Epiglottitis overview

# Overview
Epiglottitis is a soft tissue swelling of the epiglottis, and the surrounding structures example; plica aryepiglottica , arytenoids, sinus piriformis and vestibular folds mostly caused by bacteria. The epiglottis is  a flap of tissue at the base of the tongue that prevents food from going into the trachea. Due to its place in the airway, swelling of the epiglottis may interfere with breathing and constitutes a medical emergency, especially when it obstructs or completely closes off the windpipe.

# Historical perspective
One remarkable incidence of epiglottitis has been traced to George Washington; the first president of the United States on December 13, 1799. He was reported to have had sore throat and hoarseness of voice. At dawn the next day, his conditioned worsened with difficulty in breathing. Few hours later he was found to have respiratory distress and died few hours later of what was known to be due to acute epiglottitis.  In the 1980s Haemophilus influenza type b vaccine was introduced. Prior to this,  epiglottitis used to be mostly found in pediatric age group between 3 to 5 years. However, recent trend in North America favors adults as most commonly affected individuals.

# Classification
Epiglottitis may be classified according to the etiology, and disease duration into infectious and noninfectious causes. Infectious epiglottitis may be subclassified into bacterial, viral and fungal causes.
Noninfectious epiglottitis is main due to trauma from foreign objects inhalation and chemical burns On the basis of disease duration, epiglottitis is almost always acute in presentation requiring emergency treatment else the outcome is fatal.

# Pathophysiology
Understading the pathogenesis of epiglottitis involves a good knowlegde of the causative organisms. 
The only known reservoirs for H. influenzae in humans include, respiratory tract, conjunctival and genital surfaces. Pathogenicity of H. influenza is as a result of imbalance between the virulent factors of the organism and the host immune system. This immunity is enhanced when children are vaccinated with the purified polyribosylribitol phosphate (PRP). H. influenza type b capsule is antiphagocytic. Serum anit-purified polyribosylribitol phosphate (anti-PRP) antibody is important in the complement dependent phagocytosis and lyses of the bacteria.  IgA antibody accords the mucosa surface protection again attachment of the organism. The strategies deployed by a microbe to assist its survival and proliferation,  may or may not lead to disease process.  Epiglottitis caused by H. influenza may therefore be considered as an accidental consequence of the microbial factors that permit its survival. Acute epiglottitis pathogenesis is well exemplified by H. influenzae, with the ability to colonize mucosal surfaces and to spread contiguously or invade epithelial cells. It commonly disseminates within the bloodstream, or localizes to selected tissues among these is the epiglottis.  Microbial invasion of the bloodstream around the epiglottis leads to inflammatory response and tissue edema most apparent at the lingual surface of the epiglottis compared to the laryngeal surface. The extravasation of fluid leads to remarkable tissue swelling that may lead to respiratory obstruction and the other symptoms of epiglottitis. The pathogenesis of necrotizing epiglottitis involves the infection with CMV or EBV usually in immunocompromised people. Affected patients are usually neutropenic and lymphopenic at presentation. CMV and EBV modulate the host's immune defense facilitating immune evasion and thereby predisposing the patient to a superimposed infections.
The causative organism of necrotizing epiglottitis is unclear.

# Causes
Prior to the introduction of Haemophilus influenza type b vaccine, H. influenza was the most common culprit of epiglottitis. In recent literature, group A -hemolytic Streptococci is more commonly observed to be the cause. The disease used to be mostly found in pediatric age group of 3 to 5 years. However, recent trend favors adults as most commonly affected individuals. Other pathogens such as escherichia coli, candida albicans, or kingella kingae may be encountered in immunocompromised hosts. Occasionally, noninfectious causes examples trauma from foreign objects inhalation and chemical burns have been found to cause epiglottitis.

# Differentiating epiglottitis from other diseases
Epiglottitis must be differentiated from other upper respiratory diseases and conditions that may cause throat pain and airway obstruction examples: Croup (Laryngotracheobronchitis), Foreign body obstruction, Subglottic stenosis, pharyngitis, Tonsilitis, Angioedema, uvulitis, retropharyngeal or peritonsilar abscesses and Bacterial tracheitis. For example, although patients with croup and epiglottitis both have stridor, in epiglottitis there is associated drooling without a cough whereas in croup there is cough but no drooling.

# Epidemiology and demographics
In North America, approximatley 1.3 per 100,000 children are affected per year. In adults, the incidence is between 1 and 4 per 100,000 per year. December is observed to be the month with highest number of cases whilst April is the least. Males are more commonly affected with epiglottitis in USA than females. The male to female ratio is approximately 3:2.  The disease used to be mostly found in pediatric age group between 3 to 5 years. However, recent trend favors adults as most commonly affected individuals with a mean age of 44.94 years. Recent data suggest an increase in those between 45 to 64 years old as well as those over 85 years whilest those below 18 years is decreasing. In USA, epiglottitis is more prevalent in the caucasian race in urban communities accounting for over 2/3rd of all epiglottitis admissions. Epiglottitis occurs more commonly in developing countries.

