Abstract

Mounier-Kuhn syndrome, or tracheobronchomegaly, is a rare clinical and radiologic condition characterized by marked tracheobronchial dilation and recurrent lower respiratory tract infections. Diagnosis is typically accomplished with the use of computed tomography and bronchoscopy, as well as pulmonary function testing. Patients may be asymptomatic; however, symptoms can range from minimal with preserved lung function to severe respiratory failure. Therapy, if any, is supportive but minimal. Surgery rarely has a place in the treatment of Mounier-Kuhn syndrome.

Herein, we report the case of a 58-year-old man with chronic obstructive pulmonary disease who had a chronic cough, increased sputum production, and chest pain. Thoracic computed tomography showed tracheal dilation (diameter, 34 mm) and multiple diverticula in the posterior region of the trachea. Fiberoptic bronchoscopy revealed enlarged main bronchi, the dilated trachea, and prominent tracheal diverticula. Pulmonary function testing disclosed impaired respiratory function. Histopathologic examination of biopsy specimens from the bronchi and the tracheal wall supported the diagnosis of Mounier-Kuhn syndrome. The patient was released from the hospital and his condition was monitored for 2 years, during which time he developed no lower respiratory tract infections.

Regardless of radiologic findings that suggest recurrent lower respiratory tract infection, we recommend that Mounier-Kuhn syndrome be considered in the differential diagnosis.

Mounier-Kuhn syndrome, or tracheobronchomegaly, is a rare clinical and radiologic condition. It is characterized by distinct dilation of the trachea and bronchi and by recurrent lower respiratory tract infections (LRTIs).^1–4 The syndrome was first described by Mounier-Kuhn in 1932,⁵ and fewer than 100 cases have been reported in the medical literature.⁴ The cause of the condition is not clearly understood; however, in biopsy studies, congenital atrophy has been observed in the smooth muscle and elastic tissue of the trachea and main bronchi. Bronchial and tracheal diverticula can also accompany tracheobronchomegaly.^1–4

Herein, we report the case of a patient who was diagnosed with Mounier-Kuhn syndrome with tracheal diverticula, and we discuss the case in the context of the medical literature.

Case Report

In August 2007, a 58-year-old man presented at our clinic with a chronic cough, increased sputum production, and chest pain. He had been diagnosed earlier with chronic obstructive pulmonary disease (COPD), for which he was being treated. He had no family history of COPD. He worked as an iron welder, and he had smoked 45 packs of cigarettes a year until 6 years previously.

A chest radiograph showed an enlarged tracheal diameter and areas of emphysema in both lungs. A physical examination revealed enlargement in the front-to-back chest diameter, and clubbing. Auscultation disclosed widespread rhonchi in both hemithoraces and prolonged expiration. Notable results of laboratory studies were an elevated erythrocyte sedimentation rate (47 mm/hr) and leukocytosis (total leukocytes, 11.8 ×10⁹/L). Pulmonary function testing revealed a forced expiratory volume in 1 sec (FEV₁) of 2.03 L (58%), a forced vital capacity (FVC) of 2.39 L (55%), and FEV₁/FVC of 105%.

Thoracic computed tomography (CT) showed interstitial thickening in both lungs, emphysematous changes in both lung apices, consolidation in the middle lobe of the right lung, and bronchiectasis in the left lower lobe. The CT images revealed a tracheal diameter of 34 mm and multiple tracheal diverticula between the cartilage rings. The internal diameters of the right and left main bronchi were dilated to 29 mm and 28 mm, respectively (Fig. 1A).

Fiberoptic bronchoscopy revealed tracheal dilation and diverticula in the posterior region of the tracheal wall (Fig. 2A) and enlargement of both main bronchi. Biopsy specimens from the bronchi and tracheal wall were examined histochemically with Verhoeff elastic stain; the loss of elastic fibers around the respiratory tract was almost complete in some areas. On the basis of these findings, the patient was diagnosed with Mounier-Kuhn syndrome and was discharged from the hospital after 7 days of therapy with oral levofloxacin (750 mg/d). His condition and medical therapy for COPD were monitored for 2 years, during which time he developed no LRTI. Neither enlargement nor infection was detected in the tracheal diverticula in CT images taken in November 2009 (Fig. 1B) or upon subsequent flexible bronchoscopy (Fig. 2B).

Discussion

Mounier-Kuhn syndrome is characterized by distinct tracheobronchial dilation that is due to atrophy of the muscular and elastic tissues in the trachea and main bronchial wall. It is more common in men and is typically diagnosed in the 3rd or 4th decades of life. The clinical presentation varies widely, from minimal disease in which lung function is preserved to severe respiratory failure and death. Involvement occurs at different levels, from the trachea down to the 4th bronchial branch.^1–7 Although its cause is not fully known, tracheobronchomegaly is reportedly linked to familial susceptibility and is perhaps inherited through an autosomal recessive mechanism. Cases are often sporadic.⁶

Mounier-Kuhn syndrome has 3 subtypes. In type 1, there is a slight symmetric dilation in the trachea and main bronchi. In type 2, the dilation and diverticula are distinct. In type 3, diverticular and saccular structures extend to the distal bronchi.⁴ The main problems associated with this disease are ineffective cough consequent to pathologic dilation in the tracheobronchial tree and the impairment of mucociliary activity. These cause difficulty in expectorating secretions and lead to recurrent LRTIs.⁶ The symptoms of Mounier-Kuhn syndrome are nonspecific. In the absence of infection, the disease can develop asymptomatically. Bronchiectasis and LRTIs are clinically prominent, and recurrent pneumonia and fibrosis can develop.^3,4

Diagnosis is often made by using CT, through which abnormally large air passages are detected. In adults, the diagnostic criteria are diameters of the trachea, >30 mm; of the right main bronchus, 20 mm; and of the left main bronchus, 18 mm.^7–9 Upon pulmonary function testing, decreased bronchial flow speed, increased tidal volume, and dead spaces may be observed. Bronchoscopy can detect the pathologic processes that affect the tracheobronchial structures—specifically, dilation in the trachea and main bronchi during inspiration, and constriction and even collapse during expiration and coughing.^1,4

Connective-tissue diseases, ataxia-telangiectasia, ankylosing spondylitis, Ehlers-Danlos syndrome, Marfan syndrome, Kenny-Caffey syndrome, Brachmann-de Lange syndrome, and cutis laxa (elastolysis) are also associated with secondary tracheobronchial enlargement.^7,10 All of these conditions should be considered in the differential diagnosis.

Asymptomatic patients require no specific treatment. Cessation of smoking is highly beneficial, as is minimizing exposure to industrial and occupational irritants and pollutants. In symptomatic patients, therapy is supportive but is limited to respiratory physiotherapy for clearing secretions and to antibiotic use during infectious exacerbations.^4,10 Although tracheal stenting has been helpful in severe cases, surgery is rarely performed because of the diffuse nature of the disease. Lung transplantation provided no proved benefit in regard to the risk of morbidity and death.^7,10

From our experience with this patient, we recommend that Mounier-Kuhn syndrome be considered in the differential diagnosis, regardless of radiologic findings that suggest recurrent LRTIs.

Footnotes

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