Comparison of three silver stains for demonstrating neurofibrillary tangles and neuritic plaques in brain tissue stored for long periods.

Three methods were compared to find a reliable method for demonstrating neurofibrillary tangles (NFTs) and neuritic plaques (NPs) in brain tissue stored for long periods in formalin or as paraffin blocks. The short-term fixation of tissue, e.g. up to 6 months in formalin does not usually present a problem using any of the three methods tried, e.g. Gallyas, modified Palmgren, or modified Bielschowsky, but once the time lengthens to 6 years or more the demonstration of NFTs and NPs is not so reliable using the first two methods. The modified Bielschowsky method, however, demonstrates well both NFTs and NPs in material stored in formalin or as paraffin blocks for long periods, e.g. 7 years, and also compares favourably with the other methods on freshly processed material and fixed tissue, stored for shorter periods. We also noted as a consistent trend, irrespective of the staining technique employed, the detection of fewer plaques and tangles in material stored in formalin, as opposed to that stored as blocks embeded in paraffin wax.