Aphagia is the inability or refusal to swallow. The word is derived from the Ancient Greek prefix α, meaning "not" or "without," and the suffix φαγία, derived from the verb φαγεῖν, meaning "to eat." It is related to dysphagia which is difficulty swallowing (Greek prefix δυσ, dys, meaning difficult, or defective), and odynophagia, painful swallowing (from ὀδύνη, odyn(o), meaning "pain"). Aphagia may be temporary or long-term, depending on the affected organ. It is an extreme, life-threatening case of dysphagia. Depending on the cause, untreated dysphagia may develop into aphagia.
The following behavioral classifications result from studies done on rats, in which lesions were made on the lateral hypothalamus region in the brain.
- Passive aphagia: An animal with passive aphagia will not respond to food if it is presented. However, if food is inserted into the mouth, the animal will chew.
- Active aphagia: Active aphagia is a complete rejection of food. The animal will physically push food away or move its head from it. One might first sample the food by smelling or tasting, then spit out anything in the mouth. Afterwards the animal will show a complete repulsion to the food. The animal reacts to food as if it is bitter or foul.
- Mixed aphagia: When presented with food, the animal initially does not react positively or negatively. However, when food is placed in the mouth, the animal demonstrates active aphagia, spitting out the food and refusing to eat thereafter.
These studies point to the function of the hypothalamus in regulating food intake. Animals in this study also demonstrated several other types of eating behavior: "weak eating," in which the animal slowly approaches, chews, and swallows small observable amounts of food for a brief period; "good eating," in which the animal reaches normally for the food and eats reliably; and "vigorous eating," in which the animal gluttonously reaches for and devours the food. In these cases, there was either minor or no damage to the lateral hypothalamus.
Aphagia not classified under behavioral aphagia typically has a structural cause, see causes.
Aphagia is usually the result of many different diseases as well as different medical treatments. The most common things that can lead to aphagia are:
- Esophageal cancer - there are two types of esophageal cancer. The squamous cell cancer from the squamous cells of the tongue or the adenocarcinoma from glandular cells present at the junction of the esophagus and stomach. This leads to a local tumor growth with spreading later. This spreading may lead to larger tumors that would result in the inability to swallow.
- Esophageal webs - thin membranes located in the esophagus. Abnormalities can cause constrictions within the esophagus.
- Myasthenia gravis - the thymus gland is thought to be necessary for the deletion of auto-reactive T cells, and seems to have an important role in the pathogenesis of myasthenia gravis. In patients the thymus is typically enlarged, and contains many germinal centers with T and B cell areas very similar to those seen in lymph nodes. The tumour in thymoma associated disease is typically epithelial in nature. 
- Facioscapulohumeral muscular dystrophy - even though there is not a clear correlation between the facioscapulohumeral muscular dystrophy and the pharyngeal and upper esophageal striated muscle. Minor, and nonspeciﬁc, primary esophageal dysmotility was present as seen in the 2008 study by Joerg-patrick Stübgen. 
- Chemotherapy - radiation from cancer therapy may cause a stricture of the throat leading to the inability to swallow.
- Stroke - swallowing problems can cause stroke victims to aspirate food or liquid into the lungs and cause pneumonia mostly in elderly people.
- Parkinson's disease - the mechanism of swallowing disorders in Parkinson's disease may be related to extrapyramidal and autonomic system disorders. The cardinal symptoms of Parkinson's disease: tremor, bradykinesia, and rigidity are initially responsible for swallowing, which is mainly observed in the advanced stages of the disease
- Damage to the lateral hypothalamus can also lead to aphagia, as seen in the 1978 study by Timothy Schallert and Ian Whishaw.
- Other causes might be due to depression, cervical spine disease and conversation disorders.
It is important to note that all this causes (except due to the damage of the lateral hypothalamus) are indirect causes of aphagia.
- Barium swallow - videofluroscopic swallow (fluroscopy). A lateral video X-ray that provides objective information on bolus transport, safest consistency of bolus, and possible head positioning and maneuvers that may facilitate swallow function depending on each individual's anatomy and physiology.
- Esophagogastroduodenoscopy - a diagnostic endoscopic procedure that visualizes the upper part of the gastrointestinal tract.
- Esophageal motility study - a test to assess motor function of the upper and lower esophageal sphincter as well as the esophageal body.
- Maintaining nutrition and hydration - A dry mouth can make aphagia worse. This is because you may not have enough saliva to help move food out of your mouth and through your esophagus. A dry mouth can be caused by medicines or another health problem.
- Eating slowly and chewing thoroughly
- Changing the diet to softer foods or pureeing solid foods
- Feeding tubes - may be used to supplement nutrition and bypass the area where the swallowing difficulty lies
- Surgery - in very rare cases
- Biofeedback or compensating swallowing techniques
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