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Background
The term "hiccup" derives from the sound of the event. "Hiccough" erroneously implies an association with respiratory reflexes. The medical term, singultus, is thought to have originated from the Latin, singult, which translates roughly as "the act of catching one's breath while sobbing."
Brief episodes of hiccups, which often induce annoyance in patients and merriment in observers, are a common part of life. Prolonged attacks are a more serious phenomenon and often a diagnostic dilemma. These attacks have been associated with significant morbidity and even death.
A hiccup bout is any episode lasting more than a few minutes. If hiccups last longer than 48 hours, they are considered persistent or protracted. Hiccups lasting longer than one month are termed intractable. The longest recorded attack is 6 decades.
Pathophysiology
Hiccups appear to serve no purpose in humans or other mammals. Often, only one hemidiaphragm is affected. The left hemidiaphragm is affected in 80% of cases, although bilateral involvement may occur.
Hiccups occur 4-60 times per minute until a certain number has been delivered. Typically, this is fewer than 4 or more than 30. The frequency is relatively constant for a given individual and varies inversely with arterial PCO2. Loudness and rapidity of hiccups are unrelated. Hiccups are more common in the evening and may continue for a few waking hours. Hiccups occur most frequently during the first half of the menstrual cycle, especially in the few days before menstruation, and decrease markedly during pregnancy.
The exact cause remains a mystery despite centuries of contemplation. Hippocrates and Celsus associated hiccups with liver inflammation and other conditions. Galen believed hiccups were due to violent emotions arousing the stomach.
In 1833, Shortt first recognized an association between hiccups and phrenic nerve irritation.
The hiccup reflex, originally proposed by Bailey in 1943, consists of the following:
•Afferent limb - Phrenic and vagus nerves and sympathetic chain arising from T6-12
•Hiccup center - Nonspecific location between C3 and C5
•Connections to the respiratory center, phrenic nerve nuclei, medullary reticular formation, and hypothalamus
•Efferents
◦Phrenic nerve (C3-5)
◦Anterior scalene muscles (C5-7)
◦External intercostals (T1-11)
◦Glottis (recurrent laryngeal component of vagus)
◦Inhibitory autonomic processes
◦Decreasing esophageal contraction tone
◦Lower esophageal sphincter tone
Sex
Overall incidence of hiccups is equal between males and females; however, protracted and intractable hiccups occur more frequently in men (82% of cases).
Age
Hiccups occur at any age and in utero. Preterm infants spend up to 2.5% of their time hiccupping. Although hiccups occur less frequently with advancing age, intractable hiccups are more common in adult life. Females develop hiccups more frequently during early adulthood than males of the same age.
Clinical
History
Medical training is not required to diagnose hiccups. Brief episodes that self-terminate or that respond to simple maneuvers need no investigation or follow-up care.
In contrast, persistent and intractable hiccups frequently are associated with an underlying pathological process and may induce significant morbidity. The focus of the history, examination, and investigation is to identify these causes and effects.
•Hiccups that abate with sleep and temporally relate to stressful circumstances commonly are psychogenic in origin.
•Arrhythmia-induced syncope has been reported as both the cause and the effect of hiccups.
•Gastroesophageal reflux may cause or result from hiccups.
•Weight loss, insomnia, and emotional distress may complicate prolonged episodes.
•A full systemic inquiry, surgical history, and comprehensive drug history may reveal one of the many causes (see Causes).
•Alcoholism and acute alcohol ingestion may contribute to the development of hiccups.
Physical
A full physical examination is necessary. Considering the wide range of differentials, a complete and focused physical examination may yield evidence of the following:
•Head - Including ears, eyes, entire scalp
◦Foreign body or aberrant hair adjacent to tympanic membrane
◦Glaucoma
•Mouth -Pharyngitis
•Neck
◦Inflammation (including laryngitis)
◦Mass lesions
◦Goiter
◦Voice abnormalities (recurrent laryngeal nerve)
•Chest
◦Tumors
◦Pneumonia
◦Asthma
•Cardiovascular
◦Arrhythmias
◦Myocardial infarction (MI)
◦Pericarditis
◦Unequal pulses -Thoracic aortic aneurysm
•Abdominal
◦Gastric atony - Succussion splash
◦Organomegaly
◦Subphrenic abscess
◦Cholecystitis
◦Appendicitis
◦Abdominal aortic aneurysm (AAA)
◦Pancreatitis
◦Peritonitis
•Rectal - Mass lesions
•Neurologic
◦Focal lesions
◦Disordered higher mental function
◦Indications of multiple sclerosis
•Neck stiffness - Possible indication of tumors or infection
Causes
The cause of hiccups in children and infants is rarely found. Brief episodes in adults are usually benign and self-limiting.
Typical causes include gastric distention (ie, food, alcohol, air), sudden changes in ambient or gastric temperature, and use of alcohol and/or tobacco in excess. Psychogenic causes (ie, excitement, stress) also may elicit hiccups.
Persistent or intractable episodes are more likely to result from serious pathophysiological processes affecting a component of the hiccup reflex mechanism. More than 100 causes have been described; however, in many cases, the cause remains idiopathic. These may be classified as follows:
•Eighty-two percent of persistent or intractable episodes occur in men. An organic cause can be identified in 93% of men and in 8% of women, resulting in an overall organic incidence of 80%. The remaining 20% are considered psychogenic in origin.
◦Hysteria
◦Shock
◦Fear
◦Personality disorders
◦Conversion disorders
◦Malingering
•Central nervous system
◦Structural1 - Congenital malformations, malignancies, multiple sclerosis
◦Vascular lesions
◦Infection
◦Trauma
•Diaphragmatic irritation
◦MI
◦Pericarditis
◦Hiatal hernia
◦Subphrenic abscess
•Vagus nerve irritation
◦Meningeal branches - Meningitis, glaucoma
◦Auricular branches - Foreign body, hairs
◦Pharyngeal branches - Pharyngitis
◦Recurrent laryngeal nerve - Mass lesions in neck, goiter, laryngitis2 ◦Thoracic branches - Infection, tumors, esophagitis (ie, reflux), MI, asthma, trauma, thoracic aortic aneurysm
◦Abdominal branches - Tumors, gastric distension, peptic ulcer, AAA, infection, organ enlargement, inflammation (eg, appendicitis, cholecystitis, inflammatory bowel disease)
•Procedure/anesthesia related3,4 ◦Hyperextension of neck - Stretching phrenic nerve roots
◦Manipulation of diaphragm or stomach
◦Laparotomy
◦Thoracotomy
◦Craniotomy
•Metabolic
◦Hyponatremia
◦Hypokalemia
◦Hypocalcemia
◦Hyperglycemia
◦Uremia
◦Hypocarbia
◦Fever
•Drugs
◦Benzodiazepines
◦Short-acting barbiturates
◦Dexamethasone
◦Alpha methyldopa
