Mounier - Kuhn Syndrome

By Dr Deepu

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.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.

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. 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.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.

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.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.

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.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.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.

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