Measles is an important cause of severe croup. Acute spasmodic croup is a similar syndrome in children who experience recurrent attacks precipitated by viral infections, allergies, or possibly other factors. The differential diagnosis includes foreign-body aspiration or trauma, bacterial epiglottitis or tracheitis, localized abscess, and angioedema. Inflammation of the larynx and trachea with subglottic narrowing causes localized obstruction, which is enhanced by inspiration related to the extrathoracic location of the obstruction and the compliance of the airway walls in children. In addition, inflammatory changes occur throughout the lower respiratory tract.
Symptoms usually abate in three to four days and can be managed at home.
Correction of hypoxemia is essential for hospitalized patients. Aerosolized racemic epinephrine provides transient benefit for those with persistent stridor. It is most closely associated with RSV infection, which is detected in about 75 percent of infants hospitalized with bronchiolitis, and less with parainfluenza viruses, influenza viruses, rhinoviruses, and adenoviruses. The peak incidence is between two and six months of age, and over 80 percent of cases occur in the first year of life. After several days of coryza and fever, patients experience acute respiratory distress, wheezing, cough, and, often, inspiratory rales.