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CASE REPORT
Year : 2015  |  Volume : 63  |  Issue : 6  |  Page : 915-917

Neurocognitive impairment in Susac syndrome: Magnetic resonance imaging and Tc-99m hexamethylpropyleneamine oxime single photon emission computed tomography correlation


Department of Medical Imaging, The Townsville Hospital, Douglas, Queensland, Australia

Date of Web Publication20-Nov-2015

Correspondence Address:
Dalveer Singh
Department of Medical Imaging, The Townsville Hospital, Douglas, Queensland 4102
Australia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0028-3886.170076

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 » Abstract 

Susac syndrome is a clinical triad of branch retinal artery occlusions, sensorineural hearing loss, and encephalopathy. The characteristic central corpus callosum involvement in Susac syndrome is readily recognizable on conventional magnetic resonance imaging (MRI); however, the neurocognitive effect of these lesions is not well-understood. We present a case of Susac syndrome with typical MRI findings of central callosal lesions at diagnosis. The patient had a protracted clinical course and did not respond well to immunosuppression therapy. Follow-up brain single photon emission computed tomography with Tc-99m hexamethylpropyleneamine oxime revealed marked unilateral frontoparietal and temporal lobe hypoperfusion. Our case highlights the utility of functional neuroimaging to uncover the possible underlying white matter dysfunction, which is not otherwise detectable with conventional MRI techniques.


Keywords: Corpus callosum; single photon emission computed tomography; Susac syndrome; Tc-99m hexamethylpropyleneamine oxime


How to cite this article:
Singh D, Hsu CC. Neurocognitive impairment in Susac syndrome: Magnetic resonance imaging and Tc-99m hexamethylpropyleneamine oxime single photon emission computed tomography correlation. Neurol India 2015;63:915-7

How to cite this URL:
Singh D, Hsu CC. Neurocognitive impairment in Susac syndrome: Magnetic resonance imaging and Tc-99m hexamethylpropyleneamine oxime single photon emission computed tomography correlation. Neurol India [serial online] 2015 [cited 2019 Dec 11];63:915-7. Available from: http://www.neurologyindia.com/text.asp?2015/63/6/915/170076



 » Case Report Top


A 45-year-old female patient presented to the emergency department in an acute state of confusion on a background of major depression diagnosed 16 months ago. On assessment, she was profoundly disorientated, showed expressive dysphagia, and family members reported her declining short-term memory over several months. Neurological examination was pertinent for reduced visual acuity on the right to 20/70 compared to 20/20 on the left. Normal tone, reflexes, and power were observed in the upper and lower limbs. Sensation and proprioception were also intact. Magnetic resonance imaging (MRI) of the brain showed multiple rounded T2 hyperintense lesions in the body and splenium of the corpus callosum [Figure 1]a and [Figure 1]b. On the T1 sagittal image, these lesions were hypointense and situated within the central layer of the corpus callosum [Figure 1]c. The differential considerations at this point included primary demyelination, vasculitis, and, in particular, the central location of lesions within the callosal fibers raised the possibility of Susac syndrome. This prompted audiometric evaluation, which revealed the bilateral low-frequency sensorineural hearing loss. Retinal fluorescein angiography showed peripheral retinal arteriolar branch occlusions in the right eye. Despite the partial response to corticosteroid therapy, there were residual cognitive impairments affecting memory and concentration. Follow-up MRI at 6 months showed no interval change in the morphology of the existing lesion and no new lesion was detected. Given the persistent cognitive impairment, single photon emission computed tomography (SPECT) scan of the brain with Tc-99m hexamethylpropyleneamine oxime [HMPAO] (CERETEC ®) SPECT was performed. It showed a marked reduction in the cerebral blood flow in the right frontoparietal and temporal lobes despite the presence of a symmetric brain volume [Figure 2].
Figure 1: Magnetic resonance imaging brain axial T2-weighted images (a and b) showing multiple rounded hyperintense lesions ranging in size from 5 mm to 10 mm in the body and splenium of corpus callosum (white arrows). Sagittal T1-weighted image (c) showing discrete hypointense lesions within the central layer of the corpus callosum

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Figure 2: Serial axial Tc-99-labeled hexamethylpropyleneamine oxime single photon emission computed tomography images showing a marked reduction in the cerebral blood flow in the right frontotemporal and parietal lobes despite the presence of symmetric brain volume. There is a symmetric tracer uptake in the cerebellum

