Susac syndrome: a neuropathological description of an underdiagnosed entity

Abstract

Susac syndrome is an under-recognised disease characterised by the clinical triad of encephalopathy, retinal artery occlusion and sensorineural hearing loss. It is thought to be due to a microangio-pathy of uncertain aetiology. Only limited histopathological descriptions are available. We aimed to better characterise the neuropathological features of Susac syndrome and to define the vascular pathology present. Neurosurgical biopsies from three cases of Susac syndrome were examined morphologically, histo-chemically and immunohistochemically. Controls included cerebral and cerebellar tissue from six age matched cases. In addition, patient serum was assessed in a direct immunofluores-cence assay. All three cases had cortical microinfarcts of varying ages. Acute cases showed perivascular CD8 positive lymphocytic cuffs with endothelial swelling and subtle micro-infarcts. Older cases showed thick walled, non-congophilic, hyalinised blood vessels. Intravascular fibrin thrombi, disrupted elastic lamina or complement activation was not seen. Serology testing revealed IgG binding to the internal elastic lamina in one case, a non-specific finding. We conclude that the neuropathology of Susac syndrome is relatively non-specific, and that vascular damage is T-cell-mediated rather than due to humoral responses. Awareness of the clinical, radiological and neuropathological features will aid the pathologist in alerting clinicians to the possibility of this treatable disorder.