Mounier-Kuhn syndrome (MKS) or congenital tracheobronchomegaly is a chronic and rare airway morbidity associated with recurrent respiratory infections and characterized by dilation of the trachea and the main bronchi [1]. This disease was first clinically described by Mounier-Kuhn in 1932 [2]. The estimated prevalence of this syndrome in patients with pulmonary symptoms is between 0.4% and 1.6%, and it mostly affects the male gender [1,3-5]. Diagnosis of the MKS is frequently made in the third or fourth decade of life when the symptoms are more exuberant [6]. Histological alterations seen in the disease can be used to explain structural defects such as tracheobronchomalacia (TBM), saccular diverticula between cartilages, and bulging and dilation of the trachea and bronchi [1,7].

The predominant signs and symptoms of the disease include coughing, purulent and abundant expectoration, digital clubbing, dyspnea, snoring, wheezing, and recurrent respiratory infection [1]. The disease could be associated with other comorbidities such as gastroesophageal reflux disease, chronic obstructive pulmonary disease, bronchiectasis, and obstructive sleep apnea/hypopnea syndrome (OSAHS) [1,8-12].

Some of the observed symptoms could be a consequence of TBM occurrence in some patients, which is defined by more than 50% collapse of the intrathoracic trachea and bronchi [13-16]. The main clinical consequences of TBM are obstruction to expiratory airflow; secondary air trapping; decrease in the effectiveness of cough and bronchial hygiene; and facilitation of conditions that promote microorganism colonization, leading to recurrent respiratory infection [4,13].

Despite the patient’s normal pulmonary function, the occurrence of obstructive ventilatory disorder is not uncommon [1,17-19]. Thorax computed tomography (CT) shows dilatation of the trachea and the right and left main bronchi [4,20,21]. Tracheobronchial diverticula, bronchiectasis, air trapping, and emphysema are common findings, suggesting involvement of the small airways [1,7,10,11,22-26]. Bronchoscopy is the gold standard examination for TBM diagnosis [12,14-16,26].

Since TBM is a rare and poorly studied disease, there is no consensus on a specific therapy. Therapeutic management includes inhaled bronchodilators, corticosteroids, hypertonic solution, and mucolytic agents. Some complementary tools used for disease management include noninvasive positive respiratory pressure, vaccination, respiratory physiotherapy, and pulmonary rehabilitation [1,27-29]. Continuous positive airways pressure (CPAP) support has been reported as an option for the treatment of tracheomalacia [5,15,30]. The rationale for using positive pressure in TBM is to recover the patency of the collapsed airways, thereby reducing airflow obstruction and promoting sputum clearance.

Previous experience has shown that CPAP can reduce symptoms, infections, and morbidity/mortality caused by TBM [5,15,31-33]. Additionally, it is an effective therapy in patients diagnosed with concomitant OSAHS [34-36]. This study has two main objectives. First, we aim to confirm the presence of tracheal collapse and the main bronchi of patients with MKS through respiratory endoscopy. Second, we will attempt to optimize the pressure with the CPAP approach to reduce or reverse the pathological consequences of the syndrome on the ventilatory pattern. We also will investigate the prevalence of OSAHS in this population. We hypothesize that maintenance of greater patency of airways could improve pulmonary ventilation for a longer time, reduce symptoms, and improve the quality of life of these patients.

The project was submitted to the institutional review board on January 24, 2017, and approved on February 2, 2017 (Brazilian Research database number CAAE 64001317.4.000.0068). The project was registered in ClinicalTrails.gov (NCT03101059) on March 23, 2017. This protocol is a doctorate project. Patient evaluations started in April 2018. Planned recruitment is based on volunteers’ availability and clinical stability, and the interventions will be conducted at least once a month and completed at the end of 2020. A preliminary analysis of each case will be performed after each intervention, but detailed results are expected to be closed in the first quarter of 2021. We plan to publish 3 papers on this project. The proposed schedule for publication of the papers is as follows: the intervention protocol in 2019-2020; literature review about the concept of tracheobronchomalacia and airway collapse according to diverse uses ways to measure them and their definition in 2020; and results of the presence of tracheal collapse and the main bronchi of patients with MKS, through respiratory endoscopy and optimum positive pressure with CPAP that reduces or reverse it, in 2021.

Thus far, the main finding of this study is the identification of the progressive increase in the degree of pressure that can reverse the collapse of the trachea and bronchi and stabilize the airway.

MKS or congenital TBM is a rare and poorly studied disease. It has a wide spectrum of signs and symptoms and can have a great impact on the quality of life. Dyspnea, accumulation of secretions in the airways, bronchiectasis, and recurrent respiratory infections increase the morbimortality of the disease.

There is no consensus on the best treatment. In general, measures extrapolated from other pulmonary pathologies, such as those employed in chronic obstructive pulmonary disease and bronchiectasis, are used for therapeutic management. Among the specific treatments currently available, we want to highlight the endotracheal and endobronchial prosthesis and tracheobroncoplasty surgery. However, both approaches have limited results and are associated with frequent complications.

There is a rationale for the use of positive pressure. The use of positive pressure could maintain the patency of the collapsed airways, thereby providing a “pneumatic stent,” which in turn could reduce airflow obstruction and promote mobilization of secretions within the airways. However, no study protocol has been performed to test this hypothesis.

The goal of this study is to assess if positive pressure with CPAP can be applied to reduce the extent of airway collapse and improve ventilation in MKS patients with tracheobronchomalacia. At the same time, we will evaluate the prevalence of OSAHS, a related and frequently occurring comorbidity that contributes to the worsening quality of life of patients with MKS.