Two distinct types of intraneuronal neurofibrillary tangles highlighted by polarized light after silver impregnation with a modified Bielschowsky method

Neurofibrillary tangles (NFTs) are one of the morphological hallmarks of Alzheimer's disease. The birefringency and dichroism of NFTs following congo red staining have long been known. Herein, we report the observation that a subset of NFTs show distinct birefringency induced by a modified Bielschowsky silver impregnation method. Birefringency of NFTs could not be elicited after silver impregnation with one other version of the Bielschowsky method or with the Bodian technique. To our knowledge, these properties of NFTs after metal impregnation have not been previously documented.