Features
Susac syndrome is an immune-mediated disease of the brain, retina, and inner ear that produces ischemia, pauci-inflammation, and occlusive microvascular endotheliopathy.
The three common manifestations of Susac syndrome are encephalopathy, branch retinal artery occlusion (BRAO), and low-to-medium frequency sensorineural hearing loss. The classic finding seen on MRI includes supratentorial “snowball” lesions in the central corpus callosum. Susac syndrome often affects more women than men (3:1 ratio) with age ranging between 20 and 40 years. Less than 20% of all patients present with all the aforementioned triad of clinical symptoms. Initially, only one of the symptoms may present with the other components presenting weeks or up to months later. This, in turn, can delay the diagnosis and subsequent treatment of the disease.
74.1.1 Symptoms
Possible loss of peripheral vision and/or central scotomas is often described. Review of systems can reveal signs of auditory involvement including tinnitus and hearing loss. Neurologic symptoms indicative of encephalopathy includes mood changes, headaches, emotional lability, and motor and sensory loss.
74.1.2 Exam Findings
Ophthalmic findings in Susac syndrome are consequences of acute BRAOs or evidence of previous occlusion(s). In the acute setting, branch retinal artery thinning, cotton wool spots, and retinal whitening are seen on clinical exam. In those presenting with previous BRAO, sclerotic and thinned vessels may be seen. Additional evidence of retinal capillary remodeling (telangiectasias and microaneurysms) can also be observed.
74.2 Key Diagnostic Tests and Findings
74.2.1 Optical Coherence Tomography
Thinning of the inner retina in areas of previous BRAOs will be found (▶ Fig. 74.1). In an acute BRAO, inner retinal hyperreflectance is seen. More mild areas of ischemia may demonstrate middle retinal hyperreflectances (e.g., PAMM-like lesions).
Fig. 74.1 Optical coherence tomography B-scan demonstrating focal inner retinal atrophy consistent with previous branch retinal artery occlusion.
74.2.2 Fluorescein Angiography or Ultra-Widefield Fluorescein Angiography
Ultra-widefield fluorescein angiography (UWFA) is a key diagnostic for Susac syndrome. Loss of retinal artery perfusion and associated capillary nonperfusion consistent with BRAO can be seen in one or both eyes. Often, evidence of previous BRAOs can be seen as evidenced by multifocal peripheral capillary nonperfusion and/or posterior capillary remodeling. In the acute setting, segmental retinal vessel wall hyperfluorescence can be seen (▶ Fig. 74.2).
Fig. 74.2 Ultra-widefield fluorescein angiography demonstrating segmental vascular leakage and multifocal areas of nonperfusion.
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