The patient went on to have a right frontal lobe brain biopsy.
Histology:
The biopsies comprise predominantly fragments of unremarkable cerebral cortex with a small amount of underlying white matter. Within the white matter there is widening of perivascular spaces and these are filled with moderate numbers of predominantly CD8+ T lymphocytes. Small numbers of CD4+ T cells and moderate numbers of CD68+ monocyte-macrophages are also present. CD8+ T cells are also scattered throughout white matter. There is prominent microglial activation. There is reduced density of myelin in white matter adjacent to post-capillary venules with mild myelin loss. Vessels are viable and there is no neutrophil polymorphonuclear inflammatory cell infiltration and no haemorrhages are seen. No organisms are identified. Immunostaining for SV40/BKV is negative. There is no evidence of tumour.
Final diagnosis: The features are consistent with acute disseminated encephalomyelitis (ADEM).