Diagnostic Criteria of Susac Syndrome
Susac syndrome is classically diagnosed with either:
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A clinical triad that consists of
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Retinal artery occlusion​
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Sensorineural hearing loss
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Encephalopathy
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A radiologic triad that consists of:
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White matter lesions​
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Deep gray matter lesions
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Leptomeningeal disease
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However, some patients will present with an incomplete clinical or radiologic triad which makes the diagnosis difficult. In a “state of art review” published in the March 2019 edition of the JNO, (click on logo for full text) Robert A.Egan suggests two other findings that are pathognomonic of Susac Syndrome and can help in making a diagnosis in these challenging situations
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Arterial wall hyperfluorescence (AWH) remote from retinal ischemia
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Central callosal lesions on MRI
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Here is an summary of what these two other findings consist of. Click on the full article link at the bottom of the page to have access to the full article, which also provides an overview of the treatment options for SS.
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ARTERIAL WALL HYPERFLUORESCENCE:
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Fluorescein Angiography is very useful in diagnosing and following patients with SS. Arterial wall hyperfluorescence which presents as staining of arterioles on FA and reflects vessel wall damage is usually seen at sites of retinal infarction in SS. However, when seen in NORMAL APPEARING RETINAL ARTERIOLES (outside sites of infarction), this finding is PATHOGNOMONIC of SS.
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CENTRAL CALLOSAL LESIONS:
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It is know from the literature that the corpus callosum is involved in all cases of SS. They are described as "snowball" or "spoke" and eventually cavitate and look like holes. They are thought to be the result of infarction of small arterioles in the central part of the corpus callosum.
The central callosal lesions are PATHOGNOMONIC of SS and tend to be present in mildly affected patients as opposed to leptomeningeal enhancement which is usually seen in more fulminant disease. Therefore, being familiar with the appearance of central callosal lesions on MRI can help in making an earlier diagnosis of SS.
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Link to full article: https://journals.lww.com/jneuro-ophthalmology/Fulltext/2019/03000/Diagnostic_Criteria_and_Treatment_Algorithm_for.13.aspx
