Right middle lobe syndrome caused by eosinophilic mucoid impaction in adults

Right middle lobe syndrome (RMLS) is defined as a transient or recurrent, chronic collapse of the middle lobe of the right lung by certain pathologic conditions. RMLS is a relatively uncommon condition having multiple etiologies and various clinical presentations. Two patients were referred to Hallym University Sacred Heart Hospital, one for the treatment of coughing and the other for the treatment of pneumonia. A diagnosis of RMLS was identified through X-ray and computed tomography image evaluation for each condition. Bronchoscopy revealed mucus obstruction in the right middle lobe bronchus. Biopsy of the aspirated mucus showed mucus containing many eosinophils and Charcot-Leyden crystals. After removal of impacted mucus, clinical and radiological improvements were observed in both patients. Therefore, eosinophilic mucus impaction can be considered a potential cause of RMLS, irrespective of any underlying asthmatic symptoms.