laparoscopic Heller myotomy. Over the past decade, multiple commercial formulations of Botulinum toxin injection have been introduced, but the techniques, indications, and therapeutic efficacy for Botulinum toxin have largely remained unchanged. This review will evaluate recent guidelines, consensus articles, meta-analyses, and landmark studies to expound on the short and long-term efficacy of Botulinum toxin, injection dosages, and technique, as well as its efficacy compared to pneumatic dilation, myotomy, and combination therapy.

SUMMARY

Despite its relatively poor long-term efficacy, Botulinum toxin injection continues to play an important role in elderly patients with comorbidities and as salvage therapy for achalasia.

Pathogenesis of achalasia cardia

Achalasia cardia is one of the common causes of motor dysphagia. Though the disease was first described more than 300 years ago, exact pathogenesis of this condition still remains enigmatic. Pathophysiologically, achalasia cardia is caused by loss of inhibitory ganglion in the myenteric plexus of the esophagus. In the initial stage, degeneration of inhibitory nerves in the esophagus results in unopposed action of excitatory neurotransmitters such as acetylcholine, resulting in high amplitude non-peristaltic contractions (vigorous achalasia); progressive loss of cholinergic neurons over time results in dilation and low amplitude simultaneous contractions in the esophageal body (classic achalasia). Since the initial description, several studies have attempted to explore initiating agents that may cause the disease, such as viral infection, other environmental factors, autoimmunity, and genetic factors. Though Chagas disease, which mimics achalasia, is caused by an infective agent, available evidence suggests that infection may not be an independent cause of primary achalasia. A genetic basis for achalasia is supported by reports showing occurrence of disease in monozygotic twins, siblings and other first-degree relatives and occurrence in association with other genetic diseases such as Down’s syndrome and Parkinson’s disease. Polymorphisms in genes encoding for nitric oxide synthase, receptors for vasoactive intestinal peptide, interleukin 23 and the ALADIN gene have been reported. However, studies on larger numbers of patients and controls from different ethnic groups are needed before definite conclusions can be obtained. Currently, the disease is believed to be multi-factorial, with autoimmune mechanisms triggered by infection in a genetically predisposed individual leading to degeneration of inhibitory ganglia in the wall of the esophagus.