Two types of dystrophic neurites in senile plaques of Alzheimer disease and elderly non-demented cases.

Senile plaques (SPs) occur profusely in brain tissue of Alzheimer disease (AD) cases, and sparsely in brain tissue of elderly normals. Two types of dystrophic neurites (DNs) have been identified in SPs. Type 1 are the classically described elongated forms. Type 2 are globular in shape. Type 1 DNs are stained immunohistochemically by antibodies to A68 protein, other forms of phosphorylated tau, and N-terminal epitopes of amyloid precursor protein (APP), as well as an antibody which preferentially recognized conjugated ubiquitin. Type 2 DNs are stained immunohistochemically by antibodies to chromogranin A and C-terminal epitopes of APP, as well as an antibody which preferentially recognizes free ubiquitin. SPs of AD cases usually contain a mixture of type 1 and type 2 DNs. However, in the neocortex of elderly normals, which have few neurofibrillary tangles and neuropil threads, the DNs in the SPs are restricted to type 2. These data suggest that SPs containing only type 2 DNs may be benign, and independent of neurofibrillary pathology.