# An Uncommon Case of Non‐Specific Interstitial Pneumonia (NSIP) Associated With Idiopathic Hypereosinophilic Syndrome (HES) Reversed by Mepolizumab

## TL;DR

A rare case of lung disease caused by an overactive immune response was successfully treated with a drug targeting a specific inflammation pathway.

## Contribution

This case highlights a novel association between HES and NSIP, and the effectiveness of mepolizumab in reversing lung disease.

## Key findings

- Non-Specific Interstitial Pneumonia (NSIP) was diagnosed in a patient with Hypereosinophilic Syndrome (HES).
- Treatment with mepolizumab led to near-complete reversal of the lung disease.
- The results suggest Th2-driven eosinophilic inflammation may play a role in some interstitial lung diseases.

## Abstract

Hypereosinophilic Syndrome (HES) represents a heterogeneous and complex group of disorders characterised by persistent blood and tissue eosinophilia, leading to progressive tissue damage and organ dysfunction. This spectrum includes both hematologic variants and non‐hematologic forms, either secondary to identifiable causes or idiopathic in nature. In this article, we describe a rare clinical presentation of HES manifesting primarily with pulmonary involvement, diagnosed as Non‐Specific Interstitial Pneumonia (NSIP). Remarkably, the interstitial lung disease showed near‐complete reversibility following targeted inhibition of the IL‐5 pathway with mepolizumab, highlighting the potential role of Th2‐driven eosinophilic inflammation in the pathogenesis of certain forms of interstitial lung disease.

In this article, we describe a rare clinical presentation of Hypereosinophilic Syndrome (HES) manifesting primarily with pulmonary involvement, diagnosed as Non‐Specific Interstitial Pneumonia (NSIP). Remarkably, the interstitial lung disease showed near‐complete reversibility following targeted inhibition of the IL‐5 pathway with mepolizumab, highlighting the potential role of Th2‐driven eosinophilic inflammation in the pathogenesis of certain forms of interstitial lung disease.