Subacute sclerosing panencephalitis (SSPE), also known as Dawson disease, is a rare chronic, progressive and fatal encephalitis that affects primarily children and young adults, caused by a persistent infection of immune resistant measles virus.
1 in 100,000 people infected with measles develop SSPE, with a latency of typically a decade (range 4-23 years) and thus a typical age of onset of 9-13 years of age . The marked decline of SSPE in first world nations is yet another example of the benefit of widespread vaccination.
Clinical presentation is gradual, progressive neuropsychological deterioration, consisting of personality change, seizures, myoclonus, ataxia, photosensitivity, ocular abnormalities, spasticity, and coma.
Histopathologically, SSPE demonstrates the same changes seen in other chronic viral cerebral infections, such as HIV encephalitis and post-infectious encephalomyelitis .
CSF analysis may show elevated levels of:
- anti-measles antibodies
- periodic slow-wave complexes are characteristic
Features depend on the stage of disease. In the acute setting, patchy asymmetric regions of white matter involvement are present, typically in the temporal and parietal lobes. Mild reduction in grey matter involving predominately the amygdala, frontotemporal cortex, and cingulate gyrus can also be seen in the early stage of the disease . Gradually more extensive white matter involvement develops with additional involvement of the corpus callosum and basal ganglia. Eventually, a generalized encephalomalacia develops and parenchymal loss may be seen in later stages.
- T2/FLAIR: high signal within white matter in the parietal and temporal lobes in the acute stage
- T1 C+ (Gd): enhancement of affected regions may occur early in the course of the disease.
- MR spectroscopy may demonstrate
- decreased NAA: from neuronal loss
- increases in choline: from demyelination
- increase myo-inositol: from active gliosis
- elevated lactate: from macrophagic infiltration