Primary angiitis of the central nervous system is an extremely rare diagnosis, with an incidence of 2.4 cases per 1,000,000 person-years. The exact cause of PACNS remains unknown, and typically cases present with a long prodrome. It is a diagnosis of exclusion, and various infectious, autoimmune, and malignant processes must be excluded prior to final diagnosis. Given the rarity of this condition, there is often a delay in diagnosis that can range from 6 to 23 months. It is imperative that all clinical providers be aware of this diagnosis when managing patients who present with insidious and non-specific neurological symptoms. We present a case of PACNS that responded well to a therapeutic regimen of high-dose steroids and cyclophosphamide.

Immune checkpoint inhibitors (ICIs) improve outcomes across malignancies but can cause immune-related adverse events (irAEs), notably myocarditis, with case-fatality up to 50%.