Susac\'s syndrome

Clinical History

A 39-year-old male patient presented with bilateral hearing loss, visual distortion, inappropriate behaviour, dysarthria and headaches. Serology for infectious disease, tumoral and onconeuronal markers were negative. CSF showed elevation of proteins 162 g/dl (15-45 g/dl) and IgG 16.5mg/dl (1.0-4.0).
Electroencephalography revealed no epileptiform activity.

Imaging Findings

Brain MRI evidenced multifocal hyperintense foci on T2 weighted images and T2-FLAIR localized mainly in the central part of the corpus callosum, with lesions seen in the genu, corpus, and splenium resembling a “punched-out” appearance (Fig. 1a-b, Fig. 2) There was also multiple small hyperintense focus on the periventricular white matter (Fig. 1b) and on the right internal capsule with a "string of pearl" pattern (Fig. 1c). Diffusion-weighted images and apparent diffusion coefficient map showed mild restriction on corpus callosum knee and splenium (Fig. 3).
Retinal fluorescein angiogram showed peripheral arteriolar obstruction and hyperfluorescent arterial walls (Fig. 4).

Discussion

Susac's syndrome (SS), also known as SICRET (small infarctions of cochlear, retinal, and encephalic tissue) RED-M (microangiopathy with retinopathy, encephalopathy and deafness) or retinocochleocerebral vasculopathy [1]. Is an uncommon neurology disorder with near 200 cases reported in literature [2]. SS aetiology and pathogenesis is unknown but it is believed to be an immune-mediated endotheliopathy that affects the microvasculature of the brain, retina and inner ear [3]. Other theories are vasospastic phenomena, coagulopathy or viral infection.

Susac's syndrome presents with a clinical triad of encephalopathy, retinal artery branch occlusion and bilateral hearing loss [1]. It’s a subacute progressive process and only 13% of patients present the complete triad on the first consult [4], the imaging findings being a key for the diagnosis. Electroencephalogram and audiometry can demonstrate absence of epileptiform activity and sensorineural hearing loss [5]. Retinal fluorescein angiogram demonstrates branch retinal artery occlusion, retinal infarcts and arterial wall hyperfluorescence secondary to fluorescein leakage in a damaged vessel; these findings will establish or confirm the diagnosis in many cases [6].

MRI is the best imaging technique for the diagnosis, T2 and T2-FLAIR hyperintense lesions on the central fibres of the corpus callosum with a "punched out" appearance is the most typical finding described in 100% of patients with SS. Periventricular, cortical, deep white matter and grey matter may also be involved. When multiple lesions are seen on the internal capsule, referred as "string of pearl" configuration, combined with the central corpus callosum lesions are consider pathognomonic for SS [7]. Parenchymal lesions or leptomeninges can enhance after intravenous contrast administration, and may show restricted diffusion [1].

Susac's syndrome must be differentiated from multiple sclerosis, although in both cases we find white matter involvement, multiple sclerosis usually affects corpus callosum septal interface, not the central fibres as on Susac´s syndrome and does not involved the grey matter. [1, 5]

Susac's syndrome requires aggressive treatment with immune suppressive therapy with glucocorticoids, immunoglobulin and cyclophosphamide, azathioprine, mycophenolate-mofetil and plasmapheresis; antithrombotic agents to prevent thrombi formation and infarction. Early treatment improves residual symptoms and could have an effect on the clinical course of the disease. [3]

Prognosis varies depending on immunomodulation response, with recurrent-remittent course, while others could relapse for a long time (decades). [2]

The clinical triad recognition (encephalopathy, hearing loss and visual disturbances) and compatible radiological imaging (corpus callosum lesions) are fundamental in early diagnosis before initiating immunosuppression treatment, as well as for neuroimaging follow-up in order to detect clinical changes indicating recurrence of the disease.

Differential Diagnosis List

Final Diagnosis

Susac's syndrome

URL:	https://www.eurorad.org/case/12253
DOI:	10.1594/EURORAD/CASE.12253
ISSN:	1563-4086