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Cerebral Amyloid Angiopathy-Related Inflammation (CAA-ri)

Summary

  • CAA-ri is a rare inflammatory variant of cerebral amyloid angiopathy
  • Characterised by acute to subacute onset of headache, cognitive decline, seizures, and focal neurological deficits
  • MRI typically shows asymmetric white matter hyperintensities, microbleeds, and leptomeningeal enhancement1

Pathophysiology

  • Inflammatory response to β-amyloid deposits in cerebral vessel walls
  • Two proposed mechanisms:
    1. Autoimmune response against amyloid-β
    2. Excessive clearance of amyloid-β by activated microglia
  • Associated with APOE ε4/ε4 genotype

Demographics

  • Rare condition, exact prevalence unknown
  • Typically affects older adults (mean age 67 years)
  • No clear gender predilection

Diagnosis

  • Clinical presentation:
    • Acute to subacute onset of symptoms
    • Headache, cognitive decline, seizures, focal neurological deficits
  • Diagnostic criteria (all required) :
    1. Acute/subacute onset of symptoms
    2. Age ≥40 years
    3. ≥1 of: headache, decreased consciousness, behavioural change, focal neurological signs
    4. MRI findings consistent with CAA-ri
    5. Absence of neoplastic, infectious, or other cause

Imaging

  • MRI findings:
    • Asymmetric white matter hyperintensities on T2/FLAIR
    • Microbleeds on susceptibility-weighted imaging (SWI)
    • Cortical superficial siderosis
    • Leptomeningeal enhancement
    • Lobar microbleeds or lobar haemorrhages
  • CT findings:
    • Hypodensities in affected white matter
    • May show lobar haemorrhages

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Treatment

  • Immunosuppression (high-dose corticosteroids, occasionally cyclophosphamide) usually produces clinical and radiological improvement, supporting the diagnosis

Differential diagnosis

The key is the background of lobar microbleeds and cortical superficial siderosis; without it, consider:

Imaging differential Differentiating feature
PRES Posterior-predominant vasogenic oedema, symmetric, resolves on follow-up, without lobar microbleeds/siderosis
Primary CNS vasculitis Multifocal infarcts and vessel wall enhancement rather than confluent asymmetric white matter oedema
Infiltrating glioma Expansile T2 signal with mass effect, no siderosis
Progressive multifocal leukoencephalopathy Subcortical U-fibre disease with a restricting active edge, no enhancement or microbleeds

  1. Laterza et al. Cerebral amyloid angiopathy-related inflammation (CAA-ri): an updated systematic review and meta-analysis. 2026. Journal of neurology - Open in new tab. ↩