Senile plaques

Senile plaques (also known as neuritic plaques) are extracellular deposits of amyloid beta in the grey matter of the brain.Degenerative neural structures and an abundance of microglia and astrocytes can be associated with senile plaque deposits. These deposits can also be a byproduct of senescence (ageing). However, large numbers of senile plaques and neurofibrillary tangles are characteristic features of Alzheimer's disease. Abnormal neurites in senile plaques are composed primarily of paired helical filaments, a component of neurofibrillary tangles. The plaques are variable in shape and size, but are on average 50 µm in size. In Alzheimer's disease they are primarily composed of amyloid beta peptides. These polypeptides tend to aggregate and are believed to be neurotoxic.

In 1892 Paul Blocq and Gheorghe Marinescu first described the presence of plaque deposits in grey matter. As a result of their similarity to actinomyces druses, they were called druse necrosis by Oskar Fischer during the early 20th century. The connection between plaques and dementia was discovered by Alois Alzheimer in 1906. By 1911 Max Bielschowsky proposed the amyloid-nature of plaque deposits. The same year Teofil Simchowicz introduced the term senile plaques. Wisniewski coined the term neuritic plaques in 1973. The second half of the 20th century saw proposed theories of immunological and genetic factors in plaque formation. Statistical investigations were performed by J.A.N. Corsellis and M. Franke in the 1970s. M. Franke showed that a demential disease is likely to occur when the number of senile plaques in the frontal cortex is more than 200/mm³. By 1985 beta amyloid formations were successfully identified through biochemical techniques, though many unsolved questions about the importance and formation of senile plaques remained.

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