General description

Susac syndrome is a rare autoimmune-mediated disorder characterized by microvascular occlusion in the brain, retina, and inner ear, leading to a clinical triad of encephalopathy, branch retinal artery occlusions (BRAO), and bilateral sensorineural hearing loss. These symptoms can occur simultaneously or in succession, with the full triad present in only 20% of patients at disease onset.

Susac syndrome predominantly affects young to middle-aged women and most cases occur in the 2nd to 4th decades of life. The syndrome is often underdiagnosed or misdiagnosed, as it is usually identified after excluding other neurological, psychiatric, ophthalmological, and auditory disorders.

Clinically, the encephalopathy seen in Susac syndrome can manifest as memory impairment, confusion, behavioral changes, ataxia, dysarthria, paranoid psychosis, and headaches. Sensorineural hearing loss typically affects low and medium frequencies, while BRAO can lead to scotomata and visual distortions, which are best identified using fluorescein angiography. Diagnosis is often delayed due to the fluctuating and sequential presentation of symptoms over a 1-2 year period.

Diagnostic criteria for Susac syndrome, proposed in 2016, require clinical and imaging evidence involving the brain, retina, and vestibulocochlear system. Brain involvement is identified by symptoms such as cognitive impairment, behavioral changes, and focal neurological deficits, alongside imaging findings like rounded T2 hyperintense "snowball lesions" in the corpus callosum, leptomeningeal enhancement, or gray matter enhancement on MRI. Retinal involvement is confirmed through ophthalmologic evaluation showing BRAO, arterial wall hyperfluorescence, or sectorial damage on optical coherence tomography. Vestibulocochlear involvement is indicated by new tinnitus, hearing loss, or vertigo, supported by audiometry and vestibular function tests. A definite diagnosis requires fulfillment of all three criteria, while a probable diagnosis can be made if two criteria are met.