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|LETTER TO EDITOR
|Year : 2015 | Volume
| Issue : 3 | Page : 452-456
Diffusion restriction in fulminant subacute sclerosing panencephalitis: Report of an unusual finding
Dhaval Shah1, K Srinivasan1, Tejas Sakale2, S Sajith2, C Kesavadas1
1 Department of Imaging Sciences and Interventional Radiology, Sree Chitra Thirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala, India
2 Department of Neurology, Sree Chitra Thirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala, India
|Date of Web Publication||5-Jun-2015|
Department of Imaging Sciences and Interventional Radiology, Sree Chitra Thirunal Institute for Medical Sciences and Technology, Trivandrum, Kerala
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Shah D, Srinivasan K, Sakale T, Sajith S, Kesavadas C. Diffusion restriction in fulminant subacute sclerosing panencephalitis: Report of an unusual finding. Neurol India 2015;63:452-6
|How to cite this URL:|
Shah D, Srinivasan K, Sakale T, Sajith S, Kesavadas C. Diffusion restriction in fulminant subacute sclerosing panencephalitis: Report of an unusual finding. Neurol India [serial online] 2015 [cited 2020 Feb 28];63:452-6. Available from: http://www.neurologyindia.com/text.asp?2015/63/3/452/158268
Subacute Sclerosing Panencephalitis (SSPE) is a fatal progressive encephalitis caused by abnormal persistence of the measles virus infection in the central nervous system.  SSPE usually occurs in young children and adolescents; however, it is also known to affect adults and pregnant women. The clinical picture is characterized by behavioural abnormalities, cognitive decline, myoclonic epilepsy and seizures.  Diagnosis of SSPE is dependent upon a combination of clinical features, characteristic EEG abnormalities and elevated antimeasles antibody titre in the serum and the CSF.  MRI findings in SSPE have been described in previous studies. ,,,, We report a patient of fulminant SSPE who showed atypical MRI findings on serial diffusion weighted sequences.
A 15-year old girl presented with a 5 month history of slowly progressive cognitive decline characterized by behavioural changes, slowing of daily activities and deterioration of handwriting. She also had intermittent, involuntary jerky movements of head and bilateral upper limbs for 4 months. Initially, she was evaluated at another centre with a cranial MRI which showed hyperintensities on T2 FLAIR sequences involving the cortex and the subcortical white matter in the right temporal and the left parieto-occipital lobes without any diffusion restriction or contrast enhancement. However, no specific treatment was initiated at that time. One month later, the girl developed 4 episodes of seizures and was re-admitted. Repeat MRI showed new T2W hyperintense lesions in the right parieto-occipital lobes without any significant diffusion restriction or contrast enhancement. The lesions seen in the previous scan had become less conspicuous by this time. Suspecting a demyelinating pathology, the patient was treated with intravenous methylprednisolone followed by oral steroids to which she showed partial improvement. However, over the next 2-3 weeks, there was a symptomatic relapse with increasing myoclonic jerks and apathy. She was admitted at our centre this time, about 5 months into the illness, with paucity of left upper and lower limb movements which progressed to complete paralysis over the next 3 days. There was no significant past medical history including any history of measles in the childhood. The vaccination status for measles was also uncertain. Clinical examination revealed apathy, a MMSE score of 20, mild dysarthria, left UMN facial palsy with left hemiplegia (MRC grade I). The laboratory findings revealed elevated measles antibody titres both in the serum (>250 IU/ml) and in the CSF (1:625). Her vasculitic profile and serological markers for autoimmune encephalitis were negative. Her EEG showed characteristic long interval periodic complexes [Figure 1].
|Figure 1: Electroencephalography (EEG) findings of the patient. (a) Sixteen channel EEG recording (with sensitivity of 7 μV/mm and paper speed of 10 s/ page) shows the classical generalized long-interval periodic complexes (Rademecker's complex) composed of delta and admixed spike and wave activity at an interburst interval of 3.5 s, seen throughout the record. The interburst interval shows attenuated background with superimposed theta-delta slowing asymmetrically expressed, more over the right hemisphere. (b) Same EEG at 30 s/page shows the periodicity more clearly|
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A repeat MRI of the brain showed new FLAIR hyperintensities, albeit with patchy restricted diffusion, in the right frontal lobe. Hyperintensities were also seen in bilateral posteromedial thalami [Figure 2]. The clinical presentation, elevated measles antibody titres, EEG and MRI findings were consistent with probable SSPE as per Dyken's criteria. Meanwhie, the patient's sensorium continued to decline with development of marked dysautonomia requiring ventilatory and hemodynamic support. Repeat MRI showed multifocal cortical swelling and FLAIR hyperintensities involving bilateral frontal, parietal and temporal lobes. Extensive confluent hyperintensities were also noted involving bilateral centrum semiovale, corona radiata, external capsule, posterior limb of the internal capsule, corpus callosum, hypothalami and the subcortical white matter of bilateral frontal and occipital lobes. All the lesions showed restricted diffusion with very low ADC values except for the right frontal lobe lesion which showed facilitated diffusion [Figure 3].
