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

## TL;DR

A 62-year-old man with chronic lung symptoms was diagnosed with rare right middle lobe syndrome, successfully treated after identifying a mucus plug and infection.

## Contribution

This case highlights the importance of considering RMLS in adults with chronic pulmonary symptoms and localized lobe collapse.

## Key findings

- A mucus plug was identified and removed from the right middle lobe, with no endobronchial obstruction found.
- Streptococcus pneumoniae was cultured and treated successfully with ceftriaxone, leading to clinical and radiologic improvement.
- Pathology showed mild chronic inflammation without malignancy, confirming a non-cancerous cause for the symptoms.

## Abstract

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.