Susac syndrome: brain, eye and hearing symptoms, diagnosis and treatment

NORD, the US National Organization for Rare Disorders, describes Susac syndrome as a relatively rare disorder characterised by three main problems: impaired brain function, partial or complete blockage of the small arteries supplying the retina, and inner ear disease. It is an autoimmune disease in which the person's own immune system mistakenly attacks the lining of the smallest blood vessels (the capillaries, venules and arterioles) in the brain, retina and inner ear. The cells swell and the tiny vessels become blocked, reducing the supply of oxygen and nutrients to those three organs.

The exact reason why this happens is unknown. It was first described in the medical literature in 1979 by Dr John Susac, and it is also referred to as RED-M or SICRET. The syndrome is thought to be underdiagnosed, partly because it is easily mistaken for other conditions.

The specific symptoms, severity and outcome vary from person to person. NORD says that the three main features are commonly not all present at onset, and that headaches, including migraine-like headaches, often come before other symptoms.

• Brain: confusion, memory loss, decreased executive function, gait disturbance, slurred speech, and sometimes paranoia or personality and behavioural changes.

• Eyes: a dark spot or black area in the field of vision, or a sensation of a curtain or shade being drawn across part of the vision, due to branch retinal artery occlusion. One or both eyes may be affected and permanent vision impairment can occur.

• Ears: hearing loss, which NORD says is primarily at low frequencies and usually fairly sudden, often with intense ringing (tinnitus) and sometimes vertigo.

• Skin: in some people a net-like mottling (livedo reticularis) or a rash.

NORD says the encephalopathic form is frequently misdiagnosed as multiple sclerosis or acute disseminated encephalomyelitis, and that when it presents with hearing loss, tinnitus and vertigo it may be mistaken for Meniere disease. A published review notes that improvement of the encephalopathy after a short course of steroids can reinforce a wrong diagnosis, and that the correct diagnosis may only emerge when the illness returns as steroids are tapered and other features appear.

A second reason is that retinal blockages may not be noticed. NORD notes that patients often continue to have 20/20 vision even after branch retinal artery occlusions, and the review says peripheral involvement can cause no symptom, which is why a specialist eye examination is so important.

NORD says a diagnosis of definite or probable Susac syndrome is based on at least two components of the triad together with typical "snowball" lesions in the corpus callosum on brain MRI. A detailed history, a review of all other plausible explanations, and specialised tests are needed, including MRI, fluorescein angiography and an audiogram. A complete neurological and ophthalmological examination is essential.

The review explains that there is no single specific test and the diagnosis is made from the characteristic clinical triad and the exclusion of other conditions. NORD recommends a fluorescein angiogram, an eye test that uses a dye and a camera to look at blood flow in the retina, even in people with no eye symptoms, and an audiogram for all patients with suspected Susac syndrome even if they have not noticed hearing symptoms. Dilated examination of the retina may show small yellow Gass plaques in the retinal arterioles.

NORD says that although Susac syndrome can sometimes subside spontaneously, early, appropriately aggressive and sustained treatment is needed while it is active. The two mainstays are immune-suppressing medicines, corticosteroids such as prednisone and intravenous immunoglobulin, with other drugs added when needed, including mycophenolate mofetil, azathioprine, cyclophosphamide, rituximab and anti-TNF treatments. The choice depends on severity.

Hearing support is part of care. NORD says a hearing aid may be indicated for significant hearing loss and cochlear implantation may be beneficial for profound loss. It says the encephalopathic form often resolves within 1 to 3 years, while the other forms tend to follow a more prolonged, chronic or recurrent course for 3 to 10 years or more, and that all forms need immunosuppressive treatment while active. Relapse after a long remission is rare but can occur.

No dedicated NHS information page for Susac syndrome was found, and the sources used for this guide are international, so the details below are general. Because the condition spans the brain, eyes and ears, care typically involves neurology, ophthalmology and audiology working together, often at a specialist centre, with rheumatology or immunology input for treatment. Anyone with unexplained confusion, patchy vision loss or sudden hearing loss should seek prompt medical assessment, and sudden hearing loss in particular needs urgent attention.

If you have been diagnosed with multiple sclerosis but your course seems unusual, particularly if hearing loss or retinal problems appear, it is reasonable to ask your specialist whether Susac syndrome has been considered.