Susac Syndrome - Causes, Symptoms, Diagnosis, and Treatment

Introduction

Susac syndrome is a rare autoimmune condition characterized by three main symptoms: altered brain function (encephalopathy), blockage of retinal arteries, and hearing impairment. It is named Susac syndrome after Dr. John Susac first described it in 1979. Susac syndrome occurs due to unknown causes, and the affected people show symptoms other than the main symptoms, including difficulties in speech, intense headaches, impaired vision, and hearing problems. However, some people may not exhibit classic symptoms of Susac syndrome but develop a combination of the symptoms. Susac syndrome is usually seen in women more than men.

What Is Susac Syndrome?

Susac syndrome, also known as small infarctions of cochlear, retinal, and encephalic tissues (SICRET) or retinocochleocerebral vasculopathy, is a rare autoimmune syndrome affecting more commonly young to middle-aged women. It is characterized by three main symptoms, including acute or subacute encephalopathy (brain disorder), branch retinal artery occlusion (BRAO), and bilateral hearing loss. Three forms of Susac syndrome have been observed in affected individuals based on the areas involved. In one form, the main clinical finding is encephalopathy. Branch retinal artery occlusion and hearing impairment are the main problems observed in the second form of Susac disease without any brain damage. Finally, in the third form, the patients shows encephalopathy initially and later develop hearing problems and retinal artery occlusion.

What Are the Causes of Susac Syndrome?

The exact cause of Susac syndrome is not yet known. However, it occurs due to damage to the small blood vessels (microangiopathy) present in the brain, eyes, and inner ear, resulting in hearing loss, encephalopathy, and retinal artery occlusions. Susac syndrome is considered an autoimmune condition in which the immune system cells mistakenly damage the inside lining of (endothelium) tiny blood vessel walls. These microscopic blood vessels majorly supply blood to the retina, brain, and inner ear. Damage to the endothelial cells results in swelling and blockage of blood flow through these vessels, thereby preventing oxygen and nutrients from reaching these areas.

What Are the Symptoms of Susac Syndrome?

The symptoms associated with Susac syndrome vary from person to person. It usually affects the brain, inner ear, and eyes. Therefore, affected individuals may present mainly with symptoms from these three areas. However, brain symptoms are the initial and most common ones. About 85 percent of people with Susac syndrome experience symptoms involving all three locations during the disease course.

The common symptoms involved are the following.

• Brain Symptoms.

• Confusion.

• Severe headache.

• Vomiting.

• Walking difficulties.

• Short-term memory loss.

• Reduced ability.

• Altered thinking.

• Slurred speech.

• Anxiety.

• Gait disturbances.

• Aggression.

• Depression.

• Slow thought processing.

• Psychosis.

• Behavioral changes.

• Eye Symptoms.

• Visual disturbances.

• Peripheral vision loss.

• Dark visual field.

• Ear Symptoms.

• Hearing problems.

• Vertigo.

• Tinnitus.

How Is Susac Syndrome Diagnosed?

Diagnosis of Susac syndrome is based on the presence of symptoms involving the brain, eyes, and inner ear. The process of diagnosis involves a thorough evaluation of clinical signs, detailed patient history, and specialized tests such as magnetic resonance imaging (MRI), audiogram, and fluorescein angiography.

The standard diagnostic aids used for Susac syndrome are the following.

• Magnetic Resonance Imaging (MRI) - It uses radio waves and magnetic fields to produce images of body tissues and organs. In patients with Susac syndrome, magnetic resonance imaging shows typical changes in the brain involving the corpus callosum and other areas of the brain. In addition, increased visibility of tissues that covers the brain (leptomeninges) is also seen.

• Fluorescein Angiogram (FA) - It involves tests to evaluate the blood flow in the eyes. In a fluorescein angiogram, a special dye and a camera is used to assess retinal blood flow. Individuals with Susac syndrome show abnormalities such as partial or complete occlusion of branch retinal arteries, hyper fluorescence of vessel wall, chronic changes in the periphery, leakage of dye, microaneurysms, and neovascularization.

• Audiogram - A hearing examination is carried out in individuals to rule out inner ear symptoms. An audiogram may show hearing loss and difficulty understanding speech in patients with Susac syndrome.

• Neurological examination - It is necessary to rule out neurological symptoms associated with Susac syndrome.

• Ophthalmological Examination - A complete ophthalmological examination, including visual field testing, is done to determine visual alterations associated with Susac syndrome.

What Are the Radiographic Features Observed in Susac Syndrome?

Magnetic resonance imaging (MRI) shows characteristic radiographic features. There will be small, multiple white matter lesions involving the corpus callosum. In addition to the corpus callosum, the lesions also affect other areas of the brain, such as periventricular white matter, cerebellum, middle cerebellar peduncles, and brain stem. A typical string of pearls involves the internal capsules due to punctate microinfarcts. Other findings observed in magnetic resonance imaging (MRI) are snowball or hole, or spokes-shaped lesions affecting the corpus callosum's central portion (nerves connecting the right and left halves of the brain).

What Are the Treatment Options for Susac Syndrome?

The appropriate treatment choice for Susac syndrome depends on the severity of clinical symptoms. The main treatment option used in patients with Susac syndrome is using immunosuppressive agents such as corticosteroids and intravenous immunoglobulins (IVIG) to suppress the activity of immune system cells against microvessels present in the brain, inner ear, and eyes. In patients with hearing loss, intratympanic injection of Dexamethasone can be given to improve the condition. However, cochlear implants should be used to improve hearing in cases of severe hearing loss.

Commonly used medications for managing symptoms associated with Susac syndrome are the following.

• Rituximab.

• Cyclophosphamide.

• Prednisone.

• Methotrexate.

• Azathioprine.

• Infliximab.

• Intravenous immunoglobulins (IVIG).

• Mycophenolate mofetil.

Conclusion

Susac syndrome is an autoimmune condition that affects the brain, eyes, and inner ear. Affected individuals may show hearing loss, brain diseases, and visual disturbances. The exact cause of Susac disease is not yet identified. However, various studies have concluded that it occurs when immune system cells mistakenly damage the tiny blood vessels present in the inner cell walls of the retina, brain, and inner ear. Various diagnostic aids such as magnetic resonance imaging (MRI), audiogram, fluorescein angiogram (FA), neurological examination, and ophthalmological examination can identify the symptoms associated with Susac's disease. Treatment strategies for Susac syndrome involve using immunosuppressive agents to reduce the autoimmune damage to tiny blood vessels in the brain, eyes, and inner ear.