VIRAL CROUP
Def.: heterogeneous group of mainly acute and infectious upper airway obstruction processes that are characterized by a barking like or brassy cough and may be associated with hoarseness, inspiratory stridor, and respiratory distress.
It is acute laryngotracheitis, Laryngotracheobronchitis!
Incidence:
· The most common form of acute upper respiratory obstruction.
· Affect about 15% of children.
· It is most common between 6 m΄ and 6 years of age, with a peak prevalence in the 2nd year of life, rare over the age of 10 years.
· Boys > girls.
· Season; a peak in autumn and winter is associated with parainfluenza virus but can occur throughout the year.
· Croup is uncommon < 6 months of life.
· Rarely lasts more than 10 to 14 days.
· Approximately 15% of patients have a strong FHx of croup.
ETIOLOGY:
· Parainfluenza viruses type 1 , 2 and 3 (account for ≈75% of cases(
· Other viruses including RSV, adenovirus, influenza, and measles: Influenza has been associated with more severe cases.
Pathogenesis:
· After inhalation of the virus, the cells of the local respiratory epithelium become infected.
· There is marked edema of the lamina propria, submucosa, and adventitia accompanied by cellular infiltration with histiocytes, lymphocytes, plasma cells, and PNLs.
· The infant’s glottis and subglottic region are normally narrow, and a small ↓ in diameter → large ↑ in airway resistance & ↓ in airflow.
