This is Alzheimer's disease, with numerous senile plaques and also amyloid angiopathy (at the lower right with the thioflavin stain), as seen with a thioflavin fluorescent stain and a polarized Congo red stain shown above for comparison. Note that thioflavin (staining with either thioflavin S or T will appear similarly) stains more of the plaque than the Congo red, which typically highlights the central core of the plaque. The pathognomonic microscopic feature of AD is an increased number of neuritic plaques in the cerebral cortex. These neuritic plaques are composed of tortuous neuritic processes surrounding a central amyloid core. Reactive astrocytes and microglia may appear at the periphery of these plaques. Though plaques may easily be found in the hippocampus, their presence in increased numbers in neocortex is necessary for a diagnosis of AD. The amyloid core consists primarily of a small peptide known as Aß which is derived from the larger amyloid precursor protein (APP). Plaques that have the amyloid proteins but lack the neuritic processes are known as diffuse plaques, which do not count toward the diagnosis of AD. Since the number of plaques increases with age, the number needed for diagnosis of AD is age-dependent. Many AD patients also have cerebral amyloid angiopathy (CAA), which is promoted via the presence of an abnormal apolipoprotein E (apoE) epsilon4 allele, though significant hemorrhage from CAA is less frequent.
There were 11 responses correctly identifying the stain and 60 correctly identifying Alzheimer's disease out of 102 total entries for case 46.
| Our winner is: Kathia E. Rosado, MD of Atlanta, Georgia, USA
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