Mounier-Kuhn syndrome is a rare clinical and radiologic entity characterized by pathologic dilatation of the trachea and bronchi.1 It is a form of expiratory central airway collapse characterized by the softening of the airway wall cartilaginous structures and is usually associated with bronchiectasis and lower respiratory tract infection. We present the radiologic, spirometric, and microbiologic findings and functional impairment of the trachea observed during bronchoscopy in a patient with Mounier-Kuhn syndrome.
A 73-year-old, life-long male nonsmoker was admitted to the hospital with the complaints of productive cough and dyspnea. He had been diagnosed with and treated for chronic obstructive pulmonary disease. He had also developed recurrent lower respiratory tract infections. Physical examination showed bilateral fine end-inspiratory crackles and expiratory bronchi. Purulent sputum was present. Blood analysis was normal. Chest roentgenogram showed bilateral hyperlucent lung, dilated trachea, and bilateral lower lobe bronchiectasis (Fig. 1). Spirometry showed forced expiratory volume in 1 second, 32%; forced vital capacity (FVC), 46%; and forced expiratory volume in 1 second/FVC, 53%, without any improvement with bronchodilators. In addition, a saw-tooth appearance was observed on the flow-volume loop (Fig. 2). We performed computed tomographic (CT) scans of the thorax that showed marked dilatation of the trachea, right and left main bronchi with inner diameters of 48, 29, and 31 mm, respectively, and bilateral bronchiectasis (Fig. 3). Pseudomonas aeruginosa was isolated on sputum culture. We performed a flexible bronchoscopy (FB) to detect the functional impairment of the Mounier-Kuhn syndrome. The bronchoscopy showed the dilated trachea during inspiration. Dynamic collapse of the trachea during expiration was evident with the luminal collapse of more than 50% (Fig. 4).
The clinical, radiologic, and endoscopic features of congenital tracheobronchomegaly were first described in 1932 by Mounier and Kuhn; the syndrome is characterized by expiratory central airway collapse and airflow limitation because of the excessive narrowing of the central airways during expiration.2 The etiology is uncertain. It may be caused by the lack of smooth muscle and elastic connective tissues in the trachea and main bronchi.3,4 Furthermore, dilated airways lead to an inefficient cough mechanism with impairment of mucociliary clearance. Recurrent infections lead to bronchiectasis and recurrent infections, as seen in our case.5 The patients usually present in the third or later decades of life.6
The most common symptom is purulent sputum production because of recurrent respiratory tract infections. Dyspnea, cough, difficulty in clearing secretions, recurrent bronchitis, pneumonia, and respiratory failure have been reported in patients with the Mounier-Kuhn syndrome.7 These are nonspecific symptoms and are similar to those in patients with chronic lung disease. In addition, many patients are diagnosed months or years after being treated for asthma or chronic obstructive pulmonary disease, as seen in our patient.8
Pulmonary functions may suggest a diagnosis. The flow-volume loop patterns on a spirogram may suggest compression of the central airways. The saw-tooth pattern, as noted on flow-volume loop during expiration in our patient, could also be present. Flow oscillation or saw-tooth appearance is defined as a reproducible sequence of alternating decelerations and accelerations of flow.2 Although this sign has been reported, we did not find a saw-tooth appearance consistently in the spirography images in reported cases.
The diagnosis is made with radiographic findings and the CT is a gold standard. The transverse diameter of the trachea, and the right and left main bronchi greater than 30, 24, and 23 mm, respectively, establishes the diagnosis.8 In this case, they were 48, 29, and 31 mm for the trachea and the right and left main bronchi, respectively.
FB is considered by some to be the gold standard for diagnosis. We performed the bronchoscopy to show the main pathologic mechanism of the Mounier-Kuhn syndrome. FB showed the airway collapse of more than 50% during expiration compared with inspiration.
In this case, P. aeruginosa was isolated from the sputum culture. This microorganism is one of the most commonly grown microorganisms in patients with the Mounier-Kuhn syndrome. It is also one of the most common microorganisms in patients with chronic bronchitis and bronchiectasis.8,9
Treatment of Mounier-Kuhn syndrome is supportive. Inhaled bronchodilators, postural drainage, and antibiotics can help to relieve symptoms in selected patients.10 The symptoms were improved with a bronchodilator and antibiotic treatment in our case. Tracheal stenting has proved beneficial in patients with the Mounier-Kuhn syndrome and multiple tracheal diverticuli.11 Several cases of lung transplantation have been reported in the literature with no proven benefit in mortality.12,13
The Mounier-Kuhn syndrome has a clinical presentation similar to that of chronic bronchitis and bronchiectasis. It can easily be diagnosed and distinguished from chronic bronchitis with characteristic radiologic and bronchoscopic findings, and a detailed history of symptoms.
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