Figure 2

Brain biopsy. The biopsy specimen contained cortical grey and subcortical white matter with loose tissue texture (edema), fine caliber vacuolization, swollen, reactive astrocytes (pink cytoplasm in Panel A, hematoxylin and eosin), microglia and lipid macrophages (transformed microglia). Large pleomorphic nuclei of some astrocytes are clearly evidenced. Immunohistochemical staining for myelin basic protein (Panel B, immunoperoxidase (brown)) shows loss of myelin in the white matter lesion. Pleomorphic cells are immunopositive for astrocyte marker glial fibrillary acidic protein (Panel C, immunoperoxidase for GFAP). In-situ-hybridization of the demyelinated lesion (Panel D, original magnification ×400) shows enlarged irregular nuclei positive for JC virus.