# Pulmonary Langerhans Cell Histiocytosis: An Unusual Differential for a Solitary Lung Nodule

## TL;DR

This case study describes a rare instance of pulmonary Langerhans cell histiocytosis presenting as a solitary lung nodule in a smoker, highlighting the importance of proper diagnosis.

## Contribution

The paper presents a rare clinical case of isolated lung nodule caused by LCH and emphasizes the need for immunostaining in diagnosis.

## Key findings

- The patient's lung nodule was diagnosed as LCH through biopsy and immunostaining.
- The nodule decreased in size after the patient reduced smoking.
- Immunostaining is critical to differentiate LCH from malignancy in isolated lung nodules.

## Abstract

Pulmonary Langerhans cell histiocytosis (LCH) commonly presents as bilateral reticulonodular and cystic lung changes on chest imaging. Isolated lung nodule presentation is rare. Case Presentation. Our patient was an elderly male and an active smoker, who was referred to the pulmonology clinic for an incidental 19 mm lung nodule seen on a chest CT scan. A CT-guided transthoracic needle biopsy was performed to rule out malignancy. The biopsy sample showed marked inflammatory infiltrate with abundant eosinophils and epithelioid histiocyte-like cells suggestive of Langerhans cell histiocytosis. Antibodies against CD1a and Langerhans were positive which confirmed the diagnosis. During follow-ups, the patient had reduced smoking, and the lung nodule had decreased in size to 14 mm.

An isolated lung nodule in a patient with a smoking history always warrants a malignancy workup. Characteristic pathological findings with immunostaining are necessary to differentiate pulmonary LCH in these cases. Failure to perform immunostaining in such cases may lead to missing this vital diagnosis.