Lambert-Eaton myasthenic syndrome (LEMS) in a patient with lung cancer under treatment with pembrolizumab: a case study

Abstract

Pembrolizumab is an immune checkpoint inhibitor (ICI) against the programmed death-1 receptor. Herein, we introduce a rare adverse effect during using pembrolizumab. We present the case of an 80-year-old man with biopsy-proven unresectable double primary squamous cell carcinoma and large cell neuroendocrine carcinoma of the lung. After using pembrolizumab for 10 months, he complained of muscle weakness of both upper and lower extremities. In a nerve conduction study, the repetitive nerve stimulation test in the abductor digiti minimi was diagnostic of Lambert-Eaton myasthenic syndrome (LEMS): low in the amplitude of compound muscle action potential (1.4 mV), 28.6% decrement in the 5-Hz stimulation, and 579% increment in the 50-Hz stimulation. The disease did not progress after the discontinuation of pembrolizumab, even without any anti-cancer treatment for 12 months. We believe our clinical experience of this rare and unexpected adverse effect should be shared.

Keywords:

• Immune checkpoint inhibitor
• immune-related adverse event
• Lambert-Eaton myasthenic syndrome
• pembrolizumab
• autoimmune

Disclosure statement

No potential conflict of interest was reported by the authors.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors contributions

CHM provided guidance to manage the clinical situation, JHL was a major contributor to writing the manuscript. CHM was the main physician for the patient and supervised the writing of the manuscript. DY examined and tested the neurological function of the patient in this case study and wrote the neurological aspects of the manuscript. YL guided the autoimmune antibody test and its clinical interpretation. All authors reviewed and edited the manuscript and approved the final manuscript.