December 7th, 2020

What Causes Hiccups?

Many of us, if not all have experienced hiccups at some point in our lives. Even mammals and amphibians have hiccups. But have you thought of what exactly causes hiccups?

A hiccup is a sudden, involuntary spasm of the diaphragm muscle between regular breaths. The diaphragm is the dome shaped muscle under your ribcage. The diaphragm is being innervated by the phrenic nerve, which comes all the way from our neck to the lower part of the chest. Anything that irritates the phrenic nerve can then stimulate the diaphragm and cause hiccups. Normally, the diaphragm muscle helps pull air into the lungs by pulling downwards as you breathe in, acting as a piston that suctions the air into the lungs. When you breathe out, the diaphragm pushes upwards, again like a piston. When the diaphragm spasms, the lungs suck in air quickly, and the epiglottis (the valve at top of the trachea) closes abruptly. This action stops more air from getting into the lungs and produces the “hiccup” sound we are familiar with, which occurs as the the valve shuts due to the air pressure differential.

Anything that irritates the phrenic nerve can then stimulate the diaphragm and cause hiccups.
Anything that irritates the phrenic nerve can then stimulate the diaphragm and cause hiccups.

Two Types of Hiccups:

Typically, hiccups are not pathologic, and they stop on their own, but sometimes hiccups are a symptom of another disease.

Generally speaking, we can divide the causes of hiccups to two major groups: Non-Pathological and Pathological etiologies – most hiccups that we see and are accustomed to are non-pathological in nature.

Non-Pathological causes of hiccups:

Many of the non-pathological reasons for the hiccups are associated with eating and drinking, which in some circumstances can trigger the phrenic nerve. When we eat quickly, air can enter into the stomach with the food, and this can cause distention in the stomach, which in turn places mechanical pressure on the phrenic nerve, ultimately causing the hiccups.

We see this occur in nature in the same way, often with animals, such as dogs, that eat quickly. Another way that air can enter the stomach occurs when we chew gum or smoke – both conditions can cause distention of the stomach and additional pressure on the phrenic nerve. Eating spicy foods can also trigger hiccups, and in this scenario the acidity of the spice, chemically triggers the phrenic nerve, which is located close to the stomach.

Another cause of non-pathologic hiccups involves carbonated and alcoholic beverages; both of these chemically irritate the phrenic nerve, near the stomach, and that triggers hiccups.  

Pathological causes of hiccups:

Pathological hiccups are less common but can be much more serious, and should be investigated by a patient’s physician. Here are is a breakdown of those causes.

A – Neurological causes:

In this category, most of the etiologies are due to a pathology inside the brain, where the central nervous system nucleuses for phrenic and vagus nerves are located. One of the most common causes of hiccups in this group are a result of strokes – especially when the stroke has happened at the medulla. The medulla is a part of the brain stem that connects the spinal cord to the brain. Other pathological masses that press the medulla also can manifest as hiccups such as brain aneurysms, arterio-venous malformation and demyelinating diseases.

B – Gastrointestinal causes:

Another pathological etiology for hiccups occurs when the lower part of the esophagus (food pipe), nearest to the stomach, becomes irritated. In this category, the most common causes include acid-reflux, peptic ulcers and gastritis; some less common causes include esophageal or stomach cancer. But, in these cases, patients usually experience other symptoms – it’s rare that hiccups are the only manifestation.

At times the hiccups can occur after surgery and this can be multifactorial – mainly due to the location of surgery on the abdomen, the intubation for anesthesia and other forms of anesthetics used during surgery.

C – Infections and Inflammations:

Other causes of the pathological hiccups are the inflammations in the throat and chest such as pharyngitis (sore throat), pneumonia (lung infection), bronchitis ( infection of the airways), pericarditis( heart membrane inflammation) and sometimes heart attacks.

D – Medication-induced Hiccups:

Aside from other pathological conditions, sometimes hiccups can be a side effect of a medication. For example, some cancer patients who undergo chemotherapy develop hiccups as a side effect of the chemotherapy medications. Certain anti-cancer drugs (chemotherapy) such as: levofolinate, fluorouracil, oxaliplatin, carboplatin and irinotecan are associated more with hiccups.

Dexamethasone in some cases cause hiccups as well. This drug is used for various indications including brain edema and reducing chemotherapy-induced side effects. Discontinuation of dexamethasone or switching from dexamethasone to other corticosteroids have been reported to relieve hiccups.

The last class of medications that can cause hiccups are the sedatives and pain killers. Medications such as diazepam, midazolam, barbiturates and tramadol are included in this category.

E – Electrolyte and metabolic causes:

Kidney and liver malfunction can cause an accumulation of some toxins and imbalance of several electrolytes in the body. A known toxic metabolite of the body is urea, which will retain in the body when there’s kidney failure. This high urea, named uremia, can manifest as hiccups. Other electrolytes and gasses in the blood play an important role in the body’s metabolism and an imbalance of these substances can cause hiccups. Electrolytes and gas conditions such as hypokalemia (low potassium), hyponatremia (low sodium), hypocalcemia (low calcium) and hypocapnia (low carbon dioxide).

F – Psychogenic Hiccups:

Anxiety, stress, excitement, and malingering can be another trigger for the hiccups. However, psychogenic causes of hiccups should be considered only after a thorough evaluation has been completed looking for other medical causes. One way that we, as physicians, can differentiate the psychogenic hiccups from true hiccups is that they persist during sleep, but the psychogenic hiccups will only occur when awake.

Here’s a summary of possible causes:

Central nervous system causes:

  • Strokes – especially at the medulla of the brain
  • Head injures
  • Brain tumors
  • Irritation of Vagus or Phrenic nerves with impact on the Gastrointestinal system:
    • Acid Reflux
    • Gastritis
    • Peptic Ulcer
    • Gastric cancer
    • Gastric distention:
      • Eating fast
      • Swallowing air while chewing gum
      • Smoking
      • Overeating
      • Eating spicy foods
      • Drinking carbonated beverages
      • Drinking alcohol
      • Sudden changes in ambient or gastrointestinal temperature

Medication-induced:

  • Dexamethason
  • Diazepam
  • Midazolam
  • Tramadol
  • Barbiturates
  • Alpha methyldopa
  • Certain anti-cancer drugs (chemotherapy), including:
    • Levofolinate
    • fluorouracil
    • oxaliplatin
    • carboplatin
    • irinotecan

After some surgeries involving the:

  • Phrenic nerve
  • Esophagus
  • Diaphragm.

Toxic-Metabolic:

  • Uremia (kidney disease)
  • Hyponatremia (Low Sodium)
  • Hypokalemia (Low Potassium)
  • Hypocalcemia (Low Calcium)
  • Hypocapnia (Low CO2)

Psychogenic factors:

  • Anxiety
  • Stress
  • Excitement
  • Malingering