New U.S. guidelines for the neuropathologic assessment of Alzheimer’s disease (AD) and related conditions are getting close to being finalized. A committee set up by the National Institute on Aging (NIA) and the Alzheimer’s Association (AA) drafted recommendations that no longer require a prior diagnosis of dementia for a postmortem assessment of AD. This would bring neuropathology in line with the diagnostic guidelines for AD published in April of this year (see ARF related news story and ARF Webinar). “The clinical guidelines now say that you can make a diagnosis of Alzheimer’s before the dementia stage, but the neuropathological criteria said that you had to have a diagnosis of dementia to make an assessment. So we were just tripping over words,” said Thomas Montine at the University of Washington in Seattle, who co-chaired the NIA-AA committee together with Bradley Hyman of Massachusetts General Hospital in Boston. “The new guidelines we are proposing recognize the reality that the disease process starts before dementia. They also acknowledge that there are other disease processes that commonly co-occur with Alzheimer’s,” Montine said.

The neuropathologic guidelines will be subject to approval at a meeting of the Alzheimer’s Disease Research Centers (ADRCs) to be held 23-24 September 2011 in San Diego, California. They will consist of a revised version of a draft document discussed at the Alzheimer's Association International Conference (AAIC) held this past July in Paris, France, where the issue was first presented and the AD community was invited to comment. The public comment period closed on 1 September 2011. Following the upcoming presentation at the ADRC meeting, the guidelines may be further revised and then submitted for publication, according to Creighton (Tony) Phelps, director of the ADRC program at the NIA. “We want to make sure that there are no lingering doubts, and achieve consensus,” he said. “We want to hear any criticism now rather than after the guidelines are published.” So far, they received 47 written comments on their draft document. “The feedback has been mostly positive, but we had some substantive criticisms that we took to heart and revised the document accordingly,” said Montine. In addition, leading neuropathologists of the BrainNet Europe (BNE) consortium last week considered the NIA-AA draft guidelines. Although BNE did not provide feedback to the NIA-AA committee during the open comment period, they now share their joint perspective, as well as their experience over the past years with assessing how to achieve agreement among neuropathologists at different sites (see BNE comment below). The NIA-AA committee, which comprises 15 members—14 based in the U.S. and one in France—started its deliberations in the fall of 2010.

Disentangling Clinical Diagnosis and Pathology
The biggest change with the new guidelines—the separation of the disease’s clinical and pathological aspects—is by all accounts being viewed as a welcome revision by AD researchers and clinicians. The earlier neuropathological criteria published in 1997, referred to as the NIA-Reagan criteria, required a history of dementia for the neuropathologic examination to occur. Those results were then used to determine whether the person’s dementia was due to AD or some other cause. The new guidelines enable the pathologist to describe all the changes in the deceased person’s brain according to a set of specified measurements, regardless of whether the person had cognitive symptoms. This approach is new to the AD field, but many other conditions already uphold this same distinction between pathology and disease. For example, many men have age-related prostate alterations, but only a small percentage will develop symptomatic prostate cancer. In essence, a common disease process causes detectable lesions in more people than those who have clinical symptoms at the time of death.

The new neuropathologic guidelines base the assessment of AD-related changes on measurements of amyloid-β (Aβ) load, the number and types of amyloid plaques, and the number of neurofibrillary tangles and their locations. “We have given a lot of attention to pathology,” said Montine. “The new guidelines are more prescriptive in what to measure than the earlier ones. We describe what to evaluate in much more detail.” The procedures were based on a literature review and the analysis of the National Alzheimer's Coordinating Center (NACC) database, a large compilation of clinical and pathological assessment data taken of each patient who comes into the memory clinics of the ADRCs across the country (see ARF interview with Bud Kukull, head of the NACC). The new guidelines also provide criteria for the assessment of other conditions that can give rise to dementia in the elderly, such as dementia with Lewy bodies (DLB, aka LBD), frontotemporal lobe dementia, vascular dementia, and dementia related to Parkinson’s disease (aka PDD).

