MICROSCOPIC DESCRIPTION: 1-3. Sections show white matter mostly replaced by diffuse sheets of CD68+/CD1a-/S100- foamy macrophages containing intracytoplasmic granular material (Luxsol Fast Blue positive, consistent with myelin). The Neurofilament stain demonstrates associated axonal loss. There are small perivascular cuffs of CD3+ T-cells present (CD8>CD4). No vasculitis is seen. The GFAP stain highlights reactive astrocytes. The SV40/BK immunostain is negative for JC virus. No viral inclusions or granulomas are seen. The IDH-1 stain is negative. There is no evidence of tumour.
DIAGNOSIS: 1-3. Brain, right thalamic lesion: Features favouring inflammatory demyelination; no tumour seen.