A non-toxic method for the demonstration of gliosis

Neuropathology laboratories have traditionally relied upon the Holzer method for demonstration of gliosis. However, concerns about the toxicity of aniline oil have markedly reduced the application of this method in recent times. Immunostains for glial fibrillary acidic protein (GFAP) are excellent for showing gliosis in grey matter but cannot distinguish normal from abnormal astrocytes in the white matter. The traditional phosphotungstic acid hematoxylin (PTAH) method stains myelin as well as glial fibers and, thus, is not useful for recognizing areas of gliosis. Here we present a method for the routine demonstration of gliosis based on a modification of Mallory's PTAH method. The staining of myelin is eliminated by increasing the concentration of potassium permanganate to 5% (from 0.25-1% in traditional methods). The use of aminoalkylsilane adhesive ensures that the sections do not detach during the procedure. Areas of gliosis stand out against a pale background because only abnormal astrocytes and their processes are stained, both in grey and white matter. The method minimizes the use of toxic chemicals and can be completed within an eight hour work day in any routine neurohistology laboratory, using formalin fixed, paraffin-embedded tissue.