Dysphagia can arise at the oropharyngeal level or the esophageal level, and the two differ in how they present and in what causes them.
Oral and pharyngeal (oropharyngeal) dysphagia
Oropharyngeal dysphagia is trouble starting a swallow or moving the bolus through the mouth and pharynx. When the oral phase fails, the bolus is retained in the mouth for longer, saliva may drool, initiating a swallow becomes difficult, and food may seep back out of the mouth. When the pharyngeal phase fails, food is retained in the pharynx and may be aspirated into the airway.
The pharyngeal phase fails for three main reasons: the tongue cannot propel the bolus, the pharyngeal muscles cannot drive it onward, or the UES is obstructed or fails to open. The causes group along those lines. Neurological disease damages the control of swallowing and is common — cerebrovascular accidents, Parkinson’s disease and amyotrophic lateral sclerosis are the classic examples. Muscular disease weakens the swallowing muscles themselves. Structural lesions such as a cricopharyngeus bar, a Zenker’s diverticulum or a neoplasm block the passage. Head and neck cancer surgery or radiation can leave iatrogenic scarring. Infections and metabolic causes also interfere with neuromuscular control.
Because the pharyngeal phase is fast — it normally lasts less than 1 second — it cannot be judged by history and examination alone, and fluoroscopic examination is needed to examine it.
Esophageal dysphagia
Esophageal dysphagia is the feeling that food is stuck after it has left the pharynx, and it usually appears when the lumen is narrowed. Solid-food dysphagia typically begins once the internal diameter of the esophagus is reduced to less than 13 mm, which is why solids are affected before liquids. A lesion that narrows the whole circumference (a circumferential mass) causes dysphagia far more often than one that occupies only part of the circumference.
The most common causes of esophageal dysphagia are Schatzki’s ring, eosinophilic esophagitis and peptic strictures. These are three ways of narrowing the lumen: a mucosal ring at the gastroesophageal junction, eosinophil-driven inflammation and fibrosis, and acid-driven scarring.
Dysphagia from a motility disorder behaves differently: it tends to affect solids and liquids equally, and the classic example is achalasia, the failure of the lower esophageal sphincter (LES) to relax together with loss of esophageal peristalsis. Dysphagia can also occur in GERD, probably because the esophagus becomes less sensitive to distension rather than only because of narrowing. In scleroderma, absent contractility of the esophageal body combines with severe weakness of the LES, so transport fails for a propulsive rather than a structural reason.