Mounier-Kuhn Syndrome in an Elderly Male With Recurrent Pulmonary Infections

Abstract Introduction Mounier-Kuhn syndrome (MKS), or tracheobronchomegaly, is a rare congenital disorder characterized by marked dilation of the trachea and major bronchi, resulting from atrophy of the elastic and muscular tissues of the airway walls. Though typically diagnosed in younger adults, the condition can present later in life with recurrent respiratory infections and bronchiectasis, making timely diagnosis critical. Case Description 83-year-old male with a history of asthma, chronic obstructive pulmonary disease (COPD), obstructive sleep apnea, and atrial fibrillation on warfarin presented with worsening cough and dyspnea for over a week. Initially the patient was started on empiric IV antibiotics with findings of right lower lobe consolidation on chest radiograph. Further imaging with computed tomography of the chest showed extensive bronchiectasis with tracheobronchomegaly, multiple tracheal diverticula and bronchiectasis, prompting the concern for Mounier-Kuhn syndrome. The patient was managed with antibiotics, secretion mobilization therapies, and outpatient follow-up. Bronchoscopy and further invasive evaluations were discussed but ultimately deferred until cardiac clearance for comorbidities were obtained. The patient was subsequently discharged with resolution of CAP and appropriate cardiac, and pulmonology outpatient follow up. Discussion Mounier-Kuhn syndrome is a rare but important differential diagnosis in patients presenting with recurrent pulmonary infections and bronchiectasis. Etiology is thought to be due to congenital weakness/atrophy of the muscular and elastic tissue of the airways but is not fully understood. Cases have been linked to familial susceptibility, but literature reviews show rare cases of sporadic etiology. The diagnosis of MKS is made by CT, which demonstrates tracheal diameter >3 cm and right mainstem bronchus diameter of >2.4 cm and left mainstem bronchus diameter of >2.3 cm. The ensuing tracheobronchomegaly can cause central airway collapse by excessive dynamic airway collapse and tracheobronchomalacia. The symptoms of this disease are associated with ineffective cough consequent to pathologic dilation in the tracheobronchial tree and the impairment of mucociliary activity causing recurrent infections. While management focuses on supportive care, chest physiotherapy and antibiotics during exacerbations are helpful in reducing complications. Surgical interventions such as tracheal stenting can be considered in severe cases but is rarely performed due to the diffuse nature of this disease. This case adds to the growing recognition of MKS as a rare cause of bronchiectasis and recurrent infections in elderly patients.