Aetiology

The lower oesophageal sphincter regulates food passage from the oesophagus to the stomach and contains both intrinsic smooth muscle and skeletal muscle. Episodes of transient lower oesophageal sphincter relaxation are a normal phenomenon, but they occur more frequently in GORD, causing reflux of gastric contents into the oesophagus.[21]​ Transient lower oesophageal sphincter relaxation is more common after meals and is stimulated by fat in the duodenum.[22]​ It is more likely to occur if there is a hiatal sac containing acid. Patients with severe reflux often have a hiatus hernia and decreased resting lower oesophageal sphincter pressure. However, pressure can be high at the lower oesophageal sphincter in some patients with mild to moderate reflux.[23]

Pathophysiology

The severity of mucosal damage depends on the duration of contact with gastric contents, characteristics of the gastric contents (acid, pepsin, and bile salts are damaging to the mucosa), and resistance of the epithelium to damage.

The duration of contact with gastric contents depends on the number of episodes of reflux, the efficacy of oesophageal peristalsis, and the neutralisation of acid by saliva.[3] Low-amplitude oesophageal contractions can occur in severe reflux, reducing the ability to clear acid from the oesophagus.

Laryngo-pharyngeal symptoms may be caused by intermittent pharyngeal reflux. This occurs mostly at night, when the upper oesophageal sphincter resting tone is reduced. Vagal stimulation (caused by acid in the lower oesophagus) may cause chronic coughing and throat clearing. Definitive evidence for these mechanisms is lacking.[24]

Reflux-induced asthma may be caused by chronic aspiration of reflux contents and vasovagal bronchoconstriction, but a clear causal relation has not yet been established. Asymptomatic gastro-oesophageal reflux is common among patients with poorly controlled asthma, but treatment with proton-pump inhibitors has not been shown to improve asthma control.[25] Symptomatic GORD in patients with asthma should be treated.[26]

Symptoms such as heartburn, regurgitation, or dysphagia may persist despite therapy with proton-pump inhibitors and remain unexplained by endoscopy, manometry, or acid monitoring. The reason is not clear. Hypersensitivity and functional syndromes have been implicated.[3]

Classification

Montreal definition[2]

This classifies oesophageal syndromes.

  1. Syndromes with symptoms and no injury:

    • Typical reflux syndrome

    • Reflux chest pain syndrome.

  2. Syndromes with oesophageal injury:

    • Reflux oesophagitis

    • Reflux stricture

    • Barrett's oesophagus

    • Oesophageal adenocarcinoma.

Extra-oesophageal syndromes

  1. Established associations:

    • Reflux cough syndrome

    • Reflux laryngitis syndrome

    • Reflux asthma syndrome

    • Reflux dental erosion syndrome.

  2. Proposed associations:

    • Pharyngitis

    • Sinusitis

    • Idiopathic pulmonary fibrosis

    • Recurrent otitis media.

Some researchers suggest that the concept of GORD as a composite, symptom-based entity requires re-evaluation.[8]

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