The esophagus functions solely to deliver food from the mouth to the stomach where the process of digestion can begin. Efficient transport by the esophagus requires a coordinated, sequential motility pattern that propels food from above and clears acid and bile reflux from below. Disruption of this highly integrated muscular motion limits delivery of food and fluid, as well as causes a bothersome sense of dysphagia and chest pain. Disorders of esophageal motility are referred to as primary or secondary esophageal motility disorders and categorized according to their abnormal manometric patterns. See the images below.
The tubular esophagus is a muscular organ, approximately 25 cm in length, and has specialized sphincters at proximal and distal ends. The upper esophageal sphincter (UES) is comprised of several striated muscles, creating a tonically closed valve and preventing air from entering into the gastrointestinal tract. The lower esophageal sphincter (LES) is composed entirely of smooth muscle and maintains a steady baseline tone to prevent gastric reflux into the esophagus.
The body of the esophagus is similarly composed of 2 muscle types. The proximal esophagus is predominantly striated muscle, while the distal esophagus and the remainder of the GI tract contain smooth muscle. The mid esophagus contains a graded transition of striated and smooth muscle types. The muscle is oriented in 2 perpendicular opposing layers: an inner circular layer and an outer longitudinal layer, known collectively as the muscularis propria. The longitudinal muscle is responsible for shortening the esophagus, while the circular muscle forms lumen-occluding ring contractions.
The coordination of these simultaneously contracting muscle layers produces the motility pattern known as peristalsis. Peristalsis is a sequential, coordinated contraction wave that travels the entire length of the esophagus, propelling intraluminal contents distally to the stomach. The LES relaxes during swallows and stays opened until the peristaltic wave travels through the LES, then contracts and redevelops resting basal tone. Low peristaltic amplitudes normally occur at the transition zone between the striated and smooth muscle portions; however, the peristalsis is uninterrupted.
Primary peristalsis is the peristaltic wave triggered by the swallowing center. The peristaltic contraction wave travels at a speed of 2 cm/s and correlates with manometry-recorded contractions. The relationship of contraction and food bolus is more complex because of intrabolus pressures from above (contraction from above) and the resistance from below (outflow resistance).
The secondary peristaltic wave is induced by esophageal distension from the retained bolus, refluxed material, or swallowed air. The primary role is to clear the esophagus of retained food or any gastroesophageal refluxate.
Tertiary contractions are simultaneous, isolated, dysfunctional contractions. These contractions are nonperistaltic, have no known physiologic role, and are observed with increased frequency in elderly people. Radiographic description of this phenomenon has been called presbyesophagus.
Esophageal motility disorders
Esophageal motility disorders are not uncommon in gastroenterology. The spectrum of these disorders ranges from the well-defined primary esophageal motility disorders (PEMDs) to very nonspecific disorders that may play a more indirect role in reflux disease and otherwise be asymptomatic. Esophageal motility disorders may occur as manifestations of systemic diseases, referred to as secondary motility disorders.
Esophageal motility disorders are less common than mechanical and inflammatory diseases affecting the esophagus, such as reflux esophagitis, peptic strictures, and mucosal rings. The clinical presentation of a motility disorder is varied, but, classically, dysphagia and chest pain are reported. In 80% of patients, the cause of a patient's dysphagia can be suggested from the history, including dysmotility of the esophagus. Before entertaining a diagnosis of a motility disorder, first and foremost, the physician must evaluate for a mechanical obstructing lesion.
Esophageal motility disorders discussed in this article include the following:
Spastic esophageal motility disorders, including diffuse esophageal spasm (DES), nutcracker esophagus, and hypertensive LES
Nonspecific esophageal motility disorder (inefficient esophageal motility disorder)
Secondary esophageal motility disorders related to scleroderma, diabetes mellitus, alcohol consumption, psychiatric disorders, and presbyesophagus
Primary esophageal motility disorders are idiopathic in nature, but postviral, infectious, environmental, and genetic factors have been hypothesized.