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 » Discussion Top


Susac syndrome is the clinical triad of retinal arteriolar branch occlusions, sensorineural hearing loss, and subacute encephalopathy, with predominantly cognitive impairment, memory loss, and psychiatric symptoms.[1],[2],[3] This rare condition predominantly affects females in the third to fifth decades.[2] The pathophysiological basis is hypothesized to be an autoimmune-mediated occlusive endotheliopathy involving arterioles (<100 µm) in the retina, cochlea, and brain causing microinfarcts.[4] Patients do not always present with the classical triad, and the degree of neurological disturbance can be variable.[2],[5] Brain MRI findings in Susac syndrome can show both gray and white matter lesions, with basal ganglia and thalamic lesions seen in up to 70% of cases. Parenchymal lesions in the acute phase can demonstrate gadolinium enhancement, while leptomeningeal enhancement is less frequently observed.[1] White matter lesions in Susac syndrome can resemble multiple sclerosis (MS) or acute disseminated encephalomyelitis. A distinctive feature of Susac syndrome, however, is that it almost always involves the central callosal fibers, which are predisposed to arterial microinfarcts.[2] On the contrary, plaques in MS are seen on the ependymal under-surface of the corpus callosum along venous drainage pathways. A recent 7T MRI study comparing MS and Susac syndrome has found key differences in lesion morphology on T2*-weighted sequences, namely the presence of a hypointense rim at the edges of MS plaques, which is not seen in Susac syndrome.[6] The significance of these callosal lesions in Susac syndrome and their relation to the observed neurocognitive impairment is not well-understood. A recent diffusion tensor imaging study in Susac syndrome revealed damage to the callosal fiber integrity and prefrontal white matter, which correlated much better with the clinical severity of encephalopathy than the conventional MRI findings.[7] Brain perfusion and metabolism alterations are yet to be fully investigated in Susac syndrome, with only one reported case showing unilateral decreased cerebral glucose metabolism utilizing fluorine 18-fluorodeoxyglucose positron emission tomography, which resolved with treatment.[8] Interestingly, our case showed markedly reduced unilateral cerebral hemispheric perfusion with Tc-99 HMPAO SPECT. The significance of this finding is not entirely clear; however, the reduced cerebral perfusion in the right hemisphere may be secondary to callosal fiber disruption. This is supported by similar findings of reduced cerebral perfusion and glucose metabolism in other pathologies affecting the corpus callosum such as large anterior corpus callosal infarct,[9] callosal hematoma,[10] and Marchiafava-Bignami disease.[11],[12],[13],[14] The neurocognitive disturbance reported in Susac syndrome, in particular the frontotemporal executive functions, may be due to macroscopic axonal disruption of the corpus callosum as described above, or due in part to microscopic arteriolar endotheliopathy beneath current imaging resolution. Long-term outcomes in Susac syndrome are not well known and rely upon small case series with variable follow-up. The spectrum of reported neurological deficits ranges from behavioral or personality changes, memory, concentration or mild cognitive disturbance, ataxia, and weakness. The largest long-term follow-up case series (mean follow-up 6.4 years) in 9 patients found no correlation between the initial severity of encephalopathy and the long-term neurocognitive decline, which was seen in half the patients at final follow-up.

Callosal lesions in Susac syndrome may well represent the "the tip of iceberg" for greater underlying white matter dysfunction. Further functional neuroimaging studies may improve understanding of the neurocognitive impairment in Susac syndrome and potentially aid in the assessment of response to immunosuppressive therapy.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
 » References Top

1.
Susac JO. Susac's syndrome. AJNR Am J Neuroradiol 2004;25:351-2.  Back to cited text no. 1
[PUBMED]    
2.
Dörr J, Krautwald S, Wildemann B, Jarius S, Ringelstein M, Duning T, et al. Characteristics of Susac syndrome: A review of all reported cases. Nat Rev Neurol 2013;9:307-16.  Back to cited text no. 2
    
3.
Dörr J, Ringelstein M, Duning T, Kleffner I. Update on Susac syndrome: New insights in brain and retinal imaging and treatment options. J Alzheimers Dis 2014;42 Suppl 3:S99-108.  Back to cited text no. 3
    
4.
Magro CM, Poe JC, Lubow M, Susac JO. Susac syndrome: An organ-specific autoimmune endotheliopathy syndrome associated with anti-endothelial cell antibodies. Am J Clin Pathol 2011;136:903-12.  Back to cited text no. 4
    
5.
Bardal RC, Badaro E, Arana J, Alves F, Souza EC, Bonomo PP, et al. Susac syndrome: Diverse clinical findings and treatment. Arq Bras Oftalmol 2014;77:188-90.  Back to cited text no. 5
    
6.
Wuerfel J, Sinnecker T, Ringelstein EB, Jarius S, Schwindt W, Niendorf T, et al. Lesion morphology at 7 Tesla MRI differentiates Susac syndrome from multiple sclerosis. Mult Scler 2012;18:1592-9.  Back to cited text no. 6
    
7.
Kleffner I, Deppe M, Mohammadi S, Schiffbauer H, Stupp N, Lohmann H, et al. Diffusion tensor imaging demonstrates fiber impairment in Susac syndrome. Neurology 2008;70:1867-9.  Back to cited text no. 7
    
8.
Dielman C, Laureys G, Meurs A, Bissay V, Ebinger G. Susac syndrome: A case report and PET imaging findings. Acta Neurol Belg 2009;109:226-30.  Back to cited text no. 8
    
9.
Andreadou E, Papadimas GK, Sifakis N, Sfagos C. Corpus callosum infarct associated with combined variants in circle of Willis. Neurol India 2010;58:785-6.  Back to cited text no. 9
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10.
Kim IH, Lee S, Lee CY, Lee DG. Intracranial hemorrhage in the corpus callosum presenting as callosal disconnection syndrome: FDG-PET and tractography: A case report. Ann Rehabil Med 2014;38:871-5.  Back to cited text no. 10
    
11.
Ferracci F, Conte F, Gentile M, Candeago R, Foscolo L, Bendini M, et al. Marchiafava-Bignami disease: Computed tomographic scan, 99mTc HMPAO-SPECT, and FLAIR MRI findings in a patient with subcortical aphasia, alexia, bilateral agraphia, and left-handed deficit of constructional ability. Arch Neurol 1999;56:107-10.  Back to cited text no. 11
    
12.
Ishii K, Ikerjiri Y, Sasaki M, Kitagaki H, Mori E. Regional cerebral glucose metabolism and blood flow in a patient with Marchiafava-Bignami disease. AJNR Am J Neuroradiol 1999;20:1249-51.  Back to cited text no. 12
    
13.
Nalini A, Kovoor JM, Dawn R, Kallur KG. Marchiafava-Bignami disease: Two cases with magnetic resonance imaging and positron emission tomography scan findings. Neurol India 2009;57:644-8.  Back to cited text no. 13
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14.
Bhat A, Punia V, Lee HJ, Marks D. Corpus callosum fibre disruption in Marchiafava-Bignami disease. Pract Neurol 2014;14:189-90.  Back to cited text no. 14
    


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