a degenerative organic mental disease characterised by progressive brain deterioration and dementia. The disease was originally described as dementia, presenile occurring in persons under the age of 65 (as opposed to dementia, senile with onset at or after 65); however, onset may occur at any age. There is no pathophysiological nor clinical distinction between the two stages of onset of alzheimers. Women appear to be affected twice as frequently as men. It is characterised pathologically by the triad of senile plaques, neurofibrillary tangles, and neuropil threads.