Discussion
Children afflicted with SMPP have severe clinical symptoms and more
complications than those with MPP, including necrotizing pneumonia,
atelectasis, bronchiectasis, OB, and permanent airway structural damage.
As a result, lung function declines and repeated infections can impact
quality of life for these patients. According to previous studies, main
clinical manifestations of pediatric SMPP include continuous high fever
and the presence of large areas of
lung consolidation detected via pulmonary imaging. These findings
reflect an overactive immune response that often requires hormone
therapy for suppression of harmful inflammatory
processes.7-9
The clinicalClinical manifestations of MPP in China differ from those
reported in other countries, with symptoms more serious in China,
especially in northern areas.4 In recent years, the
widespread application of pediatric bronchoscopy for SMPP diagnosis and
treatment has led to great progress in treating this disorder in China.
Although some practitioners doubt the value of bronchoscopic findings
for MPP prognosis, the value of bronchoscopy has been demonstrated for
pediatric SMPP prognosis in China. In this study, congestion and
swelling of airway mucosa were obvious in acute-stage cases examined via
bronchoscopy, with some of these findings accompanied by follicular
hyperplasia, a relatively specific MPP-associated manifestation.
Meanwhile, during bronchoscopy bronchoalveolar lavage fluid is readily
collected for use in MPP pathogen detection as a direct and effective
method for achieving differential MPP diagnosis and treatment.
Importantly, acute-stage SMMP mucous plug obstructions should be cleared
bronchoscopically in a timely manner in order to maintain unobstructed
airway subbranches and subsequently control infection. In subacute-stage
SMMP, bronchoscopy can be used to monitor recovery from airway
inflammation and detect OB sequelae for use in guiding treatment and
respiratory rehabilitation planning. Therefore, bronchoscopic
examination and intervention can benefit children with SMMP, with no
significant adverse effects of bronchoscopy found in this study.
OB, a type of chronic airflow obstruction syndrome, mainly involves
small and medium bronchi and is associated with proliferation of fibrous
tissue. The main manifestations of OB are atelectasis and lobar
collapse. Under bronchoscopic examination, the distal obliterans of some
subsegmental and subsubsegmental bronchi of OB patients is accompanied
by atrophy of proximal mucosa, appearance of obvious cartilage rings,
and lumen expansion. OB often occurs secondary to severe pneumonia and
has gradually gained recognition as a common SMPP-associated
sequela,10 although few studies in China or abroad
have described OB caused by M. pneumoniae infection. With
increasing research attention paid to SMPP airway damage, OB detection
rates have significantly increased and highlight OB as an urgent
clinical problem stemming from processes underlying SMPP development.
Meanwhile, studies have shown that MP infection can result in cellular
and humoral immune dysfunction and disturbances of cytokine networks.
Moreover, an excessive inflammatory reaction causes airway mucosal
epithelial damage followed by airway subbranch injury that leads to scar
contracture and occlusion. In this study, it was observed that OB caused
by SMPP mainly involved grade III bronchi or below. The OB developmental
process could be outlined as follows: in acute-stage disease, diseased
sub-bronchi begin to erode then mucous plugs develop and blockages form.
Next, necrotic epithelium detaches and blocks the airway in the subacute
stage. Afterwards, subsegmental bronchi gradually became narrower,
leading to poor ventilation, insufficient local blood supply surrounding
lesions, then gradual formation of obliterans. The obliterans formation
process supports the conclusion that obliterans are caused by airway
injury. Meanwhile, initial obliterans lesions first appear as a thin
film that is easily reopened using biopsy forceps. Next, the occluded
part gradually thickens to form a barrier that biopsy forceps cannot
reopen in most cases. It has been suggested that it may be possible to
reopen airway branches after choosing the appropriate timing for
bronchoscopic intervention, with further study needed to optimize
interventional timing for improved treatment outcomes.
In this study, the timing of bronchoalveolar lavage was also
investigated to detect correlations with OB incidence during late-stage
SMPP. Specifically, the incidence of OB in pediatric patients who
received first bronchoalveolar lavage at 10 days post-SMPP onset was
significantly higher than that of children receiving their first
bronchoscopies within 10 days post-disease onset. It has been suggested
that for pediatric patients with persistent fever and large lung
consolidations, atelectasis, and other pulmonary pathological changes
detected via imaging within 10 days of onset, timely bronchoalveolar
lavage is recommended to avoid complications such as OB.
