Esophageal Achalasia

Oesophageal achalasia, commonly referred to simply as achalasia, is a primary oesophageal motility disorder characterised by the failure of smooth muscle relaxation at the lower oesophageal sphincter (LOS) and the absence of normal peristalsis in the oesophageal body. This results in impaired transit of food and liquids from the oesophagus into the stomach. Although achalasia can occur in other parts of the gastrointestinal tract, such as rectal achalasia in Hirschsprung’s disease, the term without qualification usually denotes involvement of the oesophagus.

Background and Definition

The lower oesophageal sphincter is a specialised muscular zone located at the junction of the oesophagus and stomach. Its physiological role is to relax during swallowing to permit the passage of a food bolus and to remain tonically contracted at rest to prevent gastro-oesophageal reflux of gastric acid. In achalasia, this finely regulated mechanism fails. The sphincter remains abnormally contracted, and coordinated oesophageal peristalsis is lost, leading to functional obstruction.
The term achalasia is derived from Greek, meaning “lack of relaxation”, reflecting the defining pathophysiological feature of the disease.

Epidemiology and Classification

Achalasia is a rare condition, with an incidence of approximately one case per 100,000 individuals per year. It affects both sexes equally and may present at any age, although it is most commonly diagnosed between the third and sixth decades of life.
Achalasia is broadly classified into:

• Primary (idiopathic) achalasia, which accounts for the majority of cases and has no identifiable underlying cause.
• Secondary achalasia, which occurs as a consequence of other conditions such as oesophageal carcinoma, Chagas disease, or rare genetic syndromes including Triple A (Allgrove) syndrome.

Pathophysiology and Mechanism

Normal oesophageal motility depends on a balance between excitatory and inhibitory neurotransmitters within the myenteric (Auerbach’s) plexus. Excitatory mediators include acetylcholine and substance P, while inhibitory mediators include nitric oxide and vasoactive intestinal peptide.
In achalasia, there is selective loss of inhibitory ganglion cells, particularly the non-adrenergic, non-cholinergic neurons. This leads to unopposed excitatory activity, resulting in:

• Increased resting tone of the lower oesophageal sphincter
• Incomplete or absent sphincter relaxation during swallowing
• Aperistalsis of the oesophageal body

Histological studies of oesophageal tissue often reveal inflammatory infiltrates composed predominantly of CD8-positive cytotoxic T lymphocytes, along with variable numbers of eosinophils and mast cells. Progressive loss of ganglion cells and neurofibrosis are seen, suggesting an autoimmune process, possibly triggered by viral infection. Genetic and neurodegenerative contributions have also been proposed.

Stages and Morphological Progression

Achalasia is a progressive disorder, and long-standing disease results in characteristic structural changes to the oesophagus. Radiological and clinical staging is commonly described:

• Second stage: Oesophageal dilatation of approximately 4–5 cm, with smooth tapering at the distal end producing a classic bird’s beak appearance on barium swallow.
• Third stage: Further dilatation, often reaching around 5–7 cm, with increasing stasis of food and fluid.
• Fourth stage (late-stage or end-stage achalasia): Marked dilatation exceeding 8 cm, with elongation and tortuosity of the oesophagus, often described as a sigmoid or “burnt-out” oesophagus.

At this stage, the oesophagus may function as a static reservoir rather than an active conduit, a condition known as megaoesophagus.

Clinical Features and Symptoms

The hallmark symptom of achalasia is dysphagia, affecting both solids and liquids from an early stage. Unlike mechanical obstruction, dysphagia in achalasia is typically progressive and non-selective.
Other common features include:

• Regurgitation of undigested food, especially when lying flat
• Retrosternal chest pain or discomfort, sometimes termed cardiospasm
• Weight loss and malnutrition
• Coughing or choking episodes due to aspiration, particularly at night

Chest pain may mimic angina or myocardial infarction and can be severe. As the disease advances, retained food and saliva accumulate within the dilated oesophagus and may be aspirated into the lungs, leading to recurrent respiratory infections or aspiration pneumonia.
In untreated mid- to late-stage achalasia, near-complete functional obstruction may occur. Food boluses remain within the oesophagus, progressively stretching its walls. Patients may experience forceful regurgitation without nausea due to passive emptying of the overdistended oesophagus. Over time, poor nutrient absorption results in cachexia, starvation, and increased mortality, although death is rarely recorded as directly attributable to achalasia.

Complications and Associated Conditions

Long-standing achalasia is associated with several important complications. Chronic food stasis predisposes to oesophageal candidiasis, which itself is a risk factor for malignant transformation. There is an established increased risk of oesophageal squamous cell carcinoma in patients with longstanding disease.
Other complications include:

• Megaoesophagus
• Aspiration pneumonia
• Oesophageal diverticula
• Severe malnutrition

Rarely, achalasia may present as part of a multisystem disorder, such as achalasia–microcephaly syndrome.

Diagnostic Evaluation

Achalasia may be mistaken for more common conditions such as gastro-oesophageal reflux disease, hiatus hernia, or functional disorders. Accurate diagnosis relies on specialised investigations.
Barium swallow radiography demonstrates absent peristalsis, oesophageal dilatation, and distal tapering at the gastro-oesophageal junction, producing the classic bird’s beak or rat-tail appearance. An air–fluid level is often visible due to retained contents. Timed barium swallow studies are useful for assessing treatment response.
Oesophageal manometry is the gold standard diagnostic test. It reveals failure of lower oesophageal sphincter relaxation during swallowing, elevated resting sphincter pressure, and absence of coordinated peristalsis in the oesophageal body.
Endoscopy is performed primarily to exclude malignancy or structural obstruction. The mucosa often appears normal, although resistance may be felt when passing the scope through the non-relaxing sphincter, and retained food debris is commonly observed.
Biopsy is not routinely required but, if taken, may show muscular hypertrophy and absence of normal ganglion cells within the myenteric plexus.

Management and Treatment Options

There is currently no curative treatment for achalasia. Management focuses on relieving functional obstruction at the lower oesophageal sphincter and improving oesophageal emptying.
Medical therapies, such as nitrates, calcium channel blockers, or botulinum toxin injection, may provide temporary relief in selected patients but are generally limited by short duration of effect.
More definitive treatments include:

• Pneumatic balloon dilatation, which forcibly disrupts sphincter muscle fibres
• Heller myotomy, a surgical division of the lower oesophageal sphincter muscle
• Peroral endoscopic myotomy (POEM), a minimally invasive endoscopic alternative