Encephalitis, High-Grade Atrioventricular Block, Acute Kidney Injury, and Hepatitis Following Atezolizumab Therapy: A Complex Case of Sequential Multiorgan Immune Checkpoint Inhibitor-Related Adverse Events.

Immune checkpoint inhibitors (ICIs) can cause serious toxicities due to widespread immune activation. We report the case of a 49-year-old man with lung cancer who presented with confusion and seizures 16 days after receiving atezolizumab. Investigations were unrevealing of a cause. Immunotherapy-related encephalitis was suspected, given the temporal association between symptoms and atezolizumab infusion. Despite treatment with antimicrobials and methylprednisolone, the patient developed ventricular standstill requiring cardiac pacing. Although neurology and cardiac rhythm improved with high-dose methylprednisolone and pacemaker insertion, the patient developed hepatitis and acute kidney injury (AKI) during steroid tapering, which resolved with re-escalation. This case highlights a potential life-threatening multiorgan dysfunction that can complicate ICI therapy. While established toxicity phenotypes present with synchronous multiorgan involvement, atypical cases may present with sequential organ involvement that can pose significant diagnostic challenges. This reinforces the need for vigilance and early multidisciplinary team coordination to ensure timely diagnosis and good outcomes.