The NIA-AA guidelines recommend that genetic risk markers and biomarkers be used in research settings to complement the neuropathologic data for the postmortem evaluation of AD. Recently, biomarker studies have taken to comparing the diagnostic value of the biomarker at hand to that of the clinical diagnosis and the postmortem pathologic assessment. This research has, in some cases, begun to question the decades-old status of postmortem neuropathology as the bona fide diagnostic gold standard for AD. But for now, the pathological assessment remains the gold standard with the new NIA-AA guidelines. “In the future it may very well be that biomarkers will be used as surrogates for neuropathologic changes, but we are not there yet,” said Phelps.

Learn Your ABCs
The 1997 guidelines relied on two sets of criteria for measuring amyloid plaques and tangles. The first set, established by the Consortium to Establish a Registry for Alzheimer's Disease (CERAD), consists of a semi-quantitative assessment of neocortical neuritic plaques, a class of amyloid plaques made up primarily of Aβ deposits surrounded by dystrophic neurites (Mirra et al., 1991). The second set of criteria rely on a staging system for neurofibrillary tangles developed by Heiko and Eva Braak, which describes six stages of AD neuropathology based on where the neurofibrillary changes occur in the brain (Braak and Braak, 1991; see also online Seminar by Braak). The combined CERAD and Braak scores provide a measure for the likelihood that a patient’s dementia was due to AD. For example, that likelihood would be “high” if the CERAD score was “frequent” and Braak stage V, but it would be “low” with a CERAD “infrequent” score and Braak stage I or II.

At the 2011 AAIC presentation, Hyman explained that the committee applied the 1997 criteria to the NACC database and found that the criteria worked well in predicting the cognitive status of people at either end of the spectrum. In other words, people whose brains were full of pathology usually had a dementia diagnosis and those with no pathology tended to be relatively cognitively normal. People whose brains had intermediate pathology according to the 1997 criteria had a 50-50 chance of having dementia. But the problem was that there were few people with substantial pathologic change and no prior diagnosis of dementia, whereas there were some people with little neuropathologic change and dementia. The 1997 criteria could not capture these cases, which are dubbed to be "off-the-diagonal."

The new guidelines address this limitation. The proposed recommendations would measure three characteristics through what is referred to as an ABC protocol:

  • A is for Aβ deposits, as measured according to the phases of deposition published by the German pathologist Dietmar Thal and colleagues (Thal et al., 2002).
  • B is for the Braak and Braak neurofibrillary tangles staining protocol.
  • C is for the CERAD scoring system.

Putting together the three scores gives a probability that the observed neuropathologic changes are related to AD. So, for example, a patient who has neocortical and hippocampal Aβ deposits (score A2), Braak stage I or II (score B1) and a CERAD score "sparse" (score C1) has a low level of AD-related neuropathology. Someone with neocortical, hippocampal, and neostriatal Aβ (score A3), Braak stage III or IV (score B2) and a CERAD score of "frequent" (score C3) would have an intermediate level of AD-related pathology.

The guidelines stipulate which brain regions to examine and what to look for. They suggest techniques for detecting pathology (i.e., staining with a stain coupled to antibodies against Aβ or tau versus a non-specific stain such as thioflavin S or silver), but they do not go as far as prescribing any particular method. “We did not feel there was a consensus on the best methodology to use,” said Montine.

That contrasts with the experience of the BrainNet Europe Consortium, according to Irina Alafuzoff at Uppsala University in Sweden. “Silver staining gives poor results. If different labs use it, they will get very different measurements. It has so many pitfalls that we decided we should not use it within BrainNet,” she said. “Counting lesions also gives very different results [from lab to lab].” Several studies conducted in the last four years (Alafuzoff et al., 2008; Alafuzoff et al., 2008; Alafuzoff et al., 2009; Alafuzoff et al., 2009) have shown that by using immunohistochemistry for Aβ and tau to measure amyloid and NFT load, the consortium members could achieve 80 percent agreement in their pathological assessments of autopsy samples from the same brain. BrainNet Europe neuropathologists are now preparing to publish their own recommendations based on these findings. However, Alafuzoff is concerned that “the U.S. and Europe will now be following different guidelines and it will be difficult to compare results.”