|Figure 2: Magnetic resonance imaging at 5 months after the onset of symptoms. Axial fluid-attenuated inversion recovery images (a and b) show hyperintensities involving the cortex and subcortical white matter of right frontal lobe and bilateral thalami. Diffusion weighted trace (c) and apparent diffusion coefficient map (d) shows restricted diffusion involving both gray and white matter|
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|Figure 3: Follow-up imaging. Axial fluid-attenuated inversion recovery (a) images show confluent hyperintensities involving bilateral fronto-parietal lobes. Coronal T2-weighted image (b) shows involvement of the left temporal lobe, bilateral basal ganglia and external capsule. Diffusion weighted (DW) trace (c) and apparent diffusion coefficient (ADC) map (d) shows restricted diffusion in bilateral internal capsules, subcortical white matter of right frontal and bilateral occipital lobes. DW trace and ADC map (e and f) at higher level show confluent areas of restricted diffusion in bilateral centrum semiovale. Areas of increased ADC are noted in the right frontal lobe|
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Clinically, the patient continued to deteriorate and eventually succumbed to her illness.
The various neurological complications of measles infection include post measles encephalitis, measles inclusion body encephalitis, SSPE and transverse myelitis.  SSPE is a rare neurodegenerative disease characterized by a chronic persistent progressive encephalitis. The patients generally have a history of measles infection prior to the age of 2 years followed by a latent period of about 6-8 years before SSPE sets in. SSPE has got a variable natural history ranging from an acute onset fulminant illness resulting in death within a few weeks to 6 months, to a more insidious onset, slowly progressive disorder with multiple remission and relapses. Our patient had an atypical presentation with a fulminant clinical course leading to death within 6 months of the disease onset. Such a natural history has been noted in about 10% of the cases.  Even though our patient had no clinically documented attack of measles in the past, the occurrence of SSPE can be explained by a possible subclinical measles infection before the age of 1 year which is rather common in our country. ,
In the early stages of SSPE, MRI shows asymmetric T2/FLAIR hyperintensities involving the cortex and the subcortical white matter bilaterally with predominant parieto-occipital lobe involvement. The lesions may show resolution with time and on follow-up imaging, new lesions may appear with gradually progressive cortical volume loss. In the advanced stages, there is more widespread involvement of the deep periventricular white matter. Rarely, lesions have also been described involving the corpus callosum, brainstem, thalamus, cerebellum and even the spinal cord.  Similar imaging findings were also noted in our case with migratory cortical-subcortical white matter lesions in the early stages and involvement of deep white matter, corpus callosum, thalami and brain stem in the later stages. Studies have shown a poor correlation between the clinical status and the cranial imaging appearance in SSPE. 
Few studies till date have described the role of diffusion weighted imaging in SSPE. ,, Majority of them have demonstrated increased ADC values in the involved cerebral parenchyma. Alkan et al.  correlated the clinical stage of the disease with the diffusion weighted MRI findings. They found that the ADC values progressively increased with the advancing clinical stage of the disease. The histopathological correlates of increased diffusion include demyelination, neuronal loss and parenchymal necrosis.
Diffusion restriction is a widely documented finding in acute measles encephalitis and suggests the cytotoxic edema in these cases.  However, diffusion restriction has not been previously reported in lesions of SSPE. Hideaki et al.  studied serial DWI findings in a case of SSPE. They demonstrated that reduction in the ADC values in the frontal lobe white matter correlated with clinical progression of disease. However, no ADC changes were noted in the gray or white matter lesions in their case. Oguz et al.  reported DWI findings in two cases of rapidly progressive SSPE. In one of their cases, there was increased diffusion in all the lesions with subtle restricted diffusion at their margins. In the other case, symmetric restricted diffusion was noted in bilateral middle cerebellar peduncles which the authors attributed to the pontocerebellar degeneration secondary to the pontine lesions.
Our case was peculiar in that the restriction in diffusion was extensive and involved bilateral cerebral hemispheric white matter, internal capsule, thalami and midbrain. This pattern of restricted diffusion is probably due to cytotoxic or intramyelinic edema secondary to the necrotizing leucoencephalopathy. Though SSPE is classically described as a chronic encephalitis, the fulminant form can have acute necrotizing encephalitis like presentation. Mahadevan et al.  reported a case of fulminant SSPE with histopathological findings of necrotizing leukoencephalitis showing diffuse demyelination and foci of cavitation. Further, the right frontal lobe lesion which showed diffusion restriction in the initial scan was showing increased ADC on follow-up imaging. The reason for the occurrence of transient cytotoxic edema with subsequent resolution into vasogenic edema remains unclear. We speculate that active demyelination is followed by astrogliosis and neuronal loss which may be responsible for the increased ADC. Further studies evaluating the serial DW images in cases having a fulminant SSPE with histopathological correlation are required for a better understanding of the progression of imaging findings.
To conclude, we have reported a case of fulminant SSPE with atypical MRI features of extensive diffusion restriction.
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[Figure 1], [Figure 2], [Figure 3]