The patient went on to have a stereotactic biopsy from the frontal lobe.
Paraffin sections show cores of cerebral white matter. These show prominent perivascular cuffs of small lymphoid cells which are a mixture of CD3+ T lymphocytes and CD20+ B lymphocytes. Smaller numbers of CD68+ monocyte-macrophages are also present in these perivascular aggregates. Vessel walls are intact. There is expansion of perivascular spaces. In one of the cores in specimen 2 there is a well-demarcated area of demyelination. Many monocyte-macrophages containing cytoplasmic myelin debris are seen in this area. There is activation of microglial cells. The overall features strongly favour inflammatory demyelination. Immunostaining for SV-40/JC/BKV is negative. No organisms are identified and there is no evidence of tumour.
Stereotactic brain biopsies: Features strongly suggestive of inflammatory demyelination; no evidence of tumour seen.