Susac syndrome (SS) is a rare disorder characterized by the triad of central nervous system (CNS) dysfunction, branch retinal artery occlusions (BRAOs) and sensorineural hearing loss (SNHL). It is presumably due to autoimmune-mediated occlusions of microvessels in the CNS, the retina, and the inner ear.
The prevalence of SS is still unknown but to date more than 300 cases have been reported worldwide. Young females (20-40 years) are more affected (ratio 3.5:1).
The age of onset ranges from 8 to 72 years (mean age 32 years). Clinically, SS consists of the triad of encephalopathy and/or focal CNS dysfunction, BRAOs and SNHL. However, all tree components are rarely present at initial presentation. SS is often preceded by headache (migrainous or constant). Encephalopathy is characterized by memory loss, confusion, disorientation, behavioral disturbances, personality changes and psychosis. Focal CNS signs include ataxia, motor and sensory impairment, dysarthria and oculomotor dysfunction. Optic involvement includes scotoma and visual distortion. BRAOs may also occur at the periphery and not result in clinical deficits. Hearing loss, usually in the low to mid frequencies, may be associated with roaring tinnitus and vertigo. Myalgia and/or arthralgia and urinary dysfunction may occasionally be observed. According to the clinical course, classification into three major forms has been suggested: monocyclic (fluctuating disease that self-limits after a maximum period of 2 years and does not recur), polycyclic (relapses that continue beyond a 2 year period) and chronic-continuous.
The etiology is unknown, although it is thought to be an autoimmune process leading to inflammation and occlusion of the pre-capillary arterioles of the brain, retina, and inner ear.
Diagnosis of SS includes magnetic resonance imaging studies (MRI) that show characteristic ''punched out'' lesions of the central fibers of the corpus callosum (''snowball lesions''). Periventricular lesions and involvement of the cerebellum, brain stem and deep grey matter nuclei are often present. Retinal fluorescein angiography findings demonstrate BRAO and fluorescein leakage. Audiometry analysis reveals uni- or bilateral SNHL. Cerebrospinal fluid analysis often shows mild pleocytosis and moderate protein elevation, while oligoclonal bands are uncommon. The impact of autoantibody diagnostics is currently under investigation.
Differential diagnosis includes inflammatory demyelinating CNS disease (such as multiple sclerosis, acute disseminated encephalitis, neuromyelitis optica (Devic's disease); see these terms), other diseases involving the CNS (Meniere disease (see this term), infections, malignancies, psychotic disorders, cerebrovascular disease and isolated branch retinal artery occlusion) and autoimmune diseases (limbic encephalitis, Cogan syndrome, Eales disease, autoimmune inner-ear disease, polyarteritis nodosa, Wegener granulomatosis, Churg-Strauss syndrome, systemic lupus erythematosus, antiphospholipid syndrome, Sjögren syndrome and Behçet disease; see these terms).
No evidence-based treatment strategies exist. Empiric treatment includes aggressive multimodal immunosuppressive therapy in the acute period, with high doses of corticosteroids, cyclophosphamide, methotrexate, azathioprine and/or mycophenolate mofetil, and intravenous immunoglobulins. After the acute period, treatment is continued with a slow tapering of corticosteroids. Alternative drugs, such as rituximab, etanercept or cyclosporine A, may be helpful in refractory cases. Patients with severe hearing loss may benefit from cochlear implants. Platelet aggregation inhibition is advised empirically.
The disease is usually self-limiting, often stabilizing in 2-4 years, but often results in various cognitive, visual and/or hearing deficits. Late relapses and chronic progressive courses may occur.
Last update: September 2013