Etiology
The lower esophageal sphincter regulates food passage from the esophagus to the stomach and contains both intrinsic smooth muscle and skeletal muscle. Episodes of transient lower esophageal sphincter relaxation are a normal phenomenon, but they occur more frequently in GERD, causing reflux of gastric contents into the esophagus.[21] Transient lower esophageal 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 hiatal hernia and decreased resting lower esophageal sphincter pressure. However, pressure can be high at the lower esophageal 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 esophageal peristalsis, and the neutralization of acid by saliva.[3] Low-amplitude esophageal contractions can occur in severe reflux, reducing the ability to clear acid from the esophagus.
Laryngo-pharyngeal symptoms may be caused by intermittent pharyngeal reflux. This occurs mostly at night, when the upper esophageal sphincter resting tone is reduced. Vagal stimulation (caused by acid in the lower esophagus) 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 gastroesophageal 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 GERD 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 esophageal syndromes.
Syndromes with symptoms and no injury:
Typical reflux syndrome
Reflux chest pain syndrome.
Syndromes with esophageal injury:
Reflux esophagitis
Reflux stricture
Barrett esophagus
Esophageal adenocarcinoma.
Extraesophageal syndromes
Established associations:
Reflux cough syndrome
Reflux laryngitis syndrome
Reflux asthma syndrome
Reflux dental erosion syndrome.
Proposed associations:
Pharyngitis
Sinusitis
Idiopathic pulmonary fibrosis
Recurrent otitis media.
Some researchers suggest that the concept of GERD as a composite, symptom-based entity requires re-evaluation.[8]
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