The pathophysiology of the primary esophageal motility disorders is poorly defined, with the exception of achalasia. The underlying cause of all the primary motility disorders remains elusive. The secondary motility disorders, such as scleroderma esophagus or esophageal motility disorder of diabetes, are better understood from the standpoint of the preexisting underlying disorders.
Achalasia is the best defined primary motility disorder and the only one with an established pathology. The predominant neuropathologic process of achalasia involves the loss of ganglion cells from the wall of the esophagus, starting at the LES and developing proximally. The degree of ganglion cell loss parallels the disease duration such that, at 10 years, ganglion cells are likely completely absent. At the LES, the loss of inhibitory nerves is demonstrated by loss of nitric oxide synthase and vasoactive intestinal peptide (VIP) immunohistochemistry staining. Variable amounts of inflammatory cells have been described within the myenteric plexus along with the disappearing nerves. In the peristaltic esophageal body, achalasia is characterized by a loss of intrinsic acetylcholine-containing nerves.
Extrinsic nerves may also be affected, characterized by Wallerian degeneration of the axoplasm and myelin sheaths within the vagus nerve and dorsal motor nucleus. Anatomically, the circular muscle layer at the LES is thickened, but, microscopically, individual muscle cells are grossly normal.
The physiologic process of achalasia is correlated most directly to the loss of the inhibitory nerves at the sphincter, resulting in failure of the LES to completely relax and causing relative obstruction. Manometry may reveal elevated LES pressure greater than 40 mm Hg in more than 60% of patients; however, hypertensive LES is not universal or required for the manometric diagnosis. The loss of nerves along the esophageal body causes aperistalsis, leading to stasis of ingested food and subsequent dilation of the esophagus. Nonperistaltic isolated contractions or low-amplitude simultaneous contractions of the esophageal body may be observed. If high-amplitude (>60 mm Hg) simultaneous contractions occur, the entity is categorized as vigorous achalasia, which may represent an early stage of classic achalasia. Physiologic characteristics of achalasia are additionally useful in assisting with establishing the diagnosis through chemical challenge testing.
With the partial ganglion cell loss in patients with achalasia, edrophonium (acetylcholine esterase inhibitor) increases LES pressure while atropine (muscarinic antagonist) decreases LES pressure. This characteristic likely explains why the botulinum toxin (acetylcholine release inhibitor) may have therapeutic benefit in patients with achalasia.
Spastic motility disorders of the esophageal body
No documented abnormalities exist regarding the distribution of myenteric neurons in patients diagnosed with spastic motility disorders of the esophageal body, but diffuse fragmentation of vagal filaments, increased endoneural collagen, and mitochondrial fragmentation are described. There appears to be a functional imbalance between excitatory and inhibitory postganglionic pathways, disrupting the coordinated components of peristalsis. In DES, muscular hypertrophy or hyperplasia has been described in the distal two thirds of the esophagus. Muscle wall thickening has been described in patients who are asymptomatic and, conversely, has been absent in some patients with typical symptoms and manometric findings. This controversial finding causes difficulty in attributing symptoms or manometric abnormalities to muscle structure changes. In addition, anxiety states may also play a role in some patients.
In scleroderma, the primary defect in this systemic process is related to smooth muscle atrophy and fibrosis. Esophageal dysmotility develops as the smooth muscle of the esophagus is replaced by scar tissue, gradually leading to progressive loss of peristalsis and a weakening of LES. Motility is preserved at the proximal striated muscle portion of the esophagus.
United States data
Esophageal motility disorders, excluding achalasia, lack population-based studies. The 2 best-characterized motility disorders, achalasia and DES, represent only a small percentage of diagnosed motility disorders. The incidence of achalasia is 1-3 case per 100,000 population per year.  As with any other chronic illness, prevalence exceeds incidence significantly. Familial clustering is observed, but a genetic relationship is not established. Nutcracker esophagus is the most common motility disorder (>40% of all motility disorders diagnosed), but it is the most controversial in significance.
