Subacute sclerosing panencephalitis : CT and MR imaging in a rapidly progressive case.

M Alexander, S Singh, C Gnanamuthu, S Chandi, IP Korah 
 Departments of Neurosciences, Radiodiagnosis and Pathology, Christian Medical College and Hospital, Vellore, Tamilnadu, 632004, India., India

Correspondence Address:
M Alexander
Departments of Neurosciences, Radiodiagnosis and Pathology, Christian Medical College and Hospital, Vellore, Tamilnadu, 632004, India.
India

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::   Introduction

SSPE is a slowly progressive disorder that is typically seen in children and adolescents with an invariably fatal outcome. It is a unique slow viral disease in which the measles virus has been identified as the pathogen. The usual age of onset is between 5-12 years.[1],[2],[3],[4] The natural history of SSPE is characterized by a highly variable temporal course ranging from an almost acute onset with rapid progression and death within a few weeks, to a protracted course after several years with phases of stabilization and even improvement.[3],[4],[5] The diagnosis is usually established by the clinical manifestation, presence of abnormal complexes on EEG, laboratory findings including high levels of CSF gamma globulin, and elevated titer of measles antibody in the CSF and serum.[1],[2],[3],[4],[5],[6],[7] Generally, CT and MR imaging characteristics do not correlate with progression of the disease.[6],[7],[8] Our patient showed a rapid radiological evolution that correlated with the progression of the disease.

::   Case report

A 17-year-old male presented with a rapidly progressive neurological syndrome characterized by spasticity, very infrequent myoclonic jerks and dystonic posturing of the right upper limb of 1 month's duration and three episodes of generalized seizures. There was no history of measles in childhood, nor was he immunized against the disease. He was stuporous with a Glasgow Coma Scale of 10/15 (E4 V1 M5). Measles antibody titer revealed a Serum: CSF ratio of 40:1, which was suggestive of SSPE. The other antibody titers were unremarkable. CT imaging of the brain after 1 week into the illness was unremarkable [Figure. 1], however MR imaging revealed ill-defined slightly high signal intensity areas on T2-weighted images in the periventricular white matter and centrum semiovale bilaterally, predominantly involving the parietal lobes [Figure. 2]. On proton density weighted images, there was slight effacement of the gray-white matter definition. On T1-weighted images however, these lesions were not identified. EEG revealed periodic complexes and CSF showed lymphocytic pleocytosis (40 cells) with normal sugar and protein levels. While in the hospital he developed severe dystonia of all four limbs, opisthotonus, seizures, and dysautonomia. A CT repeated after 1 month revealed patches of ill-defined low density lesions with isolated enhancement in the cortical and subcortical white matter of the frontal and parietal lobes bilaterally [Figure. 1B]. A few lesions were also noted in the frontal periventricular white matter and centrum semiovale. MR imaging performed at this time demonstrated diffuse large high signal intensity lesions of varied sizes in the cerebrum bilaterally, involving the cortex, subcortical, deep and periventricular white matter, basal ganglia and thalami bilaterally, on T2-weighted and proton density weighted images [Figure. 3A].

On T1-weighted images, these lesions were of low signal intensity with loss of gray-white definition and obliteration of the sulci [Figure. 3B]. Since there was rapid clinical deterioration and CSF examination showed pleocytosis, which is very unusual in SSPE, a brain biopsy was advised. Microscopic examination of the biopsied brain tissue showed moderate perivascular infiltrates of lymphocytes as well as a few neutrophils and plasma cells in the cerebral cortex and white matter associated with neuronal depletion, widespread spongiosis, and gliosis as well as rarefaction of the white matter in areas. There were intranuclear homogenous eosinophilic inclusions in several glial cells chiefly astrocytes. The pia-arachnoid was also inflamed [Figure. 4]. He was treated with intrathecal interferon, 1 million units on alternate days for 15 days, and also with isoprinosine, carbamazepine, sodium valproate, clonazepam, and pacitane.

::   Discussion

SSPE is a fatal encephalitis of children and adolescents, associated with an episode of measles several years before the onset of encephalitis.[1],[2],[3],[4] Our patient had no definite past history of measles. Clinically, the classical disease takes 1 to 3 years to progress from stage I (mental and behavioral abnormalities) to stage IV (mutism, occasional myoclonus and loss of cortical function).[2],[4],[7] However, our patient rapidly deteriorated within 1 month to stage III of Risk and Haddad.[5] Correlation between radiological changes and clinical findings have been poor with normal MRI in bedridden patients or improvement despite clinical progression have been found.[7] Murata et al had reported serial MRI in a case that showed radiological improvement parallel to partial clinical improvement.[8] Brismar et al reported partial resolution of lesions inspite of clinical progression.[7] Though changes seen on CT and MRI are non-specific, MRI can be used to assess the extent of brain involvement in early stages of encephalitis as it is more sensitive. Depending on white matter changes and atrophy, Brismar et al classified radiological changes into 6 stages.[7] Neuropathological findings suggest that the disease initially affects the occipital cortex and then progresses to involve the frontal cortex and finally the subcortical white matter, brain stem, and spinal cord.[7]



As in this patient, early changes are detectable as ill-defined high signal intensity areas on T2-weighted images, more commonly in the occipital subcortical white matter than in the frontal region. In most of the cases the gray matter is spared even in advanced clinical and MRI stages.[7] In the later stage of disease high signal intensity lesions are better defined in both gray and white matter with loss of gray-white matter differentiation.[2] Cerebellar, pontine, thalamic and spinal cord involvement have been reported.[5],[7] On T1-weighted images, lesions are seen as low signal intensity.



In the early stage of the disease, the CT may be normal,[4],[7],[8] or may show slight cerebral oedema. In the later stages, however bilateral symmetrical or asymmetrical low-density enhancing or non-enhancing lesions in the cerebrum involving the gray and white matter[6],[7],[8] may be seen. Cortical atrophy is found in the advanced stages of disease.[2],[4],[6] Mass effect is not a feature in SSPE. Typically the lesions do not enhance,[2] however, our patient showed patchy enhancement on CT. Brismar et al have reported a case with rapid clinical progression which showed multiple areas of enhancement.[7] Contrast enhancement have also been reported in cases of relapse.[7] The findings in our patient concurred with this pattern.



Although measles antibody titer in serum and CSF was suggestive of SSPE in this patient, the rapid neurological deterioration and CSF pleocytosis warranted a brain biopsy to rule out other possibilities such as encephalitides of other etiologies. This case emphasizes the role of MR imaging in delineating early brain changes and their extent radiologically in SSPE, though the extent of the changes may or may not correlate clinically.

References