Cerebral Amyloid Angiopathy-Related Inflammation Mimicking Posterior Reversible Encephalopathy Syndrome: A Case Report of Subacute Gerstmann Syndrome in an Elderly Patient.

Cerebral amyloid angiopathy-related inflammation (CAA-RI) is a rare immune-mediated complication of cerebral amyloid angiopathy in elderly patients and may closely mimic posterior reversible encephalopathy syndrome (PRES) both clinically and radiologically, making diagnosis challenging. Even though there is an apparently favorable initial outcome after steroid or immunosuppressive treatment, the CAA-RI course is unpredictable and may be associated with relapse or unfavorable neurological outcomes. We report a 76-year-old woman who presented with alexia, acalculia, mild right hemiparesis, and diplopia, consistent with a partially expressed Gerstmann syndrome. Cerebrospinal fluid analysis showed elevated protein without pleocytosis, while the electroencephalography (EEG) demonstrated focal slowing. Serological testing revealed antinuclear antibody (ANA) positivity and Borrelia burgdorferi IgG seropositivity in serum without evidence of intrathecal antibody synthesis. After exclusion of infectious, ischemic, and vasculitic etiologies, the diagnosis of probable CAA-RI was established according to the Boston criteria version 2.0, based on the clinical presentation and characteristic MRI findings, including white matter hyperintensities in a multispot pattern. High-dose intravenous corticosteroid therapy was initiated, resulting in marked clinical improvement. The diagnosis of CAA-RI was supported by the overall patient presentation, characteristic imaging findings, exclusion of alternative etiologies, and response to immunosuppressive treatment. This case highlights the diagnostic challenge of distinguishing CAA-RI from PRES and emphasizes the importance of early recognition to enable timely treatment.