Susac Syndrome: A differential diagnosis of white matter lesions

Susac Syndrome is an autoimmune endotheliopathy affecting capillaries and precapillary arterioles of the brain, inner ear and retina. The classic symptom triad includes visual disturbances, hypoacusia, and encephalopathy, but is rarely fully manifest at onset. The syndrome typically follows an active fluctuating monophasic course. Typical imaging findings on brain magnetic resonance show central fiber microischemias/microinfarctions of the corpus callosum known as "snow balls", as well as lineal infarcts and upper callosal fiber involvement. Fluorescein angiography and tonal audiometry are important tools to confirm diagnosis, even in patients who are asymptomatic for visual or auditory disturbances. We describe 8 patients with Susac Syndrome treated at our center and compare findings to those of other published case series.

Eight adults with Susac Syndrome diagnosed between January 2007 and August 2016 at our center, in Buenos Aires, Argentina are described. Magnetic Brain Resonance, fluorescein angiography, tonal audiometry, a complete serologic battery and lumbar puncture were performed to all patients.

The majority of patients were males, and average age at diagnosis was 37.5 years (range: 22-52 yrs). Two patients presented full clinical triad at onset, while the remaining developed visual and/or auditory disturbances later during the course of disease. All cases manifested varied neurological symptoms including pyramidal and/or sensory tract symptoms, amnesic disorders, ataxia and vertigo. Psychiatric manifestations such as disinhibition, aggressive behavior, paranoid ideation and hallucinations were also present. Seven patients suffered at least one relapse. Typical central corpus callosum fiber ischemias/infarcts, also known as snowball lesions were visible in all patients. Spokes, icicles, periventricular lesions and internal capsule "string of beads" patterns were observed on diffusion weighted images. Four cases presented fornix microischemias/microinfarctions, 5 juxtacortical involvement and 3 infratentorial infarcts. Leptomeningeal involvement was evident in only 1 patient after rabies vaccination. Fluorescein angiography was abnormal in 7 cases. Tonal audiometry revealed unilateral hypoacusia in 5 patients, 3 with low frequency hearing loss. Immunosuppressive treatment was indicated in all cases. Patient follow up ranged between 6 months and 9 years, only 1 patient was lost to follow up after three years.

Susac Syndrome is probably both underdiagnosed and misdiagnosed. Early and aggressive immunosuppressive treatment is indicated in order to prevent potential disabilities.