Patients (mainly, but not exclusively, children) pass through a prodromal period of minor signs and symptoms, followed by the acute stage, characterized by progressive decline of functions associated with the affected hemisphere (hemiparesis, hemianopia, cognitive deterioration and/or aphasia), as well as seizures. About 50% of patients experience epilepsia partialis continua: unilateral myoclonic twitching of the distal extremities or the face for at least 1 hour with intervals of no more than ten seconds. The patient passes into the residual phase of stable neurological deficit and decreased frequency of seizures after about 8 months.
Pathologically, there is infiltration of T lymphocytes. Cytotoxic T-cells are thought to lead to apoptosis of neurons and astrocytes.
Imaging shows progressive unilateral (usually precentral and inferior frontal) atrophy. CT and MRI are often initially normal, followed by findings of cortical swelling and then atrophy. FLAIR may show small areas of hyperintensity that increase over time. MR spectroscopy shows decreased NAA and choline and increased myoinositol and glutamine/glutamate.
Functional imaging (e.g., PET) may reveal decreased activity in the affected lobe(s) or hemisphere when MRI is normal. PET and SPECT may also show crossed cerebellar diaschisis.
Differential considerations include:
- Sturge-Weber syndrome: Also will see progressive hemispheric atrophy, but there may be cortical calcifications and enhancing of pial angiomas. Clinically, there is a port wine facial nevus.
- MELAS: Mitochondrial encephalopathy, lactic acidosis, and strokelike episodes. Will see cortical atrophy in the chronic phase. Look for lacunar infarctions.
- Hemispheric infarction (Dyke-Davidoff-Masson): Will also have unilateral atrophy, but there may be compensatory calvarial thickening, elevation of the petrous ridge and hyperaeration of the paranasal sinuses.
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