Croup, or laryngotracheobronchitis, is the most common infection of the middle respiratory tract (Table 107-1). The most common causes of croup are parainfluenza viruses (types 1, 2, 3, and 4) and respiratory syncytial virus. Laryngotracheal airway inflammation disproportionately affects children because a small decrease in diameter secondary to mucosal edema and inflammation exponentially increases airway resistance and the work of breathing. During inspiration, the walls of the subglottic space are drawn together, aggravating the obstruction and producing the stridor characteristic of croup. Croup is most common in children 6 months to 3 years of age, with a peak in fall and early winter. It typically follows a common cold. Symptomatic reinfection is common, yet reinfections are usually mild. In adolescents, it manifests as laryngitis.
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The manifestations of croup are a harsh cough described as barking or brassy, hoarseness, inspiratory stridor, low-grade fever, and respiratory distress that may develop slowly or quickly. Stridor is a harsh, high-pitched respiratory sound produced by turbulent airflow. It is usually inspiratory, but it may be biphasic and is a sign of upper airway obstruction. Signs of upper airway obstruction, such as labored breathing and marked suprasternal, intercostal, and subcostal retractions, may be evident on examination (see Chapter 135). Wheezing may be present if there is associated lower airway involvement.
Anteroposterior radiographs of the neck often show the diagnostic subglottic narrowing of croup known as the steeple sign (Fig. 107-1). Routine laboratory studies are not useful in establishing the diagnosis. Leukocytosis is uncommon and suggests epiglottitis or bacterial tracheitis. Many rapid tests (using polymerase chain reaction or fluorescent antibodies) are available for parainfluenza viruses, respiratory syncytial virus, and other less common viral causes of croup, such as influenza and adenoviruses.
The diagnosis of croup usually is established by clinical manifestations. The infectious differential diagnosis includes epiglottitis, bacterial tracheitis, and parapharyngeal abscess. Noninfectious causes of stridor include mechanical and anatomic causes (foreign body aspiration, laryngomalacia, subglottic stenosis, hemangioma, vascular ring, vocal cord paralysis). Stridor in infants younger than 4 months of age or persistence of symptoms for longer than 1 week indicates an increased probability of another lesion and the need for imaging and direct laryngoscopy (see Chapter 135).
Epiglottitis is a medical emergency because of the risk of sudden airway obstruction. This illness is now rare and usually caused by group A streptococcus or Staphylococcus aureus or Haemophilus influenza type b in unimmunized patients. Patients typically prefer sitting, often with the head held forward, the mouth open, and the jaw thrust forward (sniffing position). Lateral radiograph reveals thickened and bulging epiglottis (thumb sign) and swelling of the aryepiglottic folds. The diagnosis is confirmed by direct observation of the inflamed and swollen supraglottic structures and swollen, cherry-red epiglottitis, which should be performed only in the operating room with an anesthesiologist and a competent surgeon prepared to place an endotracheal tube or perform a tracheostomy if needed. Epiglottitis requires antibiotic therapy and endotracheal intubation to maintain the airway. Clinical recovery is rapid, and most children can be extubated safely within 48 to 72 hours.