The patient underwent a biopsy via burrhole.
Paraffin sections show small fragments of cerebral cortex and white matter. The cortex appears unremarkable. Luxol Fast Blue staining shows several areas with reduced myelin density which are sharply demarcated from adjacent white matter with intact myelin. Within these demyelinated areas there are large numbers of CD68+ monocyte-macrophages with strong surface expression of MHC Class II. Granular LFB+ myelin debris is noted within the cytoplasm of these cells. Activation of microglia with strong MHC Class II expression is also noted. Small calibre blood vessels are surrounded by narrow cuffs of T lymphocytes (CD4>CD8). No viral inclusion bodies are identified. There is no evidence of tumour. The features are of inflammatory demyelination.
FINAL DIAGNOSIS: inflammatory demyelination.