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ARTICLES: J. O. Susac, F. R. Murtagh, R. A. Egan, J. R. Berger, R. Bakshi, N. Lincoff, A. D. Gean, S. L. Galetta, R. J. Fox, F. E. Costello, A. G. Lee, J. Clark, R. B. Layzer, and R. B. Daroff MRI findings in Susac’s syndrome Neurology 2003; 61: 1783-1787 [Abstract] [Full text] [PDF]

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Reply to Lim et al

John Susac, R. Bakshi, A.D. Gean, F.R. Murtagh, R.B. Daroff   (5 February 2004)

MRI findings in Susac’s syndrome

CC Tchoyoson Lim, Chai Beng Tan, T Umapathi   (5 February 2004)

Reply to Lim et al 5 February 2004
John Susac 50 Second Street, SE, Winter Haven, FL 33880, R. Bakshi, A.D. Gean, F.R. Murtagh, R.B. Daroff Send Correspondence to journal: Re: Reply to Lim et al jsusac{at}neurohaven.com John Susac, et al.	We thank Dr. Lim et al for their interest in our paper, and congratulate them for making the correct diagnosis of Susac's syndrome, which is frequently missed at major academic medical centers in the United States. We have seen positive diffusion-weighted MRI images (DWI's) in Susac's syndrome, but do not feel that they reliably differentiate the syndrome from demyelinating diseases, which may also show hyperintensity on DWI. [5] Ideally, the information derived from DWI should be correlated with apparent diffusion coefficient (ADC) maps to differentiate a true restricted diffusion abnormality from T2 shine-through. Bright lesions on DWI that are associated with decreased ADC probably only indicate that the lesions, of whatever etiology, are "active". Numerous disease processes besides ischemia may demonstrate restricted diffusion on DWI scans (infection, neoplasm, trauma, demyelination, etc.). Even the presence of true restricted diffusion does not differentiate among various causes of ischemia, such as vasculitis, thrombosis, and emboli. Moreover, the restricted diffusion abnormality in ischemia is a transient finding, often lasting for about four weeks, and might readily be missed at various stages of Susac's syndrome. References 5. Zivadinov R, Bakshi R. Role of MRI in multiple sclerosis I: inflammation and lesions. Frontiers in Bioscience 2004;9:665-683.
MRI findings in Susac’s syndrome 5 February 2004
CC Tchoyoson Lim, National Neuroscience Institute, Department of Neuroradiology 11 Jalan Tan Tock Seng, Singapore 308433, Chai Beng Tan, T Umapathi Send Correspondence to journal: Re: MRI findings in Susac’s syndrome Tchoyoson_Lim{at}ttsh.com.sg CC Tchoyoson Lim, et al.	We read with interest the article by Susac et al, [1] describing the MRI findings in Susac Syndrome (SS). Recently, we saw a 26-year-old man whose MRI findings were typical of SS (Figure 1), and in whom the diagnosis of demyelinating disease was considered. However, on diffusion-weighted MRI (DWI), the lesions were hyperintense (Figure 2), and this prompted a successful clinical review for the triad of SS and the correct diagnosis. The DWI appearance of SS may not have been described before, but our findings would be consistent with the pathological process of small arteriolar occlusion and microinfarction of the brain. [2] The MRI pattern and ophthalmic findings in SS are similar to our prior experience with Nipah virus encephalitis, a rare pig-borne infection that also resulted in branch retinal artery occlusion and identical small DWI lesions within the white matter, including corpus callosum. [3] Our observation of DWI abnormalities in both SS and Nipah virus infection probably reflects similar ischemic pathology. [4] Although hyperintense lesions on DWI are typical of acute cerebral infarction, they are not common in MS. This distinction may be clinically relevant as typical MRI findings in SS are often misinterpreted as MS. DWI may be useful in the differential diagnosis of SS, especially among patients in whom the triad is absent. Figure 1 Figure 2 Fig 1 T2-weighted MR image showing multiple small hyperintensities in the corpus callosum (arrow) and white matter (arrowheads). Fig 2 On corresponding diffusion-weighted image, the lesions show high signal intensity (arrow and arrowheads). References 1. Susac JO, Murtagh FR, Egan RA, et al. MRI findings in Susac’s syndrome. Neurology 2003;61:1783-1787. 2. Monteiro ML, Swanson RA, Coppeto JR, Cuneo RA, DeArmond SJ, Prusiner SB. A micoangiopathic syndrome of encephalopathy, hearing loss, and retinal arteriolar occlusions. Neurology 1985;35:1113-21. 3. Lim CC, Lee WL, Leo YS, et al. Late clinical and magnetic resonance imaging follow up of Nipah virus infection. J Neurol Neurosurg Psychiatry 2003;74:131-133. 4. Lim CC, Lee KE, Lee WL, et al. Nipah virus encephalitis: serial MR study of an emerging disease. Radiology 2002;222:219-26.