Montine pointed out that, unlike BrainNet, which is a research consortium, the NIA-AA guidelines are meant to assist both neuropathologists working in a clinical setting and those working in research settings. He acknowledged that having consistent methods is important in a research setting when you need to stringently compare results, but it is less critical when using the assessment to make a clinical diagnosis. It would be difficult for many clinics to conduct studies using more expensive antibody-based stains. “We wanted to be both scientifically rigorous but practically useful to people,” he said.

This issue is but one of many aspects of the guidelines that were openly debated at the 2011 AICC conference. Part 2 of this series summarizes highlights of that discussion.—Laura Bonetta.

This is Part 1 of a two-part series. See also Part 2.

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  1. Comment on the Consensus Recommendations for the Postmortem Neuropathological Assessment of Alzheimer’s Disease

    Irina Alafuzoff (1), Thomas Arzberger (2), Penelope Korkolopoulou (3), Orso Bugiani (4), Charles Duyckaerts (5), Isidro Ferrer (6), Ellen Gelpi (7), Steve Gentleman (8), Giorgio Giaccone (4), Manuel B Graeber (9), Tibor Hortobagyi (10), James W Ironside (11), Kurt Jellinger (12), Gabor G Kovacs (20), David Meyronet (13), Camelia-Maria Monoranu (14), Piero Parchi (15), Tamas Revesz (16), Annemieke Rozemuller (17), Walter J Schulz-Schaeffer (18), Danielle Seilhean (5), Nathalie Streichenberger (13), Fabrizio Tagliavini (4), Dietmar Thal (19), Hans A Kretzschmar (2).

    See author affiliations below

    Two significant changes characterize the recently revised recommendations of the National Institute on Aging-Alzheimer’s Association (NIA-AA) for the diagnosis of Alzheimer’s disease (AD).

    First, the NIA-AA panel of 2011 agreed to disentangle the clinicopathological and neuropathological terms applied in the diagnosis of AD. Based on the consensus, the term AD should refer to clinical signs, symptoms, and behavioral changes in a clinical continuum including preclinical, mild cognitive impairment, and dementia in a patient with AD-related pathology. The term “AD neuropathological changes” should refer to the presence and extent of pathology, regardless of the clinical setting.

    Second, the panel has emphasized the importance of the assessment of other pathologies commonly seen in aged subjects and particularly in association with AD neuropathological changes.

    The BrainNet Europe Consortium (BNE) fully agrees with this approach, and recommends the assessment of AD-related pathology in aged subjects regardless of the clinical setting. Furthermore, the recommendation to assess and acknowledge the concomitant pathological alterations seen in a subject is a welcome change.

    The NIA-AA panel has also delivered recommendations regarding the brain regions and type of lesions to be assessed, the latter including AD-related pathology, Lewy body disease (LBD)-related pathology, cerebrovascular alterations, and hippocampal sclerosis.

    Regarding AD neuropathological changes, it is recommended to assess the severity of β amyloid (Aβ) deposits based on the phase assessment described by Thal and coworkers in 2002, neurofibrillary tangles (NFT) based on staging of NFT pathology as described by Braak and Braak in 1991, and neuritic plaques (NP) based on the semi-quantitative scoring system described by Mirra and colleagues in 1991 (CERAD). This is recommended to be carried out to reach an “ABC score” identifying those with high, intermediate, and low level of AD neuropathological changes. Regarding LBD, it is recommended to assess α-synuclein (αS) pathology and classify this pathology following McKeith and colleagues’ criteria from 2005. Recommendations regarding extent of vascular pathology and hippocampal sclerosis are descriptive.

    BNE fully supports this detailed assessment of various pathologies. There is, however, a significant pitfall that should be taken into account, particularly if the goal is to recommend these criteria to a broad number of assessors having variable expertise (neuropathologists with various subspecialties as well as general pathologists). Our long-lasting experience in assessing inter-rater agreement among a high number of European neuropathologists has repeatedly shown that the agreement rate is significantly influenced by the level of experience of both the assessors and the technical personnel carrying out the stains.

