FIG 2. Biopsy specimens.

A, In the biopsy fragments, the cerebral white matter shows a normal aspect with ample staining for myelin, absence of inflammatory infiltrate and (in contrast to PML) absence of enlarged nuclei of glial cells. Occasional perivascular macrophages (arrow), however, contain granular, blue-staining material, consistent with myelin debris. (Combined Luxol Fast Blue and Hematoxylin-Eosin staining; original magnification x630).

B, Electron microscopy, performed on material retrieved from the paraffin block, reveals multilamellar particles in the perivascular macrophages, corroborating the myelin nature of these granules.