Croup is acute inflammation of the upper and lower respiratory tracts most commonly caused by parainfluenza virus type 1 infection. It is characterized by a barking cough and inspiratory stridor. Diagnosis is usually obvious clinically but can be made by anteroposterior neck x-ray. Treatment is antipyretics, hydration, nebulized racemic epinephrine, and corticosteroids. Prognosis is excellent.

Croup affects mainly children aged 6 mo to 3 yr.

Etiology

The parainfluenza viruses, especially type 1, are the most common pathogens. Less common causes are respiratory syncytial virus (RSV) and influenza A and B viruses, followed by adenovirus, enterovirus, rhinovirus, measles virus, and Mycoplasma pneumoniae. Croup caused by influenza may be particularly severe and may occur in a broader age range of children.

Seasonal outbreaks are common. Cases caused by parainfluenza viruses tend to occur in the fall; those caused by RSV and influenza viruses tend to occur in the winter and spring. Spread is usually through the air or by contact with infected secretions.

Pathophysiology

The infection causes inflammation of the larynx, trachea, bronchi, bronchioles, and lung parenchyma. Obstruction caused by swelling and inflammatory exudates develops and becomes pronounced in the subglottic region. Obstruction increases the work of breathing; rarely, tiring results in hypercapnia. Atelectasis may occur concurrently if the bronchioles become obstructed.

Symptoms and Signs

Croup is usually preceded by URI symptoms. A barking, often spasmodic, cough and hoarseness then occur, commonly at night; inspiratory stridor may be present as well. The child may awaken at night with respiratory distress, tachypnea, and retractions. In severe cases, cyanosis with increasingly shallow respirations may develop as the child tires.

X-Rays of a Child With Croup

X-Rays of a Child With Croup

The obvious respiratory distress and harsh inspiratory stridor are the most dramatic physical findings. Auscultation reveals prolonged inspiration and stridor. Rales also may be present, indicating lower airway involvement. Breath sounds may be diminished with atelectasis. Fever is present in about half of children. The child's condition may seem to have improved in the morning but worsens again at night.

Recurrent episodes are often called spasmodic croup. Allergy or airway reactivity may play a role in spasmodic croup, but the clinical manifestations cannot be differentiated from those of viral croup. Also, spasmodic croup usually is initiated by a viral infection.

Diagnosis

• Clinical presentation (eg, barking cough, inspiratory stridor)
• Anteroposterior (AP) and lateral neck x-rays as needed

Diagnosis is usually obvious by the barking nature of the cough. Similar inspiratory stridor can result from epiglottitis, bacterial tracheitis, foreign body, diphtheria, and retropharyngeal abscess. Epiglottitis (see Oral and Pharyngeal Disorders: Epiglottitis), retropharyngeal abscess (see Oral and Pharyngeal Disorders: Retropharyngeal Abscess), and bacterial tracheitis (see Respiratory Disorders in Neonates, Infants, and Young Children: Bacterial Tracheitis) have a more rapid onset and cause a more toxic appearance, odynophagia, and fewer upper respiratory tract symptoms. A foreign body may cause respiratory distress and a typical croupy cough, but fever and a preceding URI are absent. Diphtheria is excluded by a history of adequate immunization and is confirmed by identification of the organism in viral cultures of scrapings from typical grayish diphtheritic membrane.

If the diagnosis is unclear, patients should have AP and lateral x-rays of the neck and chest; subepiglottic narrowing (steeple sign) seen on AP neck x-ray supports the diagnosis. Seriously ill patients, in whom epiglottitis is a concern, should be examined in the operating room by appropriate specialists able to establish an airway (see Oral and Pharyngeal Disorders: Treatment). Patients should have pulse oximetry, and those with respiratory distress should have ABG measurement.

Treatment

• For outpatients, cool humidified air and possibly a single dose of oral corticosteroids
• For inpatients, humidified O₂, racemic epinephrine, and oral corticosteroids

The illness usually lasts 3 to 4 days and resolves spontaneously. A mildly ill child may be cared for at home with hydration and antipyretics. Keeping the child comfortable is important, because fatigue and crying can aggravate the condition. Humidification devices (eg, cold-steam vaporizers or humidifiers) may ameliorate upper airway drying and are frequently used at home by families but have not been shown to alter the course of the illness. The vast majority of children with croup recover completely.

Increasing or persistent respiratory distress, tachycardia, fatigue, cyanosis or hypoxemia, or dehydration indicates need for hospitalization. Pulse oximetry is helpful for assessing and monitoring severe cases. If O₂ saturation falls below 92%, humidified O₂ should be given, and ABGs should be measured to assess CO₂ retention. A 30 to 40% inspired O₂ concentration is usually adequate. CO₂ retention (Paco₂ > 45 mm Hg) generally indicates fatigue and the need for endotracheal intubation, as does inability to maintain oxygenation.

Nebulized racemic epinephrine 5 to 10 mg in 3 mL of saline q 2 h offers symptom relief and relieves fatigue. However, the effects are transient; the course of the illness, the underlying viral infection, and the Pao₂ are not altered by its use. Tachycardia and other adverse effects may occur.

High-dose dexamethasone 0.6 mg/kg IM or po once (maximum dose 10 mg) may benefit children early in the first 24 h of the disease. It can help prevent hospitalization or help the child who is hospitalized with moderate to severe croup. The viruses that most commonly cause croup do not usually predispose to secondary bacterial infection, and antibiotics are rarely indicated.

Last full review/revision March 2009 by Anand D. Kantak, MD; John T. McBride, MD