Case Report of Delayed Encephalopathy From Pembrolizumab

Area of Science:

• Neuroscience
• Oncology
• Immunology

Background:

• Pembrolizumab, an immune checkpoint inhibitor (ICI), treats advanced cancers but can cause encephalopathy, a severe immune-related adverse event.
• Immune-related adverse events from ICIs typically manifest early in treatment, with late-onset presentation being exceptionally rare.

Observation:

• A 70-year-old female with metastatic endometrial cancer, treated with pembrolizumab for 19 months, developed progressive neurological symptoms.
• The patient presented with generalized weakness evolving into confusion, delusions, and hallucinations.

Findings:

• Encephalopathy was diagnosed after excluding other potential causes through extensive blood, cerebrospinal fluid, and imaging tests.
• Neurological status improved significantly following treatment with high-dose glucocorticoids and intravenous immunoglobulin.

Implications:

• Pembrolizumab-induced encephalopathy can present with a significant delay, challenging typical timelines for immune-related adverse events.
• This case underscores the importance of considering delayed ICI-induced neurological toxicity in patients presenting with unexplained encephalopathy, even after extended treatment durations.