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Infectious Disease and Microbiology - Laryngitis/Laryngotracheobronchitis (Croup)
Laryngitis refers to inflammation of the laryngeal mucosa, while laryngotracheobronchitis, commonly known as croup, involves inflammation of the subglottic airway, trachea, and bronchi. These conditions are most often caused by viral infections and typically present as part of an upper respiratory tract illness. Croup is particularly common in young children, especially between 3 months and 3 years of age, and tends to occur more frequently in boys.
The epidemiology reflects seasonal viral patterns. Laryngitis commonly occurs during winter in association with respiratory infections. Croup is most frequently caused by Parainfluenza virus type 1, especially in the fall, while Influenza virus and Respiratory syncytial virus contribute during winter and early spring. Other pathogens such as adenovirus, rhinovirus, enterovirus, and Mycoplasma pneumoniae may also be involved.
Risk factors for laryngitis include smoking, alcohol use, immunosuppression, and close contact with infected individuals. In croup, young age and possible variations in immune response play a major role. Prevention is mainly through avoidance of infected individuals and proper hand hygiene.
The underlying pathophysiology involves viral infection leading to inflammation, edema, and narrowing of the airway. In croup, subglottic swelling leads to airway obstruction, which is more pronounced in children due to their smaller airway diameter. This results in the characteristic stridor and respiratory distress.
Clinically, laryngitis presents with hoarseness, reduced voice pitch, and sometimes aphonia. In severe cases, airway obstruction may lead to stridor. Croup typically begins with fever followed by hoarseness and a distinctive “barking” cough. Inspiratory stridor, tachypnea, and chest wall retractions are common findings. In more severe cases, both inspiratory and expiratory stridor, wheezing, and signs of respiratory distress such as tachycardia and fatigue may develop.
Diagnosis is primarily clinical. Laboratory findings are usually normal, although hypoxemia may occur in severe cases. Imaging is not routinely required but may support the diagnosis. A classic anterior–posterior neck x-ray in croup shows subglottic narrowing known as the “steeple sign.”
Management depends on severity. Mild laryngitis is usually treated with supportive care such as humidified air, and medications are not required unless bacterial infection is suspected. In croup, corticosteroids such as dexamethasone are the mainstay of treatment and significantly improve symptoms. Nebulized epinephrine may be used in moderate to severe cases for temporary relief of airway obstruction, but patients require observation due to possible rebound symptoms. Supplemental oxygen is used in cases of hypoxemia, and severe cases may require intubation and mechanical ventilation.
The overall prognosis is excellent, with most cases resolving within a few days, although cough may persist longer. Complications are uncommon but may include airway obstruction and respiratory failure in severe croup. Rare complications include pneumothorax, pulmonary edema, and secondary infections. Long-term effects such as airway hyperreactivity or subglottic stenosis may occur in severe or recurrent cases.
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