Definition of "Croup"

Last modified: over 2 years



Croup (from English "croup" meaning "to cry hoarsely", aka laryngotracheobronchitis) is a respiratory condition triggered by an acute viral infection of the upper airway.

Sx
  • Because of common viral causes to other URTI's, it may preceed with infection of the upper airways, slowly working down the airway
  • Flu-like Sx (fever, coryza)
  • Due to laryngitis:
    • Hoarseness of voice
    • Classical "barking" cough, resembling the call of a seal or sea line
  • Due to tracheitis:
    • Stridor, worsened by agitation or crying. If heard at rest, may indicate critical narrowing of the airways
    • SOB, usually worse at night
    • Chest wall indrawing/retraction
    • Decreased air entry
    • Decreased LOC
    • Cyanosis

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Patient information

Another name for croup is laryngo-tracheo-bronchitis. So is this laryngitis + tracheitis + bronchitis?
Yes, the pharynx is at the top, then going down, is the larynx - also known as the "voice box", and then the trachea.

So if you get croup, you're going to get a combination of these 3 infections?
Yes . First, because it's a viral infection, it'll look like a flu - so fever and cough. So starting up at the top, from laryngitis you'll get hoarseness of voice. From tracheitis you'll get stridor which is like a wheeze but is lower pitch because it occurs in the upper airways. And because there's an obstruction, you'll also get shortness of breath, and increased effort to breath.

But isn't bronchitis wheeze and chest discomfort? Why don't we see that?
That's correct. Usually croup doesn't work it's way down that far. So although it's technically has the "bronchitis" part, the worst we usually see is stridor - and not wheeze. But if it works it's way down far enough - yes, we can see wheeze!

Pathophysiology
  • Infection causes swelling of the larynx, trachea and large bronchi, due to infiltration of WBC's
  • Croup doesn't infect those >6yo, because it has a wider diameter in those who are older, and thus swelling doesn't cause the same complicating effect
  • Infection can either be:
    • Viral croup (aka acute laryngotracheitis), of which spasmodic croup is caused by the same group of viruses, but lacks the usual signs of infection (e.g. fever, sore throat, increased WBC), but Tx is similar. It is caused by:
      • Parainfluenza virus, in 75% of cases
      • Influenza
      • Measles
      • Adenovirus
      • RSV 
    • Bacterial croup, which includes:
      • Laryngeal diphtheria, usually due to Corynebacterium diphtheriae
      • Bacterial tracheitislaryngotracheobronchitis, and laryngotracheobronchopneumonitis, usually due to a primary viral infection w/ secondary bacterial growth. Most common bacteria implicated are Staphylococcus aureusStreptococcus pneumoniaeHemophilus influenzae, and Moraxella catarrhalis
  • Swelling produces airway obstruction which causes dramatically increased WOB, and stridor (turbulent, noisy airflow)

Patient information

What's croup caused by?
An infection. Usually viral. Usually parainfluenza virus.

I know that croup, because it is also called laryngo-tracheo-bronchitis, is an inflammation of the larynx, trachea and bronchi. But... why does this occur in JUST kids up to 6yo? Why not adults?
It's because of the size of the airways. The main issue with croup is the swelling. That's causing all the problems. But as you grow, so does the size of your airways. They get wider. And once they are wide enough, it's going to be less effected by swelling !

Dx
  • Sx, once potentially more severe causes of Sx have been excluded (i.e. epiglotittis, or foreign body)
  • Exclude other obstructive conditions of the upper airway, especially:
    • Epiglottitis
    • Foreign body
    • Subglottic stenosis
    • Angioedema
    • Retropharyngeal abscess
    • Bacterial tracheitis
Ix

Further Ix not usually needed, as they may cause unnecessary agitation and worsen the stress on the compromised airway

  • Frontal x-ray of the neck, amy show characteristic narrowing of the trachea (called the steeple sign), because of the subglottic stenosis
  • Viral cultures via nasopharyngeal aspiratino, can confirm exact cause, but usually restricted to research settings
  • Bacterial infection should be considered if it doens't improve w/ standard Tx, thereby warranting further Ix
Tx
  • Prevention, w/ immunization for:
    • Influenza
    • Diphtheria → Before vaccination, croup was frequently caused by diphtheria, and was often fatal
  • ABC's, including oxygenation if <92%
  • Single dose of oral corticosteroids (e.g. dexamethasone, or budesonide), improves croup of all severities. Significant relief is obtained as early as 6 hours after administration
  • Inhaled adrenaline, occasionally, in more severe cases. It provides reduction in severity within 20 minutes, but only lasts 2 hours
  • Insufficient evidence, for inhalation of humidified air. Cough medicine is discouraged. Abx is not useful against a viral infection, unless secondary bacterial infection is potential
  • Hospitalization rarely required
Complications

Uncommon, but includes:

  • Bacterial tracheitis
  • Pneumonia
  • Pulmonary edema
  • Rarely results in death from respiratory/cardiac failure
Prognosis
  • Usually self-limiting, 50% going away in 1 day, and 80% in 2 days, but can last up to 7 days
  • If the condition remains improved 3 hours after Tx and no other complications arise, the child is typically discharged from hospital
Epidemiology
  • It is a relatively common condition that affects about 15% of kids at some point, usually between 6mo-6yo
  • Accounts for 5% of hospital admissions in kids 6mo-6yo
  • 3% of kids with croup will be hospitalized
  • In rare cases, it can occur in the extremities of 3mo-15yo
  • It is almost never seen in teens or adults
  • Males are affected 50% more frequent than females
  • It is more prevalent in autumn
  • "Croup" was in classical English (1500's) used very similarly to the word "croak", describing a hoarse cry
See also

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