# Screening
There is no screening modality available for epiglottitis.

# Risk factors
Risk factors in the development of epiglottitis include the absence of immunization, immunocompromised state, smoking, and postsplenectomy.

# Natural history, complication and prognosis
Epiglottitis if left untreated may result in respiratory obstruction and death within few hours. Acute epiglottitis may be complicated by the following: epiglottic abscess, emphysematous epiglottitis, septic epiglottic chondritis with or without abscessation, airway obstruction and pneumonia. With appropriate and timely diagnosis and treatment, the prognosis is usually good.

# Diagnosis

## History and symptoms
Epiglottitis presents differently in children and adults. 80 to 95% of adults with epiglottitis present with sore throat and dysphagia  whereas the predominant symptoms in infected children are high fever, muffled or hoarse voice, drooling and difficulty swallowing.  A forward-leaning position with drooling while trying to breathe is typically seen in affected children. The child often appears acutely ill, anxious, and has very quiet and shallow breathing with the head held forward, on insisting on sitting up in bed. Adults usually have milder presentations and less commonly develop airway obstruction with respiratory distress. Other common symptoms may include: abnormal breathing sounds (stridor), chills, rigor, cyanosis, and Difficulty breathing

## Physical examination
A definitive diagnosis of acute epiglottitis can be confirmed by direct inspection under laryngoscopy, although this may provoke airway obstruction. The epiglottis and the surrounding structures appear erythematous and swollen. Physical examination may include: tenderness of anterior neck, high temperature, increased respiratory rate in both children and adults, pharyngeal redness and cervical lymphadenopathy. In addition, patients with epiglottitis may adapt the so called tripod posture with hyper-extension of the neck, chin pointing forward and trunk and arms leaning forward.

## Laboratory findings
Although there is no specific laboratory test for epiglottitis, the following nonspecific test are helpful. These include blood culture, complete blood count, arterial blood gases and throat culture. Throat culture should only be done in intubated patients.

## Xray
On lateral soft tissue X-ray of the neck, the thumbprint sign a finding that suggests the diagnosis of epiglottitis is seen.
The thumbprint sign is a manifestation of swollen and edematous epiglottis. This shows as a hemispherical mass at the base of the tongue replacing the normal slender coma shape of the epiglottis.

## ECG
There is no ECG finding in epiglottitis.

## CT scan
Computed tomography of the neck in epiglottitis shows swelling and edema of the epiglottis at the base of the tongue.

## MRI
MRI in a patient with epiglottitis shows thickening of the epiglottis and aryepiglottic fold. However, it is unnecessary to do imaging in this life-threatening condition unless the diagnosis is uncertain or when an abscess or other complication is suspected.

## Ultrasound
The bedside ultrasonography is a safe and noninvasive study that is very useful in evaluating a patient in the emergency department when acute epiglottitis is suspected. The alphabet "P" sign is formed by acoustic shadow of hyoid bone and swollen epiglottis at the level of thyrohyoid membrane in a longitudinal orientation.

## Other imaging findings
There are no other imaging findings of epiglottitis.

## Other diagnostic findings
Other diagnostic studies involve the use of fibreoptic laryngoscope which shows the omega sign. This refers to the thickened aryepiglottic folds and epiglottis observed in epiglottitis, when the larynx is seen endoscopically or via laryngoscope as shown below.

# Treatment

## Medical therapy
Epiglottitis is a medical emergency and warrants immediate establishment of a patent airway. Once the airway has been secured, cultures of blood and epiglottic surface should be obtained before administration of antimicrobial therapy. Administering high-flow oxygen, establishing intravenous access, and calling an ENT specialist are standard first-line interventions for epiglottitis.  An appropriate antibiotic regimen that covers Streptococcus pneumoniae, beta-hemolytic streptococci, and Staphylococcus aureus includes parenteral Cefotaxime or Ceftriaxone in combination with Vancomycin (or Levofloxacin in combination with Clindamycin for Penicillin-allergic patients).  Adjuvant therapy is commonly used in the management of stridor associated with acute epiglottitis.
Adjuvant therapy includes corticosteroids and racemic Epinephrine.

## Surgery

### Surgery and Device Based Therapy
Epiglottitis requires urgent endotracheal intubation to protect the airway. Ideally, this should be performed in the theater by an experienced anesthesiologist or respiratory therapist, with otolaryngologist back-up in case of failed intubation. If intubation fails, tracheotomy is required.

# Prevention
Immunization with the Hib vaccine protects children from epiglottitis. Postexposure prophylaxis with rifampin should be given to selected household contacts when a Haemophilus influenzae epiglottitis is diagnosed. In the United states, vaccination against Hib in children  was initiated in the 1980s. Immunity against Hib has been adequate with an increasing level of immunization among children. Post-splenectomy patients are also recommended to be immunized.