Progressive multifocal leukoencephalopathy. Diagnosis by in situ hybridization with a biotinylated JC virus DNA probe using an automated Histomatic Code-On slide stainer.

The accurate surgical pathological diagnosis of progressive multifocal leukoencephalopathy (PML) depends on the demonstration of pathognomonic histological features in cerebral biopsy tissue. The diagnosis may be difficult, however, if only small tissue fragments are submitted from the center of a demyelinating lesion. Previous studies by other authors have established that in situ hybridization with a biotinylated JC virus DNA probe can be a valuable diagnostic adjunct because it identifies the virally infected cells with great specificity and does not depend on the larger specimen, which may be necessary for a firm histological diagnosis. To confirm and extend these findings, we have used a commercially available biotinylated JC virus DNA probe to demonstrate the presence of viral DNA in formalin-fixed, paraffin-embedded tissues from four open biopsies, four needle biopsies, and two autopsies of patients with PML. With the goal of making this procedure applicable to the general surgical pathology laboratory, this method was adapted to the Histomatic Code-On slide stainer. The Histomatic is a programmable, robotic instrument with walk-away capability for hybridization histochemistry. Operation of this instrument requires the same expertise as execution of immunocytochemistry. With the advent of commercially available JC virus DNA probes and an automated system for hybridization histochemistry, this technology for diagnosis of PML may enter the routine diagnostic surgical pathology laboratory.