Crup

Acute Bronchiolitis a nd Croup
Mark L. Everard, MB, ChB, FRCP, DM
KEYWORDS  Acute bronchiolitis  Croup  Wheeze  Wheezy bronchitis

Respiratory viruses are responsible for an extremely high proportion of all disease in young children presenting to medical services. Preschool children infected by one of these pathogens usually exhibit clinical illness with one or more upper airwaysmanifestations such as coryza, pharyngitis, or otitis media. Extension of infection into the lower airways below the larynx most commonly causes ‘‘bronchitis,’’ adding cough to the symptoms associated with the previously mentioned conditions. If the virus induces airways obstruction (most commonly through the induction of increased airways secretions and mucosal edema and/or bronchospasm), thisobstruction may be manifest by increased work of breathing resulting in tachypnea and subcostal recession, gas trapping as manifested by hyperinflation, and noisy breathing caused by turbulent airflow. The clinical phenotype of disease induced by a viral lower respiratory tract infection is determined by a number of factors, including the site of maximal inflammation, which in turn depends in part on thevirus, the age of the infant or young child, and the existence of comorbidities such as atopic asthma. Although certain viruses classically are associated with certain disease phenotypes, such as parainfluenza with croup, respiratory syncytial virus (RSV) with acute bronchiolitis, and rhinovirus with exacerbation of asthma, any of the viruses can induce any of the clinical phenotypes.1–5 The acutebronchiolitis associated with rhinovirus is clinically indistinguishable from that caused by RSV; RSV also is an important cause of croup and is responsible for a significant proportion of exacerbations of asthma in young children. The number of viruses known to target the respiratory tract continues to grow; viruses such as human metpneumovirus and human bocavirus have been added to the list ofproven and likely respiratory pathogens.5 As Fig. 1 indicates for RSV (see Fig. 1A) and rhinovirus (see Fig. 1B), any of the conditions can be caused by any of the viruses, but the relative likelihood if a particular virus causing a particular condition varies with the virus. One of the great challenges for those dealing with lower respiratory tract disease in children is that the lungs have a verylimited repertoire of responses to acute or chronic insults. Increased airways secretions and cough are common to many conditions, such as acute or persistent bacterial infections, acute viral infections, untreated

Department of Respiratory Medicine, Sheffield Children’s Hospital, Western Bank, Sheffield S10 2TH, UK E-mail address: m.l.everard@sheffield.ac.uk Pediatr Clin N Am 56 (2009) 119–133doi:10.1016/j.pcl.2008.10.007 pediatric.theclinics.com 0031-3955/08/$ – see front matter ª 2009 Elsevier Inc. All rights reserved.

120

Everard

Fig. 1. Phenotypes of respiratory illness caused by respiratory syncytial virus and rhinovirus.

asthma, and recurrent aspiration. In some individuals bronchoconstriction also can contribute to airways obstruction. Disease within the lowerairways frequently leads to the generation of adventitial sounds. Secretions within the large airways can induce audible rattles and coarse airways noises6,7 but also may contribute to the wheeze in patients experiencing an exacerbation of asthma or wheezy bronchitis. The lack of precision in using the term ‘‘wheeze’’ adds to the difficulties in this area. It is clear that parents and doctors use theterm ‘‘wheeze’’ for a variety of respiratory, and indeed nonrespiratory, noises.7–9 Because wheeze is a key symptom driving both diagnostic and therapeutic decisions, this imprecision is a major problem. Obstruction of distal airways with secretions may lead to the generation of inspiratory crackles (crepitations) heard on auscultation as units of alveoli pop open. The lack of a simple test to...