Introduction
Background
Achalasia is an esophageal motor disorder characterized by increased lower esophageal sphincter (LES) pressure, diminished-to-absent peristalsis in the distal portion of the esophagus composed of smooth muscle, and lack of a coordinated LES relaxation in response to swallowing.
Primary achalasia is the most common subtype and is associated with loss of ganglion cells in the esophageal myenteric plexus. These important inhibitory neurons induce LES relaxation and coordinate proximal-to-distal peristaltic contraction of the esophagus.
Secondary achalasia is relatively uncommon. This condition exists when a process other than intrinsic disease of the esophageal myenteric plexus is the etiology. Examples of maladies causing secondary achalasia include certain malignancies, diabetes mellitus, and Chagas disease.
Sir Thomas Willis first described achalasia in 1674. Willis successfully treated a patient by dilating the LES with a cork-tipped whalebone. Not until 1929 did Hurt and Rake first realize that the primary pathophysiology resulting in achalasia was a failure in LES relaxation.
Pathophysiology
The exact etiology of achalasia is not known. The most widely accepted current theories implicate autoimmune disorders, infectious diseases, or both. The last decade has witnessed much progress in the understanding of the cellular and molecular derangements in achalasia.
Degeneration of the esophageal myenteric plexus of Auerbach is the primary histologic finding. However, with early achalasia, a mixed inflammatory infiltrate of T cells, mast cells, and eosinophils is found in association with myenteric neural fibrosis and with a selective loss of inhibitory postganglionic neurons from the Auerbach plexus. In these patients with early achalasia, neurons of the myenteric plexus are relatively well preserved.
The inhibitory neurons produce nitric oxide (NO) and vasoactive intestinal peptide (VIP). NO and VIP are inhibitory neurotransmitters responsible for relaxation of the LES and for coordinated esophageal peristalsis. The loss of inhibitory neurons allows unopposed excitatory stimulation by postganglionic cholinergic neurons of the Auerbach plexus, which leads to a failure in LES relaxation and, eventually, to aperistalsis of the distal esophagus due to loss of the esophageal body latency gradient. Essentially, this means that this portion of the esophagus is unable to relax and subsequently generate a proper, sequential peristaltic wave.
Clinically important features defined by this pathophysiology include the following:
- Peristalsis in the distal smooth muscle segment of the esophagus may be lost. Contractions occur, but they are weak; simultaneous; uncoordinated; and, therefore, nonpropulsive.
- The LES fails to relax, either partially or completely.
- LES pressure is elevated in some patients.
- The coordination of LES relaxation in response to swallowing and esophageal contraction is lost.
Frequency
United States
Achalasia is a relatively uncommon disease. In the United States, the incidence and prevalence approximate international rates.
International
Mayberry and Rhodes described the demographics of achalasia for the city of Cardiff, Wales, in 1926-1977 (Mayberry, 1980). The incidence of achalasia is 4-6 cases per million persons. The disease prevalence is approximately 8 cases per million population. Mayberry and Atkinson also estimated an annual incidence of 1-2 cases per 200,000 persons in the area of Nottingham, England (Mayberry, 1985). Rates may be slightly higher in South America because of the prevalence of Chagas disease there.
Mortality/Morbidity
- Failure of the LES to relax and decrements in esophageal peristalsis lead to stasis and the retention of foodstuffs and upper gastrointestinal secretions in the esophagus. The primary morbidity associated with this effect is esophagitis, which is readily recognized on endoscopic examination.
- The mass of pooled secretions and solid materials places the patient at risk for aspiration. According to Vantrappen and associates, as many as 30% of patients with achalasia report nocturnal coughing episodes (Vantrappen, 1971). Nocturnal coughing can lead to aspiration pneumonia, which is a serious complication.
- Patients with achalasia are at increased risk for esophageal carcinoma, compared with the general population. According to Wychulis et al and Lortat-Jacob et al, 2-7% of patients with achalasia have an esophageal carcinoma (Wychulis, 1971; Lortat-Jacob, 1969). Esophageal carcinoma and a greatly dilated esophagus are found more frequently in patients with long-standing disease than in patients with early-stage achalasia.
Race
No racial predilection has been described for achalasia.
Sex
Achalasia has no sex predilection.
Age
The incidence of achalasia peaks in those aged 20-40 years. The disease has been diagnosed in infants and in patients well into their 80s (Nihoul-Fekete, 1991).
Anatomy
The average length of the esophagus is 25 cm. As illustrated by Clemente, the esophagus begins just distal to that portion of the inferior pharyngeal constrictor muscle that originates on the cricoid cartilage (Clemente, 1981). The esophagus terminates at the gastroesophageal junction. By convention, the esophagus is typically divided into 3 segments: (1) the cervical esophagus, (2) the thoracic esophagus, and (3) the abdominal esophagus.
