Pathology of the Week – Croup

medicalese: Scotch physician Dr. Francis Home first referred to croup in 1765; probably derived from the anglo-saxon word “kropan” (to cry).

Croup is a common and relatively benign condition in children. It is caused by an inflammation of the upper respiratory tract secondary to viral infection. It occurs almost exclusively in children, aged 6mo to 3y. The disease is more common in boys than girls (about 1.4:1). I will reference the Merck page on Croup, a few subscription-based articles (i.e. Bjornson et al., 2008) as well as a great free public access article by Malhotra & Krilov, 2001.

Signs and Symptoms

The hallmark symptoms of croup are a distinct “bark-like” cough and inspiratory stridor.

Children may become pyrexic (as high as 40°C). The symptom onset is usually abrupt and occurs more often during the night leading to parental discovery in the early morning hours. Although these symptoms usually disappear on their own after 48h it is important to remember this can be a terrifying experience for parents.

Differential Diagnosis

When considering a paediatric patient with acute respiratory distress there are a few alternate diagnoses to consider.

  1. Acute epiglottitis is a critical concern. A child with epiglottis will lack the hallmark barking cough and present with additional symptoms uncommon with croup such as drooling and dysphagia (difficulty swallowing). They will also prefer to sit upright in the sniffing position whereas the patient with croup will commonly be comfortable supine. Epiglottis is becoming increasingly rare in North America though, due to widespread immunisation against H influenzae after 1990.
  2. Bacterial tracheitis would present with similar upper respiratory tract Sx but with a more rapid onset as well as a more “toxic” appearance and pain while swallowing.
  3. A foreign body in the airway may cause respiratory distress as well as the bark cough. Importantly, fever and other symptoms of respiratory tract infection would be absent. There was one case of a 20mo girl in Turkey who was incorrectly diagnosed with croup. For over a year she received various treatments until a laryngoscopy revealed a small piece of plastic partially occluding her airway Atmaca et al., 2009 (free public access).

Aetiology

The symptoms of croup are caused by inflammation of the upper respiratory tract. This inflammation is part of the normal immune response to a viral infection. The virus is most commonly one of two variants of parainfluenza. The barking cough and inspiratory stridor arise because the inflammation occurs within the physical constraints of the tracheal cartilage rings. Inflammation is thus forced inwards which actually presents on an X-ray in a “steeple” shape.

Management and Treatment

In 60% of North American cases symptoms resolve on their own after 48h. One study estimated the annual mortality rate at just 1 in 30,000 cases (Bjornson et. al, 2008). Pharmacology treatments are commonly epinephrine administered through a nebulizing mask. Note this produces only transient symptomatic improvement (usually less than 2h). Another is the steroidal treatment dexamethasone (Baycadron, Dexasone, etc.), shown to benefit the patient during the acute phase of the illness. Antibiotics are rarely indicated. The common “at-home remedy” of carrying the child through a humidified environment, such as within a bathroom with the shower running, has proven no benefit beyond placebo controls (Bjornson et. al, 2008).

Implications for Prehospital Care

As croup is predominantly a disease of the upper airway tract, alveolar gas exchange is rarely compromised (Malhotra et al, 2001). It is important to remember the experience of discovering a child, seemingly, breathless and in discomfort can be a terrifying experience for parents. Calming the parents is not only important for their sake but also for the child’s. Although kind and gently patient care with young children is always paramount the demand is even higher with croup. It is especially important not to antagonize and/or scare the patient as crying will put much higher demands on their already stenotic airway. Allow the child to remain in their parent’s lap and take extra precautions to startle them as little as possible.

Bjornson et al (2008) found no evidence in support of supplemental O2 but indicated many standards of practice call for it. They suggested, in keeping with the above importance of not scaring the child, to utilize a blow-by technique. For supplemental oxygen alone forego the delivery device (mask, cannula) and present just the delivery tube on high-flow (10lpm).

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