Subacute sclerosing panencephalitis with bilateral inferior collicular hyperintensity on magnetic resonance imaging brain.

Subacute sclerosing panencephalitis (SSPE) is chronic encephalitis occurring after infection with measles virus. An 8-year-old boy presented with progressive behavioral changes, cognitive decline and myoclonic jerks, progressing to a bed bound state over 2 months. Magnetic resonance imaging (MRI) brain showed T2-weighted hyperintensities in the subcortical areas of the left occipital lobe and brachium of the inferior colliculus on both sides. EEG showed bilateral, synchronous periodic discharges. Serum/cerebrospinal fluid measles IgG titer was significantly positive. The overall features were suggestive of SSPE. MRI finding of bilateral inferior colliculus changes on MRI without significant involvement of other commonly involved areas suggests an uncommon/rare imaging pattern of SSPE.

Introduction

Subacute sclerosing panencephalitis (SSPE), first described by Dawson (1934), is chronic encephalitis due to persistent infection of the brain by an aberrant measles virus. Magnetic resonance imaging (MRI) is the most sensitive imaging modality in SSPE.[1] Based on the previous reports, commonly involved areas are cerebral cortical, periventricular and subcortical regions. The basal ganglia, cerebellum, spinal cord and callosum are less commonly involved. Brainstem involvement is rare.[1-3] In this article, we describe the MRI findings of a patient with SSPE having inferior collicular involvement without significant involvement of other structures, which has not been described in previous reports.

Case Report

An 8-year-old boy presented with behavioral changes, poor school performance, speech deterioration, recurrent falls, urinary incontinence and, later, fluctuating sensorium and myoclonic jerks evolving over 2 months to a bed bound state with altered sensorium (Clinical stage III). In addition, he had bilateral pyramidal signs. He had history suggestive of measles 3 years back. MRI brain showed T2-weighted hyperintensities in the subcortical areas of the left occipital lobe and brachium of the inferior colliculus on both sides. These abnormal areas showed increased signal intensity of diffusion-weighted images (DWI). Other areas were normal [Figure 1]. EEG showed synchronous, periodic bursts of sharp and slow wave complexes bilaterally, lasting for a period of 3–4 s and occurring at regular intervals of about 6 s. Cerebrospinal fluid (CSF) showed 2 cells/cumm (all lymphocytes), 23 mg% proteins and 62 mg% glucose, without atypical cells. CSF polymerase chain reaction (for Herpes, EBV, Cytomegalo, Varicella and Adeno viruses) was negative. CSF measles serology was significantly positive (serum/CSF measles IgG titer ratio was 20, ratio of <64 is considered significant). Overall features were suggestive of fulminant SSPE, but with atypical brain imaging features.

Figure 1

T2 and flair axial magnetic resonance images of the brain showing hyperintensity in the left occipital region (a and d, arrows) and brachium of inferior colliculus bilaterally (b and e, arrows), also seen on the T2 coronal image (c, arrows), with increased signal intensity on diffusion-weighted images (f, arrows)

Discussion

SSPE is diagnosed based on the clinical assessment, EEG findings and elevated serum and CSF antimeasles antibody titers.[12] Brain imaging is not needed for the diagnosis nor has an impact on the outcome, but can show the evolution/extent of the disease, and for differential diagnosis.[1-3] MRI abnormalities in SSPE include symmetrical, focal areas of increased signal intensity on T2 and hypo- or isointense on T1-weighted images. Changes are common in the cerebral cortex, subcortical and periventricular white matter and less common in the corpus callosum, basal ganglia, cerebellum and thalamus. They are rare in the brainstem.[1-3] Lesions usually start appearing in the occipital region and then progress to involve the frontal cortex; subsequently, the subcortical white matter, basal ganglia, thalamus and corpus callosum are involved. Later, progressive cortical atrophy is seen.[4] MRI can be normal or may show asymmetric changes in the early stages of the disease, and changes do not always correlate with the clinical stage.[4] In our patient, the progressive nature of illness with myoclonus, characteristic EEG pattern and presence of raised antimeasles antibody titers in CSF confirmed the diagnosis of SSPE. His MRI brain [Figure 1] showed subtle T2-weighted hyperintensities in the subcortical areas of the left occipital lobe, this again going with the findings in the previous reports that changes can be asymmetric and need not correlate with the clinical stage.[4] Our patient also had bilateral symmetrical T2 hyperintensities in the brachium of the inferior colliculus, with increased signal intensity on DWI [Figure 1]. Brain stem involvement is very rare and is reported only in association with the other intracranial lesions.[12] Yilmaz et al. reported two patients with brainstem involvement, one patient with prominent pontine involvement in addition to involvement of subcortical white matter involvement, cortical areas of the occipital lobes, corpus callosum and splenium. The other patient had initial normal imaging and later developed lesions in the Pons and Cerebellar peduncles.[1] Brismar et al. reported pontine involvement in two of the 52 patients with SSPE they evaluated. One patient who already had disease elsewhere in the brain developed pontine lesions during follow-up; the other had severe changes in the brainstem, cerebral peduncles and Pons, but normal appearance in the cortex.[3] Sharma et al. reported prominent pontine and middle cerebellar peduncle involvement in addition to cerebral lesions in a 15-year-old boy with SSPE.[4] Kalane et al. reported extensive brainstem and cerebellum involvement with additional lesion in the basal ganglia in a child with SSPE, which was initially diagnosed as low-grade Glioma.[5] Cece et al. reported brainstem involvement in three of the 76 patients with SSPE they evaluated.[6] These reports highlighted brainstem involvement, mainly of the Pons and peduncles, demonstrating that SSPE should be considered in the differential diagnosis of brainstem lesions observed on MRI in appropriate clinical settings. Differential diagnosis for posterior fossa lesions on MRI brain include inflammatory conditions (multiple sclerosis, acute disseminated encephalomyelitis, Behçet's disease, neurosarcoidosis, connective tissue disorders), infections (Lyme disease, progressive multifocal leukoencephalopathy, Whipple's disease, listeria rhombencephalitis), Bickerstaff's brainstem encephalitis, tumors (pontine gliomas and lymphomas), histiocytosis, vascular ischemic lesions, central pontine myelinolysis, diffuse axonal injury, radiation-induced lesions and leukoencephalopathies. In leukoencephalopathies, signal abnormalities are rarely as prominent as the supratentorial abnormalities. Cerebellar white matter abnormalities are often seen in peroxisomal disorders, Alexander disease, leukoencephalopathy with brainstem and spinal cord abnormalities (LBSL) and early-onset maple syrup urine disease. Prominent brainstem abnormalities are usually seen in Alexander disease, LBSL and adult polyglucosan disease.[78] MRI finding of bilateral inferior colliculus involvement has not been hitherto reported in the literature, and this suggests an uncommon/rare imaging pattern of SSPE. The present case and the previous reports discussed widen the spectrum of imaging features seen in SSPE.

Conclusion

Although SSPE commonly involves the periventricular white matter, basal ganglia, thalamus and corpus callosum, brainstem involvement is being increasingly described, at times without significant changes in the other areas. SSPE should be considered as a differential diagnosis when dominant brainstem abnormalities are seen on neuroimaging in a patient with typical clinical and EEG findings.