Susac syndrome (SS) is a rare disorder that affects the brain, eyes, and inner ear. This condition is an acquired microangiopathy, involving damage to the body’s smallest blood vessels (microvessels) in specific, sensitive locations. With just over 500 cases reported worldwide, diagnosis is often significantly delayed because the full spectrum of symptoms frequently does not appear simultaneously. This makes initial recognition challenging for healthcare providers. The condition predominantly affects young to middle-aged women, typically between the ages of 20 and 40, who are affected about three times more often than men.
Defining Susac Syndrome and Its Underlying Cause
Susac syndrome is classified as a presumed autoimmune condition or an inflammatory microangiopathy. The underlying cause involves the immune system mistakenly attacking the body’s own tissues. The immune response targets the endothelial cells lining the small arteries (arterioles) in the affected organs.
This attack causes inflammation and swelling, leading to narrowing or complete blockage of blood flow (occlusion). This blockage results in small areas of tissue death, or microinfarcts, due to a lack of oxygen (ischemia). The microangiopathy is thought to be mediated by cytotoxic CD8+ T cells, which actively destroy the endothelium.
This damage is highly selective, occurring only in the arterioles of the brain, the retina, and the cochlea of the inner ear. The resulting microinfarcts are the source of symptoms and define the unique pattern of damage seen in Susac syndrome.
The Triad of Clinical Symptoms
The manifestation of Susac syndrome is characterized by the clinical triad: encephalopathy, retinal artery occlusion, and sensorineural hearing loss. Diagnosis is often complicated because only a small percentage of patients present with all three symptoms at the onset of the disease. The symptoms may appear sequentially over a period of months.
Encephalopathy, or brain involvement, is a generalized dysfunction presenting with a broad range of symptoms. Patients frequently experience severe headaches that can mimic migraines. Cognitive changes are common, including memory loss, confusion, and a reduced ability to concentrate. Behavioral changes, such as personality shifts, apathy, and sometimes psychosis, can also occur.
In the eye, the condition causes branch retinal artery occlusions (BRAOs), which are blockages in the small arteries of the retina. These blockages prevent blood flow, resulting in areas of painless vision loss called scotomas. Vision loss can sometimes be peripheral, meaning the patient may not immediately notice the defect. While severe cases can lead to significant visual impairment, many occlusions are small and temporary.
The inner ear is affected by sensorineural hearing loss caused by a lack of blood flow to the cochlea. This impairment is typically bilateral, though often asymmetric, and commonly affects the low-to-mid sound frequencies. The hearing loss can be sudden in onset and is frequently accompanied by tinnitus, a persistent ringing or roaring sound. Some patients may also experience vertigo due to microinfarcts in the semicircular canals.
Diagnostic Procedures and Differentiating Factors
Confirming a diagnosis requires objective evidence of damage across the three affected systems, as symptoms can mimic other conditions. Susac syndrome is commonly misdiagnosed, often confused with neurological disorders such as Multiple Sclerosis (MS) or acute disseminated encephalomyelitis (ADEM).
Brain magnetic resonance imaging (MRI) is a primary diagnostic tool, revealing characteristic lesions in the brain’s white matter. A distinctive finding is the presence of small, rounded lesions, sometimes called “snowball lesions,” especially within the corpus callosum. Imaging may also show enhancement in the leptomeninges, the delicate membrane covering the brain and spinal cord, suggesting an active inflammatory process.
Ophthalmological evaluation uses fluorescein angiography (FA) to visualize blood flow in the retinal vessels. This procedure involves injecting a fluorescent dye to highlight areas of blocked blood flow, confirming branch retinal artery occlusions. FA is highly sensitive for detecting both symptomatic and asymptomatic occlusions, making it essential for diagnosis and monitoring disease activity.
For the inner ear, audiometry is performed to confirm the pattern of sensorineural hearing loss. The classic pattern involves hearing loss in the low-to-mid frequencies, which is a specific marker for cochlear damage. Establishing a definite diagnosis requires the combination of specific MRI findings, confirmed retinal occlusions on FA, and the characteristic audiogram pattern.
Current Treatment Strategies and Long-Term Outlook
Treatment focuses on rapidly suppressing the immune system’s attack to prevent further damage. Since the condition is rare, there are no randomized controlled trials, so treatment protocols are based on clinical experience.
Acute treatment typically begins with high-dose intravenous corticosteroids, such as methylprednisolone, to quickly reduce inflammation. Immunosuppressive therapies are often added to achieve sustained remission and prevent relapse. These aggressive therapies may include intravenous immunoglobulin (IVIg) or cyclophosphamide, a strong immunosuppressant.
Following the acute phase, patients transition to maintenance therapy to prevent disease recurrence, which can last two years or longer. This management often involves lower doses of oral corticosteroids combined with other immunosuppressive agents like mycophenolate mofetil or azathioprine. The treatment response is closely monitored through regular clinical evaluations, follow-up brain MRIs, and fluorescein angiography.
The long-term outlook varies among individuals. The disease course is often monophasic, meaning it runs its course and then becomes inactive, usually within one to three years. However, some patients experience a polycyclic course with relapses, or a chronic-continuous course. While the encephalopathy and visual symptoms often improve or resolve with treatment, hearing loss is frequently permanent due to the delicate nature of the cochlear structures. Early and aggressive treatment is linked to a better outcome, and many patients are able to return to their normal lives, though some may experience lasting cognitive or auditory deficits.