# The Deadly Masquerade: Unveiling the Fatal Facade of the Great Imitator

## TL;DR

This case report describes a rare bile duct condition that mimics more common diseases, highlighting diagnostic challenges.

## Contribution

The paper presents a rare case of IgG4-related sclerosing cholangitis that was initially mistaken for other conditions.

## Key findings

- A 67-year-old male was diagnosed with isolated IgG4-SC after being suspected of having cholangiocarcinoma or PSC.
- IgG4-SC can closely resemble other biliary diseases, making accurate diagnosis difficult.
- The case underscores the importance of considering IgG4-related disease in differential diagnoses of sclerosing cholangiopathy.

## Abstract

Sclerosing cholangitis (SC) is a fibroinflammatory condition that results in the progressive narrowing and destruction of bile ducts. It is generally classified into three distinct types: primary sclerosing cholangitis (PSC), secondary cholangitis, and immunoglobulin G4 (IgG4)-related cholangitis (IRC). IgG4-sclerosing cholangitis (IgG4-SC) is a rare entity characterized by inflammation and strictures within the biliary tree, arising from host-mediated immune responses. This condition represents the biliary manifestation of IgG4-related disease and may mimic other forms of sclerosing cholangiopathy, as well as cholangiocarcinoma. The clinical presentations of these diseases exhibit significant overlap, and diagnosis can be challenging. This case report discusses a 67-year-old male patient diagnosed with isolated IgG4-SC, who was initially suspected of having either cholangiocarcinoma or PSC.