What is Susac syndrome? 

Susac syndrome (SuS) is a rare, immune-mediated microvascular endotheliopathy affecting the brain, retina, and inner ear. It is characterized by the clinical triad of encephalopathy, branch retinal artery occlusions, and sensorineural hearing loss. The disease results from inflammatory injury and occlusion of small blood vessels, leading to microinfarctions and potentially irreversible tissue damage.

Clinical manifestations and diagnosis

The clinical presentation of Susac syndrome is heterogeneous and depends on the organs affected and the extent of microvascular injury.

Neurological involvement

Neurological presentation may include headache, encephalopathy, cognitive impairment, memory and concentration difficulties, behavioral or psychiatric changes, but also focal neurological deficits. Symptoms can be relatively mild to very severe and debilitating.

Ocular involvement

Retinal involvement is characterized by branch retinal artery occlusions, which may cause visual field defects, scotomas, or reduced visual acuity. Importantly, retinal vascular abnormalities may be present in patients without subjective visual symptoms.

Audiovestibular involvement

Audiovestibular involvement typically manifests as sensorineural hearing loss. Frequently the low and middle frequencies are affected. The can be accompanying tinnitus or vertigo.

Clinical triad

The diagnosis of Susac syndrome is based on characteristic clinical features and complementary investigations involving the brain, retina, and inner ear. However, the complete clinical triad is often absent or not recognized at disease onset. Consequently, Susac syndrome is frequently misdiagnosed, particularly as multiple sclerosis, central nervous system vasculitis, migraine, or other inflammatory and vascular neurological disorders [6]. Diagnostic criteria proposed by the European Susac Consortium (EuSaC) distinguish between definite and probable Susac syndrome, facilitating earlier recognition in patients with incomplete clinical presentations.

Ancillary examinations

Additional examinations are done to investigate organ involvement. 

Brain MRI

Characteristic findings include T2/FLAIR-hyperintense lesions in the corpus callosum, often described as snowball lesions. Additional features may include diffusion-restricted microinfarctions, and leptomeningeal enhancement.

Ophthalmological assessment

Retinal fluorescein angiography can reveal branch retinal artery occlusions and characteristic arteriolar wall hyperfluorescence. Optical coherence tomography may provide additional information on retinal ischemic damage and microvascular perfusion.

Audiological evaluation

Pure-tone audiometry, is essential to detect and quantify sensorineural hearing loss, including subclinical involvement.

Lumbar puncture

Cerebrospinal fluid analysis may demonstrate elevated protein concentrations. 

Treatment and prognosis

The primary objective of treatment is to rapidly suppress disease activity and prevent irreversible neurological, retinal, and cochlear damage. This generally involves immunosuppressive therapy. The second objective is to prevent future damage which is generally done with long term immunosuppressive therapy.

The disease course is variable and may be monophasic, relapsing, or chronically active. Although clinical recovery is possible, residual cognitive impairment, visual field deficits, and permanent hearing loss may persist.