Hiccups are referred to as singultus. It is a common condition that has been experienced by everyone. Not many people know that hiccups can be associated with some serious medical conditions. Before we discuss the cause of hiccups, we have to know how a hiccup arises.
Hiccup is a sound that occurs during deep inspiration of air into the lungs and simultaneous closure of the vocal cords. This event is accompanied with spasms of diaphragm, which is the muscle tissue separating the chest from the abdomen. The diaphragm is innervated by a paired diaphragmatic nerve (phrenic nerve). Phrenic nerve has its center in the brainstem and it runs into chest near esophagus, heart and lungs into the diaphragm. Irritation or direct damage of any part of this neural pathway can cause hiccups.
Surprise, shock and other sudden changes of emotions may influence nerve centers to provoke an attack of hiccups regardless of the nature of emotions (either positive or negative).
Stomach distension irritates the diaphragm and that usually causes hiccups. This is probably the most common cause of hiccups and it accompanies hasty eating when the stomach is stretched with higher amount of food and digested air. Gas from sparkling beverages (carbon dioxide) may add to final effect. The medical examination typically causing hiccups by stomach distension is esophagogastroduodenoscopy, in which the stomach is inflated by air to improve examination visibility.
Phrenic nerve irritation
Effect of medications and other substances
Inner environment imbalances
Disruption of inner environment of the organism may cause irritation of the central nervous system and thereby a number of symptoms including hiccups. These factors include blood ion concentrations imbalances (e.g. sodium), or accumulation of toxic products of metabolism (e.g. so-called uremic syndrome in chronic renal failure).
Intractable hiccups may follow damage to brainstem centers controlling phrenic nerve. The most common causes of such damage include ischemic or hemorrhagic stroke, local growth of a brain tumor, head injury, encephalitis or meningitis and local effects of multiple sclerosis.
We usually do not examine a person because of a short attack of hiccups, especially when it is linked to food intake. On the other hand, prolonged or even chronic hiccups should be examined by a doctor. In addition to medical history and physical examination we can do blood tests (control of inner environment including blood ions levels) and perform a neurological examination. In case there is a suspicion of central nervous system disease, it is wise to execute a computed tomography or magnetic resonance imaging of brain. Basic chest anatomy may be evaluated from simple chest X-ray that can be supplemented by computed tomography.