Discussion:
With increasing use of bronchoscopic examination in paediatric patient
and developing devices of suitable size for small children, airway
malacia disorders are becoming well recognized. However, the true
incidence of airway malacia is not well known. According to the English
literature, two studies that enrolled the highest numbers of patients
revealed that the incidence of airway malacia among patients underwent
bronchoscopy is 16.6% and 34%. In the latter, authors included
patients with laryngomalacia in their study 5,6. We
found the incidence rate similar to the first study (16.6%). There are
several reasons why the true incidence is not well known. There is no
standardized diagnostic criterion of airway malacia. In 2019, ERS Task
force report is suggested definition of airway malacia as greater the
50% expiratory reduction in the cross-sectional luminal area during
quiet respiration; but some centres has used the 25% or 33% expiratory
reduction for diagnosis 4. Furthermore, in some
paediatric pulmonology centres, suitable bronchoscopy device for small
infants or new-borns may not be available and lack of device may cause
the diagnosis to be delayed or missed. Deficient knowledge or lack of
suspicion of general practitioners, even of some paediatricians, about
airway malacia may also cause the patients to be undiagnosed. A
significant amount of patients with lower airway malacia might be
misdiagnosed as asthma.
The type and onset of symptoms depend on localization and severity of
the malacic segment. We did not evaluate the onset time in our study,
but we found that the most common clinical symptom was recurrent and/or
prolonged respiratory infection. The high percentages of respiratory
infections in our study may be related to the higher number of cases
with BM. Airway malacia is a frequent bronchoscopic finding in children
with recurrent respiratory infection and protracted bacterial
bronchitis, although it is not known exactly whether malacia is cause or
result of respiratory infection 7,8. Only five of the
BM cases with a history of recurrent and/or prolonged respiratory
infection had positive BAL culture, and that represents 10.4% of all BM
cases. Overall, 22.6% of BAL samples were culture positive. The cause
of such a low rate may be related to take BAL samples while some of the
patients were under antibiotic treatment.
The most common physical examination finding was stridor in our study.
Stridor is mainly related to narrowing of extra thoracic airway.
Although the most common airway malacia type was BM in our study, the
high frequency of stridor might be related to accompanying
laryngomalacia.
Airway malacias are classified as primary (congenital) and secondary
(acquaried) malacia according to time of abnormal formation on the
airways 4. Although no etiological factor could be
found for eight patients to develope malacia in our study, it is
difficult to classify them as primary airway malacia. Since, detecting
persistence of a malacia during bronchoscopy despite proper treatment is
necessary to name a malacia as primary. However, we did not perform any
bronchoscopy after treatment to see whether malacia was persisting or
not. Therefore, we did not make such a classification in our study.
In our study, the most common diseases associated with airway malacias
were GERD and swallowing dysfunction. The relationship between GERD and
airway malacia has been shown in several studies. The high prevalence of
gastroesophageal reflux among infants with airways malacia can be
related to the negative intrapleural pressure induced by airflow
obstruction during respiration and this pressure leads to a malfunction
of the lower gastroesophageal sphincter and causes reflux. It is also
shown that after antireflux therapy; respiratory symptoms were
decreased. The improvement may be related to preventing chronic injury
to the lung or it may have occurred spontaneously.9,10. More detailed research is required to show this
difference. Swallowing dysfunction is also common among airway malacias,
or maybe we should say airway malacias are common in patients who have
swallowing dysfunction. Although the reason of this association is not
well known, it might be related to chronic inflammation of airways due
to chronic aspiration.
There is no universally agreed gold standard diagnostic test for airway
malacias; but flexible bronchoscopy is the most commonly used diagnostic
modality. However, bronchoscopy is an invasive and subjective procedure.
Furthermore, it increases end expiratory airway pressure and it can be
difficult to detect some mild malacias during bronchoscopy. Chest CT is
a valuable test to diagnose respiratory diseases. It could assist to
find secondary factors causing malacia after diagnosis or show
supporting findings such as stenosis, increased/decreased inflation. In
recent years, contrast enhanced multi-detector computed tomography
(MDCT) has become an alternative modality to aid in the diagnosis of
airway malacia in children by obtaining information about the calibre
change of the large airways at both end-inspiration and end-expiration
(paired end-inspiratory and end-expiratory) 11.
However, it is very difficult to apply this dynamic technique in
paediatric patients, and it is available in limited numbers of tertiary
centres. Although we diagnosed airway malacia by performing flexible
bronchoscopy, 56 patients were also performed thoracic non-dynamic CT
and 10 of them revealed narrowing of the airway on malacic region.
Previously airway malacia, especially congenital form, has been thought
to be self-limited and improved by the second year of life without
intervention 12. Although the majority of the patients
were under two years old, none of them were followed without any
intervention in our study.
Treatment of malacia depends on the aetiology and severity of the airway
collapse. Treatment options include medical and surgical therapy, chest
physiotherapy and ventilator support. However, there are no
randomised-controlled studies for treatment in airway malacia.
One of the leading medical therapies in malacia is inhaled ipratropium
bromide. Although its mechanism is not fully known, it is thought to
have an effect on airway muscular tone. In recent animal and human
studies showed airway dynamics of trachea are affected by tracheal
smooth muscle contraction by cholinergic stimulation13,14. Although inhaled ipratropium bromide is an
anticholinergic agent, it stimulates smooth muscle contraction by
blocking presynaptic muscarinic receptors (M2), which provide feedback
inhibition for acetylcholine release in the neuromuscular junction, in
low doses 15. Relying on this effect, inhaled
ipratropium bromide therapy was started in patients with malacia in our
clinic. However, reliable data could not be obtained from our hospital
records about the duration of inhaled ipratropium bromide therapy that
improved the symptoms of the patients. In addition, none of the patients
underwent control bronchoscopy to assess the improvement in the malacic
region. There is only one study in the literature about the effect of 6
months of atropine treatment on clinical improvement; but no data were
available when the treatment should be terminated 16.
Tracheostomy with or without long-term invasive MV was the mainstay of
treatment for severe TM in the past. However, because of its
life-threatening complications and remarkable advance in non-invasive
therapies, tracheostomy without invasive MV is currently used as a last
resort. In our study, tracheostomy was performed in 15% of the patients
due to need for invasive MV however, invasive MV indication was not only
airway malacia but also respiratory failure related to associated
conditions in all of them. Non-invasive MV is another treatment method
of malacia. Positive pressure creates a pneumatic stent and prevents the
collapse of the airway during respiration 4. Although,
only one patient, who had severe bronchomalacia on bilateral main
bronchus, was treated with non-invasive MV in our study. we believe
that, it will be the first treatment of choice for severe malacia in the
future.