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Susac Syndrome

Summary

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  • Rare autoimmune microangiopathy affecting the brain, retina, and inner ear
  • Characterised by encephalopathy, branch retinal artery occlusions, and hearing loss
  • Diagnosis relies on clinical triad and characteristic MRI findings

Pathophysiology

  • Autoimmune-mediated endotheliopathy affecting small arteries
  • Microinfarcts in the corpus callosum, retina, and cochlea
  • Exact aetiology unknown, but likely involves anti-endothelial cell antibodies

Demographics

  • Predominantly affects young women (20-40 years old)
  • Male to female ratio approximately 1:3
  • Rare condition with an estimated incidence of 0.14 per 100,000 person-years

Diagnosis

  • Clinical triad:
    • Encephalopathy
    • Branch retinal artery occlusions
    • Sensorineural hearing loss
  • Often presents with incomplete triad initially
  • Diagnostic criteria:
    • At least two of the three clinical manifestations
    • Characteristic MRI findings
    • Exclusion of other differential diagnoses

Imaging

  • MRI brain:
    • Characteristic 'snowball' lesions in the corpus callosum
    • Multiple small (3-7 mm) T2/FLAIR hyperintense lesions
    • Lesions involve central fibres of corpus callosum, sparing the periphery
    • Leptomeningeal enhancement may be present
  • Fluorescein angiography:
    • Branch retinal artery occlusions
    • Arterial wall hyperfluorescence
  • Optical coherence tomography:
    • Retinal thinning in areas of infarction

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  • A 30-year-old patient presented with a sensorineural hearing loss.
  • MRI showed hyperintensities, some of which enhanced, within cerebral white matter with particular involvement of the corpus callosum.

Treatment

  • Early diagnosis and aggressive immunosuppression crucial
  • First-line therapy:
    • High-dose intravenous methylprednisolone followed by oral prednisolone
    • Intravenous immunoglobulin (IVIG)
  • Second-line therapy:
    • Cyclophosphamide
    • Rituximab
    • Mycophenolate mofetil
  • Maintenance therapy:
    • Low-dose prednisolone
    • Mycophenolate mofetil or azathioprine
  • Symptomatic management:
    • Antiepileptic drugs for seizures
    • Hearing aids for hearing loss
    • Aspirin for antithrombotic effect

Differential diagnosis

Differential diagnosis Differentiating feature
Multiple sclerosis Calloso-septal interface lesions (Dawson fingers) at the undersurface of the corpus callosum rather than central fibres; periventricular and juxtacortical ovoid plaques; no cortical microinfarcts
Acute disseminated encephalomyelitis Large bilateral confluent T2 lesions involving grey and white matter; posterior fossa and basal ganglia involvement; no central corpus callosum "snowball" lesions
CNS vasculitis Cortical and subcortical microinfarcts in multiple vascular territories; vessel wall enhancement on high-resolution MRI; no central corpus callosum predilection
Lyme neuroborreliosis Periventricular and subcortical white matter T2/FLAIR lesions similar to MS; cranial nerve and meningeal enhancement; no central corpus callosum snowball pattern