The main components of bronchial mucous plugs include a mixture of mucin
and cellular debris combined with a large number of infiltrating
inflammatory cells that make this mixture extremely viscous. At present,
it is widely recognized that hyperimmune inflammation is one of the main
pathogenic mechanisms underlying SMPP.3,11 MP
infection tends to lead to mucosal necrosis and mucus hypersecretion via
a mechanism that may involve direct damage and release of
infection-triggered toxic metabolites that ultimately damage bronchial
epithelial cells and cilia. Such pathological damage may further impair
mucociliary system function and weaken ciliary discharge capacity and
clearance of secretions. Afterwards, tethered secretions that form
within the local airway can trigger airway obstruction, with local
obstruction of the proximal bronchus and various sizes of mucous plugs
occurring within deep subsegmental bronchi in some serious cases. This
study demonstrated that pediatric SMMP patients who also developed OB
during late-stage disease exhibited different degrees of mucous plug
development during acute-stage SMPP that were detected via bronchoscopy.
Therefore, for patients with mixed lesions that are associated mainly
with mucous plugs, mucus necrosis, and particularly with successive
mucus plug development detected upon bronchoscopic reexamination,
localization of mucous plugs should be done as early as possible in
conjunction with administration of systemic treatment. Moreover, regular
bronchoalveolar lavage treatment would facilitate the timely removal of
mucous plugs in order to improve ventilation and secretion clearance at
lesion sites and promote inflammatory absorption.
This study demonstrated that the density of large consolidation areas
was significantly increased during acute-stage SMPP, suggesting that
subbranches can be severely blocked by mucous embolisms. Thus,
bronchoscopy should be performed as soon as possible to remove airway
secretions that in such cases consist of thick viscous mucus that is
difficult to clear away. For conducting a first bronchoscopic
examination of patients with this type of lesion, a bronchoscope with a
larger diameter (such as 4.0 mm) is recommended; because the diameter of
the suction duct is large, it can loosen and brush mucous plugs to the
depth of subsegmental bronchi and can effectively remove mucous plugs
from deeper airways with the help of a cell brush. Due to acute-stage
mucosal damage and congestion, adrenaline can be applied locally to
shrink blood vessels while plugs are slowly and gently brushed to
minimize bleeding during plug removal. During late-stage SMPP recovery
characterized by improved lung imaging findings, the 2.8-mm diameter
bronchoscope could be selected for subsequent inspection and clearance
of deep subsegmental bronchial mucous plugs.
Due to the risk of pneumothorax that may occur during bronchoscopic
examination and treatment of necrotic pediatric SMPP, the use of
bronchoscopy for such cases is still controversial at present. However,
it is worth noting that of 6 patients with late-stage necrotic pneumonia
receiving treatment in this study, all of these patients developed OB
even though they had different degrees of bronchoscopically detected
airway blockage due to mucous plugs and mucinous necrosis. Notably, no
pneumothorax occurred as a result of bronchoscopic treatment.
Nevertheless, owing to the small sample size of this study, it is
impossible to judge the advantages and disadvantages of bronchoscopy for
necrotic SMPP based solely on results of this study.
In summary, pediatric SMPP patients exhibit certain characteristics
during different disease stages that can facilitate diagnosis. However,
airway mucus and mucosal epithelial necrosis and detachment could lead
to clogging of subbranches and subsequent OB. Thus, it is recommended
that pediatric SMPP patients with mucous plugs undergo timely
bronchoscopy in addition to customary antibiotic treatment. Because this
study did not comprehensively summarize and analyze factors associated
with OB in pediatric SMPP patients, predictive factors predisposing
patients to OB development were not definitively identified. Therefore,
collection of additional clinical data is needed to further evaluate
possible predictors of later OB occurrence that would be used to inform
future clinical practice.
Acknowledgements: We thank the children and families who
graciously consented to participate in the bronchoscopy of SMPP children
in this study.