A 46-year-old man with tracheomegaly, tracheal diverticulosis, and bronchiectasis: Mounier-Kuhn syndrome.

Lower respiratory tract infection is one of the common causes of morbidity in India which is occasionally undiagnosed. In this regard tracheobronchomegaly is one of those conditions which masquerade as chronic bronchitis and bronchiectasis and are usually undiagnosed. It is a well-defined clinical and radiologic entity characterized by marked dilatation of the trachea and the central bronchi and is frequently associated with recurrent lower respiratory tract infection. Tracheobronchomegaly has been described by a variety of names, including Mounier-Kuhn syndrome, tracheal diverticulosis, tracheobronchiectasis, tracheocele, tracheomalacia, and tracheobronchopathia malacia.

INTRODUCTION

Tracheobronchomegaly or Mounier-Kuhn syndrome is a rare disorder characterized by marked dilatation of the trachea and main bronchi, bronchiectasis, and patient usually presents with recurrent respiratory tract infections.

The etiology of this disorder is uncertain and the clinical presentation is variable. For an adult, any diameter of the trachea, right main bronchus, or left main bronchus that exceeds 3.0, 2.4, or 2.3 cm, respectively on a standard chest radiograph or bronchogram is diagnostic for it.

CASE REPORT

A 46-year-old nonsmoker, nonalcoholic man, clerk by occupation, attended with complaints of chronic cough with mucoid expectoration for last 15 years, which became purulent during infectious exacerbations, occassionally with blood-stained sputum. He had 2--3 exacerbations lasting for 1 to 2 weeks annually. He also had breathlessness on exertion since 2--3 years with marked seasonal variation which was relieved on antibiotic and routine bronchodilator. There was no history of fever, wheeze, chest pain, or weight loss. No other associated comorbid conditions were present (diabetes, hypertension, hyperlipidemia, or immunosuppresion). There was no significant admission history and family history was unremarkable for any other connective and autoimmune disease. On admission his vitals were stable and arterial blood gas values were under normal limit. On physical examination the patient was well nourished, thin built with symmetrical finger clubbing. Clinical respiratory examination revealed bronchial breathing bilaterally at apices and inspiratory crackles at the lower third of both lung fields. Sputum and tracheal aspirate were negative for bacterial, mycobacteria, and other atypical organisms. Baseline laboratory tests revealed increased erythrocyte sedimentation rate (24 mm/h) and C-reactive protein level (28 mg/l; normal= 0-20 mg/l). The rheumatoid factor and CCP (anticyclic citrillunated peptide) were normal. Antinuclear antibody levels were mildly raised but there was no characteristic immunoflouroscence pattern. His forced expiratory volume in 1 second, diffusion capacity, forced vital capacity, total lung capacity, and residual volume were 33%, 33%, 52%, 109%, and 20% of the predicted value respectively.

A chest radiograph revealed upper lobe bronchiectasis [Figure 1] while the chest CT scan showed tracheomegaly with transverse diameter of the trachea, right, and left main bronchus of 36 mm, 28 mm, and 24 mm, respectively. Many diverticular out pouchings were present from the trachea to the main bronchi. There was also evidence of cystic bronchiectasis involving both upper lobes [Figure 2]. On fiber optic bronchoscopy (FOB) several openings in the posterior and lateral wall of trachea and main bronchus were seen and some of which could be easily penetrated by the tip of bronchoscope. In these openings, we could identify collection of copious amounts of mucoid secretion [Figure 3].

Figure 1

CXR showing bronchiectasis and tracheomegaly

Figure 2

CT showing diverticular out pouchings and bronchomegaly

Figure 3

FOB showing roomy airways with mucoid secretions

DISCUSSION

Mounier-Kuhn syndrome (MKS) is a rare disorder of unknown cause that is characterized by atrophy of the elastic and smooth muscle of the tracheobronchial tree, tracheobronchomegaly (TBM), and severe bronchiectasis. There is male predominance, and patients usually present in adult life.

The condition was first recognized at autopsy by Czyhlarz in 1897, but it was not until 1932 that Mounier-Kuhn associated the endoscopic and radiographic appearance of the markedly enlarged airway with recurrent respiratory tract infection. Tracheobronchomegaly is believed to be rare. Till date, only 82 cases have been reported in the literature. However, some patients with tracheobronchomegaly may be totally asymptomatic and are not detected, whereas those with symptoms frequently are overlooked if chest radiographs alone are used for diagnosis.[12]

The cause of tracheobronchomegaly in our case is unknown and the patient also denied any evidence of connective tissue diseases. Although the association of this condition with Ehlers-Danlos syndrome reported in adults and with acquired cutis laxa in children may suggest a congenital defect in connective tissue as the basis for tracheobronchomegaly; most cases, however, presented in the third or later decades of life and showed no evidence of other connective tissue disorders.

Tracheobronchomegaly is, therefore, believed to be an acquired rather than a developmental anomaly.[3] Disorders such as sarcoidosis, usual interstitial pneumonia, and cystic fibrosis, which cause severe fibrosis of the upper lobes, may also exert sufficient tracheal traction to result in tracheal enlargement. Certain other conditions such as Marfan syndrome, Ehlers-Danlos syndrome, Kenny-Caffey syndrome, ataxia-telangiectasia, connective tissue diseases, Brachmann-de Lange syndrome, Bruton-type agammaglobulinemia, ankylosing spondylitis, cutis laxa, and light chain deposition disease are also associated with secondary tracheobronchial enlargement.[45]

In our case diagnosis is established on the basis of radiologic findings of TBM, diverticulosis, outpouching of the airway wall on lateral chest radiography, and characteristic endoscopic findings. Here the dilatation of trachea and central bronchi was associated with an abrupt transition to a normal caliber of the peripheral airways as well which was well diagnosed by a standard chest radiograph/bronchogram. The upper limits of the mean plus three standard deviations for diameter of trachea, right main bronchus, and left main bronchus are 3.0, 2.0, and 2.3 cm, respectively. The diameters in the present case were 3.6, 2.8, and 2.4 cm, respectively, fulfilling the diagnostic criteria for tracheobronchomegaly.[67]

TBM is a condition for which no effective therapy exists and usually it is mainly supportive. Symptomatic patients with airway collapse might require endobronchial stenting. Treatment is directed to minimizing the damage resulting from stasis and infection, and general supportive therapy, e.g., bronchodilators.[1]