# When flames hit the brain, and the spark is far away: the role of PET-CT in diagnosing neurological Erdheim-Chester disease

## TL;DR

This paper discusses how PET-CT can help diagnose neurological Erdheim-Chester disease, a rare disorder that affects the brain and is hard to detect.

## Contribution

The paper highlights the role of PET-CT in guiding biopsies and interpreting results for targeted therapy in neurological Erdheim-Chester disease.

## Key findings

- PET-CT is useful in identifying neurological involvement in Erdheim-Chester disease.
- Biopsy findings combined with immunohistochemistry can guide targeted therapies like vemurafenib for BRAF V600E mutations.

## Abstract

Erdheim-Chester disease (ECD) is a rare histiocytic disorder that poses diagnostic and therapeutic challenges. Neurological manifestations are characterized by involvement of the meninges, brainstem, and/or cerebellum, and the differential diagnoses include sarcoidosis, IgG4 related disorders, autoimmune encephalitis, and high-risk syndromes. While present in a significant proportion of cases, neurological involvement is a predictor of mortality and may be the sole manifestation of the disease. In this paper, we discuss recent updates in histiocytic disorders and complementary diagnostic approaches, including positron-emission tomography-computed tomography (PET-CT), as guidance for biopsy in patients with neurological symptoms. Additionally, we explore how clinicians can interpret biopsy findings in conjunction with immunohistochemistry to guide targeted therapies, such as vemurafenib, for
BRAF
V600E mutation.