From Kidney to Brain: An Uncommon Severe Relapse of Myeloperoxidase Anti-Neutrophil Cytoplasmic Antibody (MPO-ANCA) Vasculitis.

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a group of rare autoimmune diseases that affect medium and small blood vessels, with uncommon, variable central nervous system (CNS) involvement. It poses diagnosis challenges due to the limited accuracy of conventional imaging and vast differential diagnosis. We describe the case of a 76-year-old man with a previously diagnosed myeloperoxidase (MPO)-positive AAV with exclusive renal involvement. The patient presented to our emergency department (ED) with sudden-onset weakness of the right side of the body, difficulty speaking, fever, and a history of progressive cognitive impairment in the previous three months (loss of memory, time and space disorientation, acalculia). Brain imaging showed multiple acute and subacute ischemic lesions, suggesting CNS vasculitic involvement. The patient was treated with methylprednisolone pulses, followed by rituximab, with motor and cognitive improvement. Timely diagnosis and adequate treatment of AAV as a cause for new-onset neurological symptoms are crucial to improve outcomes. Otherwise, a higher risk of relapse remains, and extensive neurological deficits may become permanent. Evidence regarding the best treatment options in these patients is scarce and case reports provide further data on this topic.