Achalasia overview

# Overview
Achalasia is a primary esophageal motility disorder of unknown etiology.In this disorder, the smooth muscle layer of the esophagus has impaired peristalsis (muscular ability to move food down the esophagus), and the lower esophageal sphincter (LES) fails to relax properly in response to swallowing due to absent enteric neurons.  It should be differentiated from pseudoachalasia (caused by neoplastic infiltration of myenteric neurons) and secondary achalasia (caused by extrinsic procedures such as previous fundoplication and gastric banding).  Trypanosoma cruzi infection causing Chagas disease can also result in achalasia.  It is an incurable chronic condition.

# Historical Perspective
Achalasia is Greek for failure to relax and has been known for more than 300 years BC. The first successful esophagomyotomy was done in 1913 while laparoscopic esophagomyotomy was described in 1991.

# Classification
Achalasia can be classified according to the pattern of abnormal peristalsis into three types. Different types of achalasia are shown to have different responses to therapies with type II having the best prognosis.

# Pathophysiology
Achalasia is caused by degeneration of myenteric neurons, resulting from immune system activation.  Evidence for antigens responsible for such immune system activation still remain inconclusive, however, viral antigens such as HSV-1, HPV, measles have been shown to play a role in achalasia pathogenesis.  Genetic factors such as HLA class II alleles also predispose to achalasia development.

# Causes
Achalasia is chronic esophageal motility disorder.  The most common form is primary achalasia, which has no known underlying cause. It is due to the failure of distal esophageal inhibitory neurons. However, a small proportion occurs secondary to other conditions, such as esophageal cancer or Chagas disease.

# Differentiating Achalasia overview from Other Diseases
Achalasia must be differentiated from other causes of dysphagia, odynophagia and food regurgitation such as GERD, esophageal adenocarcinoma, esophageal stricture, esophageal webs, motor disorders such as myasthenia gravis, stroke, Zenker's diverticulum, diffuse esophageal spasm, systemic sclerosis and Plummer Vinson syndrome.

# Epidemiology and Demographics
The incidence of Aachalasia is approximately ~ 1 per 100,000. There is no predilection to any age and has the same prevalence in both whites and non-whites.

# Risk Factors
The most potent risk factor in the development of achalasia is Allgrove syndrome. Other risk factors include herpes infection, measles infection, autoimmune diseases, and HLA type 2.

# Screening
According to the USPSTF, no screening measures are recommended for achlasia.

# Natural History, Complications, and Prognosis
If left untreated, the disease can progress causing complications such as candida esophagitis and esophageal perforation. However, achalasia does not alter the lifespan of the patients. Common complications include GERD, Barrett's esophagus, and aspiration pneumonia. The prognosis is good with cure rate of 60-90% after surgical interventions.

# Diagnosis

## History and Symptoms
The main symptoms of achalasia are dysphagia, regurgitation of undigested food, retrosternal chest pain and weight loss. Dysphagia involves both fluids and solids and progressively worsens over time. The chest pain experienced, also known as cardiospasm and non-cardiac chest pain can often be mistaken for a heart attack. Food and liquid, including saliva, can be retained in the esophagus and may be aspirated into the lungs. Some people may also experience coughing when lying in a horizontal position.

## Physical Examination
Physical examination is usually non significant as the diagnosis is dependent on the symptoms and the radiological tests. Patients with achalasia usually appear calm and in no acute distress. Physical examination of patients with achalasia is usually remarkable for weight loss and oral cavity ulcers.

## Laboratory Findings
A Laboratory work-up is usually non significant as the diagnosis is dependent on the symptoms and the radiological tests. Laboratory findings in patients with the diagnosis of achalasia may include microcytic hypochromic anemia and vitamin deficiencies.

## Chest Xray
Achalasia is caused by insufficient lower esophageal sphincter (LES) relaxation causing obstruction at gastro-esophageal junction.  It leads to absent peristalsis and stasis of food in esophagus.   To perform an X ray with barium swallow, the patient swallows a barium solution, which fails to pass smoothly through the lower esophageal sphincter. An air-fluid margin is seen over the barium column due to the lack of peristalsis. Narrowing is observed at the level of the gastroesophageal junction ("bird's beak" or "rat tail" appearance of the lower esophagus). Esophageal dilation is present in varying degrees as the esophagus is gradually stretched by retained food. A five-minute timed barium swallow is useful to measure the effectiveness of treatment.

## CT
CT scan may show dilatation of the esophagus with air fluid levels in long-standing cases. CT scan may be used to exclude pseudoachalasia, or achalasia symptoms resulting from a different cause, usually esophageal cancer.

## MRI
MRI can show the same findings  found in CT scan such as esophageal dilation and air fluid levels. MRI can also reveal the underlying cause of achalasia such as esophageal adenocarcinoma.

## Ultrasound
Endoscopic ultrasound is required in cases where malignancy is suspected.

## Other Imaging findings
Esophagogastroduodenoscopy is complementary to manometry in diagnosing achalasia. It is indicated primarily to rule out any mechanical obstruction or pseudoachalasia (neoplastic iniltration).

## Other Diagnostic Studies
Manometry is the key diagnostic test for achalasia.  Barium esophagram and esophagogastroduodenoscopy are complimentry to manometry in diagnosing achalasia.  Manometric findings such as absent peristalsis or incomplete LES relaxation without any mechanical obstruction characterize achalasia.  Other supportive manometric findings in achalasia include raised basal LES pressure, increased intraoesophageal pressure and simultaneous non-propagating contractions.

# Treatment

## Medical Therapy
Botulinum toxin, calcium channel blockers and nitrates are the most commonly used medical therapies for achalasia.  However, they are not very effective and used only when pneumatic dilation and surgical procedures cannot be performed in high risk patients.

## Surgery
Most effective treatment options for achalasia are pneumatic dilation and laparoscopic myotomy.  Pneumatic dilation works by flattening the waist of insufficiently relaxed LES by placing a balloon at LES.  Laparoscopic myotomy relaxes LES by dissecting outer muscular layers of the esophagus and sparing the inner mucosal layer.

## Primary prevention
There are no primary preventive measures available for achalasia.

## Secondary prevention
Many of the causes of achalasia are not preventable. However, treatment of the disorder may help to prevent complications.