A Case of Right Middle Lobe Syndrome: A Rare Diagnosis Behind Chronic Pulmonary Symptoms.

Right middle lobe syndrome (RMLS) is an uncommon pulmonary condition characterized by recurrent or chronic atelectasis or infection of the right middle lobe, often due to either obstructive or non-obstructive mechanisms. We present the case of a 62-year-old male with a history of chronic obstructive pulmonary disease (COPD), prediabetes, and prior tobacco use, who presented with mid-sternal chest pain and a chronic dry cough. Imaging revealed right middle lobe collapse without endobronchial obstruction on bronchoscopy. A mucus plug was identified and removed, revealing edematous mucosa but no visible lesions. Cultures grew Streptococcus pneumoniae sensitive to ceftriaxone, while acid-fast bacilli (AFB) and fungal cultures were negative. Pathology demonstrated mild chronic inflammation with no malignancy. The patient responded well to antibiotics and inhaler therapy, with radiologic evidence of partial resolution on follow-up imaging. This case highlights the diagnostic challenges of RMLS in adults and underscores the importance of considering this rare entity in patients with chronic pulmonary symptoms and localized lobe collapse. Early bronchoscopy and appropriate treatment can lead to clinical and radiologic improvement.