    The trials carried out by BNE highlighted the significant inter-laboratory variability of special stains such as silver stains as well as the relatively low agreement among assessors in the identification of certain lesions (neuritic vs. diffuse plaques) and the assessment of extent of pathology, i.e., counts of defined lesions. It was also noted that not only special stains such as silver, but also immunohistochemical stains, yielded poor agreement in the semi-quantitative assessment of lesions. Thus, BNE concluded that in order to reach a high agreement among a significant number of assessors, the emphasis should be on well-defined neuroanatomical regions to be assessed, on secure visualization of hallmark pathology to be assessed, and on a simple reproducible dichotomized strategy to assess the visualized lesions avoiding semi-quantitative evaluations.

    Currently, one of the most reproducible strategies to demonstrate AD and LBD pathology is immunohistochemistry, due to its molecular character and the widespread use of automatic staining machines. Furthermore, the dichotomized assessment of AD and LBD pathological alterations has the capacity to yield a high agreement. Thus, up to 30 BNE assessors reached high agreement rates while assessing immunohistochemically labeled hyperphosphorylated immunoreactive (IR) neuropil threads, Aβ-IR aggregates, and αS-IR inclusions/neurites. BNE recommendations should guarantee a high rate of agreement among a large number of assessors, even if the assessments are carried out by less trained or experienced colleagues, e.g., a general pathologist in charge of the autopsy service.

    The BNE consortium evaluated the agreement rates following current assessment strategies, including those recommended by NIA-AA. These assessments were, however, always based on immunohistochemically stained sections, as the silver stains yielded poor agreement rates. BNE is thus concerned that, due to the methodological pitfalls regarding silver staining, the semi-quantitative assessment of neuritic plaques might cause more problems than anticipated.

    Another issue that should be considered in this context is the stepwise pattern of assessment of AD and LBD pathological lesions. Financial support for neuropathological assessment varies from center to center. The production of 13 paraffin blocks from each autopsy case, demented or aged unimpaired, and the staining of each section with a routine stain such as haematoxylin-eosin should be feasible in most laboratories. However, to carry out routinely all the special and immunohistochemical stains suggested for the investigation of AD and LBD pathology on each block might prove too costly. Based on the above, a stepwise approach would be more affordable and is especially recommended, also keeping in mind that the number of proteins and concomitant pathologies to be assessed in neurodegenerative diseases is likely to continue to increase with time. Thus, in each case, in addition to haematoxylin-eosin stain on each block, six immunohistochemical stains should be carried out initially (Aβ, in the occipital cortex, HPtau and pTDP-43 in the hippocampus, and α-synuclein in the medulla, midbrain, and amygdala). If immunoreactivity is noted for a given protein, staining of additional brain regions should be carried out to stage the pathology. (Table available upon request.) 

    1. Uppsala University, Department of Genetics and Pathology, Rudbeck Laboratory and Uppsala University Hospital, Department of Pathology and Cytology 751 85 Uppsala, Sweden
    2. Institut fur Neuropathologie, LMU Munchen, Germany
    3. Department of Pathology, National and Capodistrian University, Athens, Greece
    4. Fondazione IRCCS Istituto Neurologico Carlo Besta, Milano, Italy
    5. Laboratoire de Neuropathology Escourolle, Hopital de la Salpetriere, Paris, France
    6. Institut de Neuropatologia, Hospital Universitari de Bellvitge, Universitat de Barcelona, Barcelona, Spain
    7. Neurological Tissue Bank, Biobanc-Hospital Clinic-IDIBAPS, Barcelona, Spain
    8. Neuropathology Unit, Department of Medicine, Imperial College London, UK
    9. The Brain and Mind Research Institute, Faculty of Medicine and Faculty of Health Sciences, The University of Sydney, Australia
    10. Department of Clinical Neuroscience, Institute of Psychiatry, King’s College, London, UK, and Institute of Pathology, University of Debrecen, Hungary
    11. National CJD Research & Surveillance Unit, School of Medicine and Clinical Medicine, University of Edinburgh, Western General Hospital, Edinburgh, United Kingdom
    12. Institute of Clinical Neurobiology, Vienna, Austria
    13. Neuroscience Center, University Lyon, Hospices Civils de Lyon, Centre de Pathologie et de Neuropathology, Est Lyon, France
    14. Department of Neuropathology, Institute of Pathology, University of Wuerzburg, Germany
    15. Dipartemento di Scienze Neurologiche, Universita di Bologna, Bologna, Italy
    16. Department of Molecular Neuroscience, UCL Institute of Neurology, University College London, London, UK
    17. Department of Pathology, VU University Medical Centre Amsterdam, The Netherlands
    18. University Medical Centre Goettingen, Department of Neuropathology Goettingen, Germany
    19. Laboratory of Neuropathology, Institute of Pathology, University of Ulm, Ulm, Germany
    20. Institute of Neurology, Medical University of Vienna, Austria

