Diagnosis of progressive multifocal leukoencephalopathy by brain biopsy with biotin labeled DNA:DNA in situ hybridization.

DNA:DNA in situ hybridization using a cloned JC virus (JCV) DNA probe labeled with biotin confirmed the presence of JCV DNA in formalin-fixed, paraffin-embedded brain biopsies from four cases of progressive multifocal leukoencephalopathy (PML). Only small pieces of tissue were available in each case. Detection of the JC DNA:DNA hybrids was carried out by affinity cytochemistry. JCV DNA was identified predominantly in the nuclei of interfascicular oligodendrocytes in demyelinated areas of the biopsies. JC virus was isolated from one case, and the diagnosis of PML was substantiated in all cases by electron microscopic identification or immunocytochemical labeling of JC viral antigen. In situ hybridization using a biotin labeled JCV DNA probe is a specific, sensitive and convenient method for confirming the diagnosis of PML in suspected cases evaluated by brain biopsy.