Amyloid β-related Angiitis Presenting with Subarachnoid Hemorrhage Diagnosed by Brain Biopsy: A Case Report

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Cerebral amyloid angiopathy is a vascular disorder characterized by amyloid β deposition in leptomeningeal and cortical blood vessels. Rarely, amyloid β accumulation induces inflammatory responses, classified as cerebral amyloid angiopathy-related inflammation or amyloid β-related angiitis, with the latter being extremely rare. We report a case of a 74-year-old woman presenting with visual field disturbance, occipital pain, speech impairment, agraphia, and acalculia. Imaging revealed subarachnoid hemorrhage without an identifiable source on cerebral angiography. Magnetic resonance imaging demonstrated abnormal enhancement in the dura and pia mater of the left temporal and parietal lobes. Brain biopsy confirmed amyloid β-related angiitis, showing histopathological findings of amyloid deposition with granulomatous inflammation. Steroid pulse therapy led to marked clinical and radiological improvement. This case highlights the importance of considering amyloid β-related angiitis in the differential diagnosis of angiographically negative subarachnoid hemorrhage. Early recognition and immunosuppressive therapy are essential to reduce neurological deficits, with brain biopsy providing a definitive diagnosis.