Pembrolizumab-induced simultaneous and multiple immune-related adverse events including myasthenia gravis, myositis, hepatitis, and pityriasis lichenoides in a non-small cell lung cancer patient.

Pembrolizumab, an immune checkpoint inhibitor (ICI) targeting the programmed cell death protein 1 (PD-1) receptor on T cells, enhances the immune system's ability to recognize and attack cancer cells. However, immune-related adverse events (irAEs) may arise, necessitating careful monitoring during treatment. Here, we present the case of a 47-year-old woman who developed multiple irAEs following pembrolizumab therapy. Initially diagnosed with Stage IIIB non-small cell lung cancer, she underwent chemotherapy followed by concurrent chemoradiotherapy. After two years of monitoring, progression of disease was observed, and pembrolizumab was initiated as second-line chemotherapy. Shortly thereafter, she presented with left-sided ptosis and weakness in both upper and lower extremities. Diagnostic evaluation, including a tensilon test and laboratory findings, confirmed with myositis, hepatitis, and myasthenia gravis. Treatment with steroids and neostigmine led to marked clinical improvement. Two months later, the patient developed additional dermatological symptoms, including rash and pruritus. Skin biopsy confirmed a diagnosis of pityriasis lichenoides. She is currently receiving antihistamines therapy, with no further exacerbation. This case underscores the importance of recognizing and promptly managing irAEs associated with ICIs to ensure patient safety and treatment efficacy.