Croup is a group of respiratory diseases that often affects infants and children under age 6. It is characterized by a barking cough; a whistling, obstructive sound (stridor) as the child breathes in; and hoarseness due to obstruction in the region of the larynx. It may be mild, moderate or severe, and severe cases, with breathing difficulty, can be fatal if not treated in a hospital. Another type of croup is known as spasmodic croup. People with spasmodic croup first catch a cold, rarely with fever, and then the croupy cough begins. In some cases spasmodic croup may begin suddenly without any preceding cold symptoms. Unlike viral croup, spasmodic croup usually recurs, can occur in older children, and rarely even in adults. Spasmodic croup is thought to be related to allergies.
Croup affects 5% of children in the second year of life; the peak incidence is 3 months to 3 years. The group of respiratory diseases consists of spasmodic croup, acute laryngotracheitis, laryngotracheobronchitis (LTB), laryngotracheobronchopneumonitis (LTBP), and laryngeal diphtheria. LTB and LTBP, which usually involve a bacterial infection, are usually severe.
The first step in diagnosis is to exclude other acute obstructive illnesses in the region of the larynx, such as epiglottitis, a foreign body, or angioneurotic edema of the epiglottis. Misdiagnosing an obstructive airway disease can be fatal.
Signs and symptoms
Croup is characterized by a harsh "barking" cough and sneeze, inspiratory stridor (a high-pitched sound heard on inhalation), nausea/vomiting, and fever. Hoarseness is usually present. More severe cases will have respiratory distress.
The "barking" cough (often described as seal-like) of croup is diagnostic. Stridor will be provoked or worsened by agitation or crying. If stridor is also heard when the child is calm, critical narrowing of the airway may be imminent.
In diagnosing croup, it is important for the physician to consider and exclude other causes of shortness of breath and stridor, such as foreign body aspiration and epiglottitis.
On a frontal X-ray of the cervical vertebrae, the steeple sign suggests the diagnosis of croup.
Croup is most often caused by parainfluenza virus, primarily types 1 and 2 (some definitions limit the term "croup" to this pathogen). However, other viral and possibly bacterial infections can also cause it. Approximately 75% of cases are caused by parainfluenza virus. Influenza A and B, Measles, adenovirus and respiratory syncytial virus (RSV) are other viruses that sometimes cause croup. It is most common in the fall and winter but can occur year-round, with a slight predilection for males.
The respiratory distress is caused by the inflammatory response to the infection, rather than by the infection itself. It usually occurs in young children as their airways are smaller and differently shaped than adults', making them more susceptible. There is some element of genetic predisposition as children in some families are more susceptible than others.
An entity known as spasmodic croup also occurs, distinct from the infectious variety, due to laryngeal spasms.
The treatment of croup depends on the severity of symptoms.
The Alberta Clinical Practice Guideline Working Group has developed guidelines for diagnosing and treating croup, including a scoring system for classifying severity. The severe form (which affected less than 1% of children seen in the emergency department) involves breathing difficulties, indicated by stridor, chest retractions, agitation and distress. Lethargy or decreased level of consciousness is a sign of impending respiratory failure, and requires emergency medical treatment. LTB and LTBP are usually severe, and require treatment in the intensive care unit, with an endotracheal (ET) tube to assist breathing and antibiotics.
The routinely recommended treatment is with corticosteroids, although corticosteroids suppress the immune system and can predispose the child to infection. There is a debate over how many doses to give, but Cherry in the New England Journal of Medicine recommends one dose, and has observed that children with viral, bacterial and fungal complications have had multiple doses. Epinephrine produces a significant reduction in the croup severity score but the benefit only lasts for 2 hours. Children who have moderate or severe croup with blood oxygen saturation under 92% should receive oxygen.
Since laryngotracheitis is a viral disease (most commonly parainfluenza virus 1) antibiotics have no value.
Croup can be prevented by immunization for influenza and diphtheria. At one time, croup referred to a diphtherial disease, but with vaccination diphtheria is rare.
One of the traditional ways to treat croup is to inhale hot steam. However, studies have found that this is not effective. This was the sole treatment for croup throughout the nineteenth and most of the twentieth century. Hospitals today use a "blowby" apparatus for this purpose. Simpler remedies include taking the child outside in moist night air, or alternatively exposing the child to steam from a hot bath or a humidifier. There is little or no evidence to support their efficacy.
Mild croup with no stridor, or stridor only on agitation, and just a cough may simply be observed, or a dose of inhaled, oral, or injected steroids may be given. When steroids are given, dexamethasone is often used, due to its prolonged physiologic effects.
Moderate to severe croup may require nebulized adrenaline in addition to steroids. Oxygen may be needed if hypoxia develops. Children with moderate or severe croup are typically hospitalized for observation, usually for less than a day. Intubation is rarely needed (less than 1% of hospitalized patients).
Viral croup is a self-limited disease, but can very rarely result in death from complete airway obstruction. Symptoms may last up to 7 days, but typically peak around the second day of illness. Rarely, croup can be complicated by, (or confused with) an acute bacterial tracheitis, which is more dangerous.