The esophageal musculature is composed of an outer longitudinal layer and an inner circular layer. According to Meyer and colleagues, the esophageal musculature is striated in the proximal 5% of the organ (Meyer, 1986). The following 30-40% contains both striated and smooth muscle. The distal 50-60% is composed solely of smooth muscle, which is relevant because the denervation that is the hallmark of achalasia affects the smooth-muscle segment of the esophagus.
Esophageal contraction and peristalsis are mediated by parasympathetic fibers traveling in the vagus nerves. The dorsal motor nucleus of the vagus nerve is responsible for controlling the smooth muscle. In contrast, the nucleus ambiguus controls skeletal muscle.
The esophagus contains 2 major nerve plexuses: the Auerbach plexus and the Meissner plexus. The Auerbach, or myenteric, plexus is embedded between the longitudinal and circular layers of esophageal muscle. Neurons of the Auerbach plexus receive input from vagal preganglionic efferent fibers responsible for smooth muscle control. The Meissner plexus can be found in the submucosa of the esophagus. This plexus of nerves carries afferent information from the esophagus to the vagal parasympathetic and thoracic sympathetic nerves, then onward to the central nervous system.
Presentation
Dysphagia is the most common presenting symptom in patients with achalasia. The ingestion of either solids or liquids can result in dysphagia, though dysphagia for solids is more common. Emotional stress and the ingestion of cold liquids are well-known exacerbating or precipitating factors. The natural history varies. Some patients notice that the dysphagia reaches a certain point of severity and then stops progressing. In others, the dysphagia continues to worsen, resulting in decreased oral intake, malnutrition, and inanition. Therefore, weight loss is included in the complex of signs and symptoms associated with achalasia, and it is usually a sign of advanced esophageal disease.
Approximately 25-50% of patients with dysphagia report episodes of chest pain, which are frequently induced by eating. Typically, chest pain is described as being retrosternal; this is a more common feature in patients with early or so-called vigorous achalasia. As the disease progresses and as the esophageal musculature fails, chest pain tends to abate or disappear.
As many as 80-90% of patients with achalasia experience spontaneous regurgitation of undigested food from the esophagus during the course of the disease. Some learn to induce regurgitation to relieve the retrosternal discomfort related to the distended esophagus.
As the disease progresses, the likelihood that aspiration will occur increases. As a result, some patients may present with signs or symptoms of pneumonia or pneumonitis. Lung abscesses, bronchiectasis, and hemoptysis are some of the more severe pulmonary consequences of achalasia-associated aspiration.
Patients with achalasia are at increased risk for esophageal cancer. When esophageal cancer occurs, it is usually found in patients with a long history of achalasia.
Preferred Examination
The radiologic examination of choice in the diagnosis of achalasia is a barium swallow study performed under fluoroscopic guidance.
A diagnosis of achalasia supported by the results of radiologic studies must always be confirmed by performing upper gastrointestinal endoscopy and esophageal manometry. These tests allow the direct evaluation and inspection of the esophageal mucosa and an objective measurement of esophageal contractility.
Endoscopy, supplemented by biopsy when necessary, helps in excluding gastroesophageal malignancies, fungal or bacterial infections, and other disease processes that can mimic achalasia.
Manometry must be considered the criterion standard for diagnosis of the disease. Manometric findings consistent with achalasia include incomplete LES relaxation, which is present in more than 80% of patients; elevated LES pressure, which is present in some patients; and diminished-to-absent peristalsis in the distal esophagus.
If manometric findings are normal in a patient with clinical symptoms or radiographic evidence of achalasia, a condition termed pseudoachalasia may be present. Causes of pseudoachalasia include esophageal and gastric malignancies and other tumors involving distal esophagus or LES. In patients with these conditions, endoscopy with biopsy analysis and CT can be helpful.
Limitations of Techniques
A fluoroscopically guided barium swallow study that demonstrates 1 or more findings (see Radiograph) is highly suggestive of achalasia. However, a definitive diagnosis can be made only by means of esophageal manometry, preferably with the addition of upper endoscopy.
Conversely, normal findings on barium swallow study do not completely exclude achalasia, especially in its early stages. This situation is when esophageal manometry is most valuable, because the physiologic derangements associated with achalasia precede the development of the anatomic findings discernible by using radiographic studies.
Differential Diagnoses
Colon, Adenocarcinoma
Esophagus, Carcinoma
Gastric Carcinoma
Scleroderma, Thoracic
Other Problems to Be Considered
Amyloidosis
Chagas disease
Collagen-vascular disease
Lymphoma
Pseudoachalasia
Presbyesophagus
Diffuse esophageal spasm
Esophageal candidiasis
Diabetes mellitus
More on Achalasia |
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Further Reading
Keywords
esophageal motor disorder, cardiospasm, primary achalasia, secondary achalasia, LES relaxation, lower esophageal sphincter relaxation, failure of LES relaxation, dysphagia, pseudoachalasia, esophageal distention, bird beak deformity, atonic esophagus, primary achalasia, secondary achalasia
