Pembrolizumab-Induced Myositis Presenting with Ocular Symptom and Head Drop in a Patient with Positive Acetylcholine Receptor Binding Antibody

Kang, Minsung; Kim, Ye-ri; Park, Jin-Sung

doi:2026.44.4.339

J Korean Neurol Assoc > Volume 44(4); 2026 > Article

Case Report

Journal of the Korean Neurological Association 2026;44(4): 339-342. doi: https://doi.org/10.17340/jkna.2026.0030

항아세틸콜린수용체항체 양성 환자에서 안구 증상 및 머리 떨굼으로 발현한 펨브롤리주맙 유발 근육염

강민성¹, 김예리², 박진성¹

¹경북대학교 의과대학 칠곡경북대학교병원 신경과
²경북대학교 의과대학 면역학교실

Pembrolizumab-Induced Myositis Presenting with Ocular Symptom and Head Drop in a Patient with Positive Acetylcholine Receptor Binding Antibody

Minsung Kang MD¹, Ye-ri Kim PhD², Jin-Sung Park MD, PhD¹

¹Department of Neurology, School of Medicine, Kyungpook National University, Kyungpook National University Chilgok Hospital, Daegu Korea
²Department of Immunology, School of Medicine, Kyungpook National University, Daegu, Korea

Corresponding Author: Jin-Sung Park ,Tel: +82-53-200-2753, Fax: +82-53-200-3870, Email: neurojspark@gmail.com

Received: April 22, 2026 Revised: July 30, 2026 Accepted: August 10, 2026 Published online: November 1, 2026

Abstract

A 55-year-old man with malignant thymoma and pre-existing acetylcholine receptor antibodies developed ptosis and head drop after pembrolizumab treatment. Although recurrence of myasthenia gravis was initially suspected, markedly elevated creatine kinase levels and myopathic findings on electromyography supported immune checkpoint inhibitor (ICI)-induced myositis. This case highlights that ocular and respiratory symptom after ICI therapy should raise suspicion for ICI-induced myositis, even in acetylcholine receptor antibody-positive patients.

Key Words: Immune checkpoint inhibitor | Myositis | Myasthenia gravis