Croup is a viral disease of the respiratory tract, mainly pediatric. Their alternative names, acute laryngotracheitis, and acute laryngotracheobronchitis, indicate that croup generally affects the larynx and trachea, although this disease can also extend to the bronchi.
Croup is the most common etiology for hoarseness, cough, and the onset of acute stridor in children with fever. The vast majority of children with croup recover without consequences or consequences however, it can endanger the lives of tiny babies.
Croup manifests as hoarseness, pricking cough, inspiratory stridor, and a variable degree of respiratory distress.
However, morbidity is secondary to narrowing the larynx and trachea below the glottis level, causing the characteristic auditory inspiratory stridor.
Stridor is a common symptom in patients with croup. The acute onset of this abnormal sound in a child alarms parents and caregivers enough to request an urgent care visit or emergency department.
It is an audible and sharp musical sound inspired by the turbulent airflow through a partially obstructed upper airway.
This partial airway obstruction may be present at the supraglottis, glottis, subglottis, and trachea levels.
Depending on the time within the respiratory cycle, the stridor can be heard with inspiration, expiration, or both (inspiratory and expiratory). Inspiratory stridor suggests a laryngeal obstruction, while expiratory stridor suggests a tracheobronchial block.
Biphasic stridor indicates a subglottic or glottic anomaly. Acute onset of marked inspiratory stridor is the hallmark of croup. However, there may be less audible expiratory stridor at the same time.
Tiny babies who have stridor require a thorough evaluation to determine the etiology and, most importantly, to exclude life-threatening causes.
Although croup is usually a mild and self-limiting disease, obstruction of the upper airway can cause respiratory distress and present a risk of death.
The viruses that cause acute infectious croup are transmitted through the direct inhalation of cough and sneezing or by contamination of the hands by contact with fomites with the mucosa of the eyes, nose, and mouth.
The most common viral etiologies are parainfluenza viruses. The type of parainfluenza viruses (1, 2, and 3) that cause outbreaks of croup vary each year.
The main ports of viral entry are the nose and nasopharynx. The infection spreads and eventually involves the larynx and trachea.
The lower respiratory tract may also be affected, as in acute laryngotracheobronchitis.
Some doctors feel that with a lower involvement of the respiratory tract, a more excellent diagnostic evaluation is warranted to address the concern of a secondary bacterial infection.
Inflammation and edema of the subglottic larynx and trachea, especially near the cricoid cartilage, are clinically significant.
The parainfluenza virus activates chloride secretion and inhibits the absorption of sodium through the tracheal epithelium, which contributes to the edema of the respiratory tract.
The affected anatomical area is the narrowest part of the pediatric airway; consequently, the swelling can significantly reduce the diameter, limiting the airflow.
This narrowing results in a cough with a particular sound, turbulent airflow, stridor, and chest wall retractions.
Endothelial damage and loss of ciliary function also occur. Decreased mobility of the vocal cords due to edema leads to associated hoarseness.
Fibrinous exudates and pseudomembranes may develop in severe cases, causing even more significant airway obstruction. Hypoxaemia can occur due to progressive narrowing.
Spasmodic croup is a noninfectious variant of the disorder, with a clinical presentation similar to the acute disease but usually without fever.
This type of croup always occurs at night. Therefore it has also been called “recurrent croup.” Subglottic edema occurs without the typical inflammation in acute viral disease in spasmodic croup.
Although viral diseases can trigger this variant, the reaction may be of allergic etiology rather than a direct result of an infectious process.
The parainfluenza viruses (types 1, 2, and 3) are responsible for about 80% of cases of croup, with parainfluenza types 1 and 2, which represent almost 66% of cases.
The type 3 parainfluenza virus causes bronchiolitis and pneumonia in infants and young children. Parainfluenza virus type 4, with subtypes 4A and 4B, is not well understood and is associated with milder clinical disease.
The different types of parainfluenza play a more prominent role in the infectious process about the patient’s age.
Infection with type 3 occurs most frequently in babies and is the etiology of lower respiratory tract disease; 50% of babies have acquired this infection at one year.
Respiratory infections in children 1 to 5 years of age are more often due to type 1 and less so to type 2.
Infection with influenza A is associated with the severe respiratory disease since it has been detected in children with significant respiratory compromise.
The bacterial pathogen, Mycoplasma pneumonia has also been identified in some cases of croup. Before 1970, diphtheria, also known as membranous croup, was a common cause of croup-like symptoms.
Croup is usually self-limiting and has an excellent long-term global prognosis.