Early morphologic diagnosis of herpes simplex virus encephalitis: advantages of electron microscopy and immunoperoxidase staining.

The authors compared three morphologic techniques that can be used in the diagnosis of herpes simplex virus encephalitis. The pathologic material was derived from brain biopsy, autopsy, or both in ten culture-proven cases. On conventional light microscopic examination, typical intranuclear Cowdry type A inclusions were recorded as absent (one case), rare (six cases), or numerous (three cases). Electron microscopic evaluation, performed in nine cases, revealed intranuclear viral particles in five biopsy and two autopsy cases, including four cases in which inclusions were rare or absent on light microscopy. In one biopsy specimen, unequivocal virus particles could not be identified ultrastructurally, although they were present in subsequent autopsy material. Immunoperoxidase staining using the peroxidase-antiperoxidase (PAP) method and type-specific anti-herpes simplex type 1 antiserum, performed on paraffin-embedded tissue, demonstrated strongly positive specific immunoreactivity in all ten cases. The potential for rapid specimen preparation, the relative sensitivity of electron microscopy, and the extreme sensitivity and specificity of the PAP-immunoperoxidase method offer obvious advantages in the early morphologic diagnosis of herpes simplex virus encephalitis.