# Early-Onset Ramsay Hunt Syndrome After Pembrolizumab Administration in a Patient With Lung Adenocarcinoma

## TL;DR

A patient with lung cancer developed Ramsay Hunt syndrome after receiving pembrolizumab, highlighting a rare but important side effect of immune checkpoint inhibitors.

## Contribution

This case report highlights RHS as a potential immune-related adverse event of pembrolizumab, possibly linked to non-HIV IRIS.

## Key findings

- A 64-year-old lung cancer patient developed RHS six days after pembrolizumab administration.
- Early treatment with valacyclovir and corticosteroids led to gradual recovery from severe facial paralysis.
- ICI-induced RHS is rare but should be considered in patients receiving immune checkpoint inhibitors.

## Abstract

Immune checkpoint inhibitors (ICIs) are associated with a broad spectrum of adverse effects referred to as immune-related adverse events (irAEs). Some infectious diseases can be precipitated by ICIs due to dysregulated inflammatory immune responses referred to as immune reconstitution inflammatory syndrome (IRIS), which were originally described in human immunodeficiency virus (HIV).

Here, we report a case of Ramsay Hunt syndrome (RHS) considered to have occurred as “non-HIV IRIS” after the administration of pembrolizumab. A 64-year-old man with stage IVb lung adenocarcinoma was treated with pembrolizumab as first-line chemotherapy. He presented with a headache in two days and right facial paralysis with some vesicles on the rash in the right external auditory canal six days after the administration. We diagnosed ICI-induced RHS and initiated valacyclovir and systemic corticosteroid therapy. The degree of facial paralysis was severe, but it recovered gradually.

Although ICI rarely causes RHS, clinicians should be aware of the possibility of RHS, as the prognosis of paralysis depends on early treatment.