Phenotypic and Etiological Characterization of Susac Syndrome

Susac's Syndrome (SS) is characterized by the clinical triad of encephalopathy, hearing loss, and retinal artery branch occlusions. Since the first description of SS in 1979, hundreds of patients with SS, mostly young women, have been reported. However, comprehensive epidemiological, clinical and etiological features of SS have never been specifically addressed so far.

The diagnosis of SS is difficult because its characteristic signs often do not occur simultaneously or may be too subtle for the patient to notice. Neurological features of SS may occur several months prior to other symptoms. The retinal artery branch occlusion, by occurring in the peripheral portion of the retina, may remain asymptomatic. Sensorineural hearing loss may also be asymptomatic and disclosed only by audiogram. Besides mild pleocytosis in cerebro-spinal fluid, all performed biological tests are virtually negative. No infectious agent, consistent autoimmune marker, or coagulopathy has been disclosed. Changes seen on brain MRI are well characterized although not specific. The only site from which biopsy material is available for pathological analysis is the brain. The most common finding in brain biopsies is the presence of microinfarcts but brain biopsy is not currently performed.

Although the treatment of SS has not been studied in controlled trials, most patients have a good response to treatment with glucocorticoids, with the addition of antithrobomtic therapy and, for cases in which the disease is refractory to steroids, intravenous immune globulin or cyclophosphamide. The clinical course is characterized by recurrent attacks involving 1 or more components of the triad that characterize the active phase of the disease. Remission usually occurs after the active phase but some patients show residual mild to moderate dementia or gait disturbance, and impaired hearing and vision.

Susac's Syndrome is a vasculopathy causing small infarcts in the cochlea, retina and brain. Proposed explanations include a hypercoagulable state, vasospasm, and vasculitis, none of which are supported by laboratory results or findings on brain biopsies. The unique distribution of arteriolar disease affecting the brain, the retina, and the cochlea suggests selective vulnerability of these three structures. The brain, retina, and cochlea all have a blood-tissue barrier, and the endothelium in these sites shares a common embryologic origin and unique structural and antigenic characteristics. It has therefore been proposed that SS is an autoimmune disease in which the endothelium is the primary target, and damage to the endothelium triggers arteriolar occlusion and microinfarcts. However, the pathogenesis remains unknown.

The objective of this study is to characterize the epidemiological, clinical, and etiological features of Susac's Syndrome. In this aim, we will constitute a national clinical-based cohort including all SS new cases prospectively observed. French Society of Neurology, Ophtalmology and Internal Medicine will be asked to collaborate.The exhaustive and systematic analysis of each case will help to better define different aspects of the disease such as the incidence and prevalence, the clinical presentation, the diagnostic modalities and the impact of treatments.