A Rare Case of Cerebral Amyloid Angiopathy-Related Inflammation With Subarachnoid Diffusion Restriction Mimicking Rheumatoid Meningitis

Some patients with cerebral amyloid angiopathy (CAA), which is characterized by amyloid β fibril deposition in cortical and leptomeningeal vessels, develop an inflammatory response, leading to CAA-related inflammation (CAA-RI). In such cases, histopathologically confirmed vasculitis is defined as amyloid β-related angiitis (ABRA). Here, we report the rare case of an 80-year-old woman who presented with anomic aphasia and mild right upper limb weakness. Magnetic resonance imaging revealed restricted diffusion in the subarachnoid space along the cerebral sulci and dura mater, mainly within the left parietal lobe. Additional imaging findings included lobar microbleeds, edematous white matter changes, and leptomeningeal and dural enhancement. Brain biopsy revealed vasculitis with amyloid β deposition, consistent with ABRA. Marked lymphoplasmacytic infiltration, which was present in the leptomeninges and the dural surface, was considered the cause of the subarachnoid diffusion restriction. Immunosuppressive treatment led to clinical and radiological improvement. As illustrated in this case, CAA-RI may present with atypical findings of subarachnoid diffusion restriction and dural involvement, and the recognition of these features, which can mimic rheumatoid meningitis and other inflammatory conditions, is important for differential diagnosis.