Table 3. “ABC” Score for Level of AD Neuropathologic Change.
AD neuropathologic change is evaluated with an “ABC” score (Table 2): Aβ/amyloid plaques (A), NFT stage (B), and neuritic plaque score (C). The combination of A, B, and C scores is designated as “Not”, “Low”, Intermediate” or “High” AD neuropathologic change. “Intermediate” or “High” AD neuropathologic change (black background) is considered sufficient explanation for dementia.
| AD Neuropathologic Change | B1 | |||
|---|---|---|---|---|
| A2 | C3 | 0 or 1 | 2 | 3 |
| 0 | 0 | Not4 | Not4 | Not4 |
| 1 | 0 or 1 | Low | Low | Low5 |
| 2 or 37 | Low | Intermediate | Intermediate5 | |
| 2 | Any C | Low6 | Intermediate | Intermediate5 |
| 3 | 0 or 1 | Low6 | Intermediate | Intermediate5 |
| 2 or 3 | Low6 | Intermediate | High | |
Aβ/amyloid plaque score should be determined by the method of Thal, et al. [57].
Neuritic plaque score should be determined by the method of CERAD [41].
Medial temporal lobe NFTs in the absence of significant Aβ or neuritic plaques occurs in older people and may be seen in individuals without cognitive impairment, with mild impairment, or with cognitive impairment from causes other than AD [44]. Consider other diseases when clinically or pathologically indicated.
Widespread NFTs with some Aβ/amyloid plaques but limited neuritic plaques is relatively infrequent and when it occurs, other diseases, particularly tauopathies, should be considered. Such cases may not fit easily into a specific Braak stage, which is intended for categorization of AD-type NFTs.
Higher levels of Aβ or neuritic plaques with low Braak stage should prompt consideration of contribution by co-morbidities like vascular brain injury, Lewy body disease, or hippocampal sclerosis. Also, consider additional sections as well as repeat or additional protocols to demonstrate other non-AD lesions.
High levels of neuritic plaques in setting of low Thal phase is a rare occurrence and should prompt reconsideration of neuritic vs. diffuse plaques, and the possible contribution of other diseases to cognitive impairment or dementia.