INTRODUCTION: A sixty-two year old African American male presented to our institution with several years of dyspnea on exertion and minimally productive cough. Rales on exam, hypoxemia, as well as weight loss prompted suspicion for an underlying interstitial lung disease. Pulmonary function studies showed preserved spirometry. Chest radiograph and computed tomography however showed massive tracheobronchomegaly with cystic bronchiectasis consistent with the diagnosis of Mounier-Kuhn syndrome.
CASE PRESENTATION: A sixty-two year old male with a 15 pack-year history of remote tobacco use presented to our institution with dyspnea on exertion, cough, and progressive weight loss of 10 kg over the last several years. He had cough productive of clear to yellow sputum, usually in the mornings. He denied hemoptysis, rhinitis, post-nasal drip, or gastro-esophageal reflux. His past medical history is significant for hypertension, although he has not seen a physician in many years. He worked as a lab and veterinary technician. There was no family history of lung disease. On examination, he was tachycardic at 126 beats per minute, and hypoxic with 84% oxygen saturation. He appeared malnourished and cachectic, with a body mass index of 15.4 kg/m^2. On auscultation, there were bilateral basilar rales and some inspiratory squeaks. Marked digital clubbing was present, but there were otherwise no signs of pulmonary hypertension or heart failure. The spirometry, including the inspiratory and expiratory flow-volume loops, showed no abnormalities. On body plethysmography, the total lung capacity was normal, but mild air trapping was present. Most notably, the diffusing capacity for carbon monoxide was severely reduced at 33% of predicted. Arterial blood gases showed a PaO2 of 58 mmHg on room air. Chest x-ray showed marked bronchial cystic changes diffusely in both lungs. A high resolution CT of the chest confirmed tracheobronchomegaly and severe extensive cystic bronchiectasis. Large airway diverticuli were also visible by CT. The imaging findings were consistent with a diagnosis of Mounier-Kuhn syndrome.
DISCUSSION: Mounier-Kuhn Syndrome was first described in 1932, with the main feature being the presence of tracheobronchomegaly. Fewer than 100 cases have been reported in the medical literature. Diagnostic criteria include a right mainstem bronchus diameter greater than 2.4 cm, left main bronchus greater than 2.3 cm, and trachea diameter greater than 3.0 cm. Several different subtypes have been described including symmetrical tracheal and bronchial enlargement, eccentric enlargement, and the presence of diverticuli extending to the distal bronchi. Histologically the muscularis propria is thinned with the longitudinal elastic fibers becoming atrophied. Symptoms can range from chronic cough to severe respiratory failure requiring mechanical ventilation. It can also be associated with connective tissue diseases such as rheumatoid arthritis, Elhers-Danos syndrome, and Cutis Laxa in children. Patients are often misdiagnosed as having bronchiectasis or chronic obstructive pulmonary disease. The spirometry often shows obstruction, but as demonstrated in this case, the spirometry and lung volumes can be normal despite radiographically advanced disease. We speculate that this results from the predominant involvement of the large airways, while sparing the distal small airways and lung elastic recoil. Thus, pulmonary function testing should be interpreted with caution in patients with severe tracheobronchomegaly or suspected Mounier-Kuhn syndrome.
CONCLUSIONS: To our knowledge, this is the first case of Mounier-Kuhn syndrome demonstrating such severe imaging findings with normal spirometry.
Reference #1 Woodring, John H. et al. Congenital Tracheobronchomegaly (Mounier-Kuhn Syndrome): A report of 10 cases and review of the literature. Journal of Thoracic Imaging, April 1991.
DISCLOSURE: The following authors have nothing to disclose: John Moss, Augustine Lee
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