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Susac Syndrome

Summary

fleuron

  • 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 findings1

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

panels-1

  • 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

  • Immunosuppression (corticosteroids, IVIG, ± rituximab). The central corpus callosum "snowball" lesions (sparing the periphery, unlike MS) are the imaging signature

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

  1. Marrodan et al. Susac syndrome: challenges in the diagnosis and treatment. 2022. Brain : a journal of neurology - Open in new tab. ↩