The incidence of esophageal dysmotility appears to increased in patients with spinal cord injury (SCI).  In a study of 12 patients with paraplegia (level of injury between T4-T12), 13 patients with tetraplegia (level of injury between C5-C7), and 14 able-bodied individuals, Radulovic et al found 21 of the 25 patients (84%) with SCI had at least one esophageal motility anomaly compared to 1 of 14 able-bodied subjects (7%). Among the anomalies seen in SCI patients were type II achalasia (12%), type III achalasia (4%), esophagogastric junction outflow obstruction (20%), hypercontractile esophagus (4%), and peristaltic abnormalities (weak peristalsis with small or large defects or frequent failed peristalsis) (48%). 
Altered esophageal motility is sometimes seen in patients with anorexia nervosa.  It is also seen in patients following eradication of esophageal varices by endoscopic sclerotherapy, in association with an increased number of endoscopic sessions but not with manometric parameters.  Features of esophageal motility after endoscopic sclerotherapy are a defective lower sphincter and defective and hypotensive peristalsis.
In Europe, the incidence of achalasia is similar to that of the United States.
Race-, sex-, and age-related demographics
Racial and environmental differences in the incidence of achalasia and other esophageal motility disorders might be present; however, because of the low incidence of disease and underdiagnosis in developing countries, these differences have not been demonstrated. Racial differences in the incidence of achalasia and other esophageal motility disorders have not been established.
Achalasia affects both sexes in equal numbers. No reliable information for other motility disorders exists.
Achalasia commonly presents in the fifth decade but rarely may develop in children as well as in elderly persons.
Achalasia is a progressive disease that requires chronic therapy. Depending on the rate and extent of disease progression, therapy might include endoscopic and surgical interventions. Advanced achalasia can lead to malnutrition, dehydration, and aspiration.
Even after therapy, patients continue to have mild symptoms related to aperistaltic esophagus and, thus, will want to still follow careful eating habits.
Scleroderma is a systemic disease with a progressive nature. Systemic complications are the major cause of mortality.
Significant acid reflux might lead to disabling symptoms, caused by reflux or its complications.
Spastic esophageal motility disorders
Whether or not symptomatic relief is achieved, the prognosis in patients with spastic esophageal motility disorders is favorable. Life expectancy is not affected, and weight loss is rare.
If symptoms progress, then the workup should be repeated because DES can progress to achalasia.
Achalasia is associated with significant and progressive symptomatic discomfort. When advanced, this condition can lead to such severe dysphagia that malnutrition, weight loss, and dehydration can develop. Increased incidence of both esophageal squamous cell and adenocarcinoma is observed in patients with long-standing achalasia. Therapeutic procedures and operations are associated with a small but significant risk of mortality and morbidity.
Spastic esophageal motility disorders are associated with symptomatic discomfort but do not lead to the severity of dysphagia observed in patients with achalasia. Chest pain is, in fact, a more common complaint that may precipitate emergency room visits and cardiologic evaluations.
Scleroderma esophagus is associated with severe and progressive acid reflux symptoms and complications. Associated complications, including strictures, Barrett esophagus, and adenocarcinoma of the esophagus, are the concern.
Achalasia and squamous cell carcinoma
With achalasia, the risk of squamous cell carcinoma of the esophagus is higher than that of the general population. However, no studies to date have shown convincing evidence that surveillance is worthwhile.
The pathogenesis is not well documented, but chronic mucosal irritation is incriminated.
Squamous cell carcinoma usually develops several years after the diagnosis of achalasia. The risk typically starts increasing after approximately 10 years of having the disease process. At the time of diagnosis, the esophagus usually is dilated, and the tumor is advanced.
Patients should be counseled about their disease. They should be well informed about its lifelong nature. Possible complications, therapeutic options, expected outcomes, and dietary modifications should be explained.
Reassurance is important in patients with spastic motility disorders, especially in the setting of noncardiac chest pain.
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