Croup: Pathogenesis and clinical findings
Viral pathogen (parainfluenza, respiratory syncytial virus, influenza virus,
Authors: Christy Chong, Nick Baldwin Reviewers: Tara Shannon, Jody Platt, Elizabeth de Klerk, Yan Yu*, Naminder Sandhu*, Danielle Nelson* *MD at time of publication
measles morbillivirus, or adenovirus) colonizes the nasopharyngeal mucosa
Virus migrates along epithelium and invades the upper airways in the larynx and trachea
Croup (laryngotracheobronchitis)
Cytokines disrupt hypothalamic thermoregulation
Fever Refer to
Fever: Pathogenesis slide
Laryngeal swelling compresses vocal cords
Hoarseness of voice
Infection of the larynx, trachea, and bronchi – typically in children 6 years or younger in the Fall and Winter
Host immune response to virus ↑ inflammatory cytokine release into circulation à Immune cells migrate to sites of infection and produce free radicals to fight off virus
Damage to healthy cells within the upper airways
↑ Permeability of blood vessels within the upper airways
Protein and fluid leak into nasopharyngeal, laryngopharyngeal, and/or tracheal interstitiums
↓ Ciliary cells (responsible for clearing mucous and dirt from the respiratory tract)
↓ Mucous movement across airway
Nasal mucous discharge
Nasal edema and swelling
Nasal congestion
↑ Tracheal mucous Trachea is narrowed and clogged
↓ Diameter of trachea
↓ Air pressure inside the tracheaàtracheal wall collapses (Bernoulli’s principle)
↑ Nasal mucous
Immature/less rigid tracheal walls in young children susceptible to further structural narrowing
Breathing across a narrowed trachea à turbulent airstreams ↑ Work of breathing to adequately ventilate lungs with O2
Inspiratory stridor Expiratory Children rely on compensatory respiratory mechanisms as they fatigue overtime
(harsh, high- “barking” cough pitched sound)
Respiratory distress
Nasal flaring Chest-wall in-drawing Tachypnea Accessory respiratory muscle use
Legend:
Pathophysiology
Mechanism
Sign/Symptom/Lab Finding
Complications
First published May 28, 2013, Updated September 3, 2022 on www.thecalgaryguide.com