    References:

    . Interlaboratory comparison of assessments of Alzheimer disease-related lesions: a study of the BrainNet Europe Consortium. J Neuropathol Exp Neurol. 2006 Aug;65(8):740-57. PubMed.

    . Staging of Alzheimer disease-associated neurofibrillary pathology using paraffin sections and immunocytochemistry. Acta Neuropathol. 2006 Oct;112(4):389-404. PubMed.

    . Assessment of alpha-synuclein pathology: a study of the BrainNet Europe Consortium. J Neuropathol Exp Neurol. 2008 Feb;67(2):125-43. PubMed.

    . Staging of neurofibrillary pathology in Alzheimer's disease: a study of the BrainNet Europe Consortium. Brain Pathol. 2008 Oct;18(4):484-96. PubMed.

    . Inter-laboratory comparison of neuropathological assessments of beta-amyloid protein: a study of the BrainNet Europe consortium. Acta Neuropathol. 2008 May;115(5):533-46. PubMed.

    . Assessment of beta-amyloid deposits in human brain: a study of the BrainNet Europe Consortium. Acta Neuropathol. 2009 Mar;117(3):309-20. PubMed.

References

Webinar Citations

  1. Two New Sets of Diagnostic Criteria—Which Is Right for Your Clinic?

News Citations

  1. Tom Fagan Interviews Bud Kukull
  2. Draft Guidelines Spark Discussion, Highlight Unknowns in Field

Paper Citations

  1. . The Consortium to Establish a Registry for Alzheimer's Disease (CERAD). Part II. Standardization of the neuropathologic assessment of Alzheimer's disease. Neurology. 1991 Apr;41(4):479-86. PubMed.
  2. . Neuropathological stageing of Alzheimer-related changes. Acta Neuropathol. 1991;82(4):239-59. PubMed.
  3. . Phases of A beta-deposition in the human brain and its relevance for the development of AD. Neurology. 2002 Jun 25;58(12):1791-800. PubMed.
  4. . Staging of neurofibrillary pathology in Alzheimer's disease: a study of the BrainNet Europe Consortium. Brain Pathol. 2008 Oct;18(4):484-96. PubMed.
  5. . Inter-laboratory comparison of neuropathological assessments of beta-amyloid protein: a study of the BrainNet Europe consortium. Acta Neuropathol. 2008 May;115(5):533-46. PubMed.
  6. . Assessment of beta-amyloid deposits in human brain: a study of the BrainNet Europe Consortium. Acta Neuropathol. 2009 Mar;117(3):309-20. PubMed.
  7. . Staging/typing of Lewy body related alpha-synuclein pathology: a study of the BrainNet Europe Consortium. Acta Neuropathol. 2009 Jun;117(6):635-52. PubMed.

Other Citations

  1. ARF related news story

External Citations

  1. Alzheimer’s Disease Research Centers
  2. draft document
  3. National Alzheimer's Coordinating Center
  4. Consortium to Establish a Registry for Alzheimer's Disease

Further Reading