Just as there are two types of dysphagia – oropharyngeal and esophageal dysphagia – there are similarly two broad groups of causes for dysphagia. Within each broad group, there are two subgroups of causes: neuromuscular (involving the nerve or muscle), and structural, where the esophagus is narrowed or compromised.
Oropharyngeal dysphagia: Neuromuscular causes are more frequent than structural causes for this type of dysphagia. This is because the nerves controlling the muscles of the mouth, back of throat (pharynx) and top end of the esophagus (upper esophageal sphincter) have direct connections with the brain through cranial nerves, and can therefore be damaged in diseases involving the brain or cranial nerves.
Less common than neuromuscular causes are structural causes, including strictures (narrowed areas), or rarely tumors growing in the back of the throat.
Esophageal dysphagia: In this type of dysphagia, structural causes are far more frequent than disorders involving nerves or muscles. Therefore, narrowing in the esophagus from scarring due to acid reflux disease, inflammation of the lining of the esophagus (usually from acid reflux disease but occasionally from infections), tumors within the esophagus, and compression of the esophagus from growths in the chest or sometimes even an enlarged heart can all cause dysphagia. In addition, a unique type of inflammation caused by a type of blood cell called eosinophils can cause dysphagia; this condition is called eosinophilic esophagitis.
Less common are disorders involving the nerves and muscle of the esophagus. The esophageal muscle can be weak and sometimes unable to generate adequate pressure during contraction. In extreme situations, the muscle generates no force and is unable to squeeze – this is sometimes called scleroderma esophagus (even though scleroderma is not frequently the cause), and can be associated with dysphagia. Another disorder of the nerves and muscles is achalasia; a condition in which the muscle at the bottom end of the esophagus cannot relax during swallowing because of abnormal nerve control. The muscle in the body of the esophagus also does not squeeze normally in achalasia, and becomes weak and stretched. When the nerves are abnormal to a lesser degree, spasm of the esophagus may result, which can also cause dysphagia.