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Clinicians commonly misidentify respiratory sounds in children

AAP 2011 National Conference

BOSTON — Wheeze, stridor and cough are among the most common sounds made by children with respiratory conditions, but they are often misidentified, especially in the emergency department, according to a presenter here at the American Academy of Pediatrics 2011 National Conference and Exhibition.

Miles Weinberger, MD, professor of Pediatrics and director of the Pediatric Allergy and Pulmonary Division at the University of Iowa Children’s Hospital in Iowa City, Iowa, provided a breakdown of these common sounds and their causes. He stressed the importance of listening and observing the child carefully.

Weinberger said pediatricians should evaluate whether sounds are inspiratory or expiratory, continuous or interrupted, or high-pitched or low-pitched. They should also note the volume, location, duration and frequency of the sound.

Wheeze

Wheezing is characterized by continuous musical sounds that are typically expiratory. Wheezing can be caused by bronchiolitis, asthma, cystic fibrosis, a foreign body or bronchomalacia.

“Bronchiolitis is an important cause of wheezing among infants,” Weinberger said. “The symptoms of asthma and bronchiolitis are very similar but the difference is that asthma is recurrent and not just a single episode as in bronchiolitis.”

There are different characteristics of wheezing, according to Weinberger. Wheezing caused by a foreign body has a monophonic sound, in contrast to the polyphonic sound of wheezing caused by asthma and bronchiolitis.

“Especially with asthma, it sounds like an orchestra tuning up, with multiple sounds,” he said.

Parents will often tell the pediatrician that their child has been wheezing. However, what parents call wheezing is not always true wheezing. In fact, a study from 2000 reported that there is less than 50% agreement between parents and clinicians on what is truly wheezing. “Wheeze” is the most commonly used term for describing respiratory sounds.

Stridor

In contrast to the continuous steady sound of wheezing, stridor is a musical sound with varying pitch. Stridor is common and appears in about 60% of infants.

Common causes of stridor include croup, epiglottitis and laryngomalacia. Chiari malformation, vocal cord paralysis and laryngeal foreign body are less common causes. Vocal cord dysfunction syndrome can also cause stridor, but is very rare.

“Laryngomalacia is certainly the most common cause of inspiratory stridor,” Weinberger said, adding that it represents a delay in maturation of supporting laryngeal structures.

The condition typically resolves by aged 2 years and is generally benign. However, “rare cases can result in pulmonary hypertension,” he said. “It is something to watch for in children with persistent laryngomalacia because it does delay their growth and weight gain.”

Croup is the transient inflammation of the laryngeal area causing upper airway obstruction characterized by inspiratory stridor that is generally caused by a virus. Parainfluenza type 1 is the most common cause of croup, followed by respiratory syncytial virus and Mycoplasma pneumoniae.

However, Weinberger stressed to the audience that a “croupy cough” is not croup: “Croup involves the laryngeal area and is stridor,” he said.

Epiglottitis, which is caused by a bacterial infection, is currently a much less common cause of stridor because of widespread use of Haemophilus influenzae type b vaccines, according to Weinberger. Streptococcus pyogenes is also a common cause, and this infection can be life-threatening.

Weinberger said that there has been some confusion in the past between croup and epiglottitis. As a result, children were being sent for lateral neck X-rays for croup.

“Epiglottitis looks and sounds nothing like croup. There is no cough,” Weinberger said.

Vocal cord dysfunction syndrome (VCDS) is often misdiagnosed as asthma, and may present in addition to asthma. This condition can be spontaneous or exercise-induced.

Cough

Cough, defined as forceful exhalation after quickly raising thoracoabdominal pressure, is caused by pertussis, protracted bacterial bronchitis, acute viral bronchitis, asthma, M. or Chlamydia pneumoniae, aspiration, cystic fibrosis, primary ciliary dyskinesia and possibly post-nasal drip and gastroesophageal reflux disease.

Thanks to vaccines, classic pertussis, which was once known as the “100-day cough,” is relatively uncommon.

“However, this disease is endemic in our population because pertussis immunization has the lowest degree of complete effectiveness of all the vaccines that children receive,” he said. “But we do see pertussis, generally modified to an extent in immunized populations. It is important to identify those with pertussis — not because we can cure them, but because we can make them non-infectious [by treating with azithromycin] and decrease the risk of the diseases being transmitted to infants who are at substantial risk.”

Habit cough syndrome is characterized by a dry, barking cough that can last for months and is sometimes misdiagnosed as asthma or tracheomalacia. However, Weinberger said that this diagnosis can be made easily if the child does not cough at night.

“If the child does not cough at night, there is no organic cause for it and there is no reason to do other diagnostic tests,” he said.

Disclosure: Dr. Weinberger reports no relevant financial disclosures.

This presentation describes well the differential of these common respiratory signs among children. However, even for those with the ear of an orchestra conductor, delineating these respiratory signs is often challenging, especially among infants who have rapid respiratory rates, an average 50 to 40 per minute during the first 6 months of life, and who are often uncooperative. During the coming winter months the number of infants with respiratory infections being seen at emergency departments, clinics and private offices will markedly increase, and wheezing will be the most frequent lower respiratory tract sign. The great majority will have viral bronchiolitis, the number one cause of hospitalization in the US among children in the first year of life. Respiratory syncytial virus alone is estimated to cause each year approximately 10 to 20 office visits to pediatric practices among every 100 children in the first year of life. Nevertheless, detection of this common illness is often confounded by what is considered the hallmark of bronchiolitis, the variability of the characteristic auscultatory findings. Indeed, the wheezing and crackles may be intermittently absent. This emphasizes the importance of repetitive examinations and a good history in detecting and differentiating bronchiolitis from other less common causes of airway obstruction.

Caroline Breese Hall, MD
Professor of Pediatrics and Medicine
University of Rochester School of Medicine and Dentistry

Disclosure: Dr. Hall reports no financial disclosures.

For more information:

• Weinberger M. #F1123. Wheeze, stridor, cough and other respiratory noises. Presented at: AAP 2011 National Conference and Exhibition. Oct 15-18, 2011. Boston.