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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 enhancement

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

  • No standardized treatment protocol
  • Immunosuppressive therapy:
    • High-dose corticosteroids (e.g., methylprednisolone)
    • Cyclophosphamide or methotrexate in refractory cases
  • Supportive care:
    • Antiepileptic drugs for seizure control
    • Cognitive rehabilitation
  • Monitoring:
    • Regular clinical and radiological follow-up
    • Assess for recurrence and treatment response

Differential diagnosis

Differential Diagnosis Differentiating Feature
Multiple Sclerosis Ovoid periventricular and callosal lesions; Dawson's fingers on sagittal FLAIR; no cortical microbleeds or siderosis
Acute Disseminated Encephalomyelitis (ADEM) Diffuse bilateral white matter T2 signal with basal ganglia involvement; no microbleeds or siderosis
Primary CNS Vasculitis Multifocal cortical and subcortical infarcts; vessel wall enhancement on high-resolution MRI; no cortical microbleeds
Posterior Reversible Encephalopathy Syndrome (PRES) Posterior-predominant vasogenic oedema with elevated ADC; no microbleeds; resolves on follow-up
Gliomatosis cerebri / High-grade glioma Infiltrating T2 signal abnormality with mass effect; enhancement in high-grade tumours; no lobar microbleeds
Cerebral Abscess Thin smooth ring-enhancing lesion with restricted DWI; surrounding vasogenic oedema; no siderosis
Progressive Multifocal Leukoencephalopathy (PML) Subcortical U-fibre involvement; no enhancement or mass effect; restricted diffusion at active edge; no microbleeds
Acute Ischaemic Stroke Wedge-shaped DWI restriction following vascular territory; no microbleeds or leptomeningeal enhancement
Cerebral Venous Thrombosis Filling defects in venous sinuses on CT/MR venography; venous infarcts crossing arterial territories
Creutzfeldt-Jakob Disease Cortical ribboning and basal ganglia DWI restriction; pulvinar sign on T2; no microbleeds