Section 3 -

Surgical Pathology of Prion diseases and other neurodegenerative diseases Dr. Gerard H. Jansen Department of Pathology and Laboratory Medicine The Ottawa Hospital Ottawa , Canada

Prion diseases and the classic diseases of neurodegeneration are currently not curable, and only in part accessible to symptomatic therapy. Therefore, from a therapeutic viewpoint, the surgical pathology of these diseases is of limited importance. They are however much more important in the field of autopsy pathology, and, especially in prion diseases, in patient management, infection control and public health. However from the patient's perspective it can be very important to exclude some of the more therapy accessible diseases that mimic these dementias. Although public health and infection management issues can in general not justify the need to do a brain biopsy alone, in countries where autopsies are not considered to be a reasonable means of diagnosis, it is understandable that biopsies are more easily taken for combined diagnostic, management and public health reasons. Prion diseases Prion diseases can be separated into those occurring sporadically (sporadic Creutzfeldt-Jakob disease), those acquired through infection (iatrogenic CJD, variant CJD, and Kuru), and genetically transmitted prion diseases (familial CJD, Gerstmann-Sträussler-Scheinker disease, and Familial Fatal Insomnia). While globally sporadic CJD is most important in frequency (85%), and infection acquired prion disease is least prevalent (around 1%), regional variation exists. Per example in the United Kingdom the frequency of variant CJD has been on average 17% of all CJD cases since 1995, and Kuru has been historically the most prevalent prion disease in Papua New Guinea . The morphology of almost all prion diseases is primarily that of spongiosis, combined with neuronal loss, and in more severely affected areas also gliosis, in the grey matter of the brain. By immunohistochemistry the deposition of the abnormal, protease resistant, prion protein can be shown using a variety of commercially available antibodies. In variant CJD the florid-plaque is the tell-tale sign of the disease and in GSS multi-centric plaques are characteristic. However there are subtle differences in all prion diseases on close comparison, and even within the group of sporadic CJD there is a range of subtle differences in clinical and pathological presentation. These differences are related to the patient's own prion protein genotype and the glycosylation state of the prion protein. In these subtypes of sporadic CJD there is variation in the regional distribution of abnormalities, the size of vacuoles (small or large confluent vacuoles), and the presence of plaques (most notably the 'Kuru'-plaques that are present in the 'MV2' variant of sporadic CJD). The combination of histology and immunohistochemistry is mostly enough to establish the definite diagnosis of prion disease, and to identify variant CJD and GSS. However to successfully identify genetic prion diseases, genetic analysis is essential (on blood or frozen brain tissue). Further Western blotting for protease resistant prion protein can be performed on frozen tissue. While the latter is not a required diagnostic tool, it can be extremely helpful in difficult cases. It is therefore that in brain biopsies for suspected CJD a generous biopsy should be taken (here the old rule of 1cm3 is still relevant), where half of the biopsy should be frozen. As there is regional variance of pathology it is possible that only very limited pathology is present. Also in these cases Western blotting can be extremely helpful. For genetic forms of prion diseases and when iatrogenic CJD are considered, a good targeted history is also important. Often at this stage of the disease it is the relatives of the patient who will provide most of the information. While false negative biopsies can be possible, also an occasional false positive is known to occur. This is mostly due to over-calling spongiosis present as typical for CJD, or alternatively due to overstained prion protein immunohistochemistry. Very mild spongiosis can be found also in most neurodegenerative diseases (mostly in higher cortical layers, while in prion diseases this occurs in either the lower or in all cortical layers), in hypoxia, oedema, irradiation, and for instance in hepatic encephalopathy (in the latter two it is frequently seen in the lower cortical layers and upper white matter). Without pathological analysis the patients can be classified according to WHO clinical criteria as probable or possible CJD, when they meet certain criteria, but only probable and definite CJD cases are generally considered to actually 'have' CJD from a surveillance point of view. In variant CJD, prion protein deposition can also be shown in tonsil biopsies by immunohistochemistry and in other lymphoid tissue. There is however no specific change seen in the routine stains in lymphoid organs. Other diseases of neurodegeneration The diagnosis of the classical diseases of neurodegeneration has changed over the past two decades with the discovery of the proteins that accumulate in neurons, glial cells and the interstitium. These diseases are separated into Alzheimer's disease (beta amyloid positive interstitial plaques, tau positive neurofibrillary tangles), Tauopathies (phosphorylated tau positive swollen neurons in Pick's disease and in Cortico-Basal degeneration, grain positivity in tau stains in Argyrophilic Grain disease, filamentous tau inclusions in neurons of familial frontotemporal dementia), and into the synucleopathies (Dementia with Lewy bodies: α-synuclein positivity in intracytoplasmic neuronal inclusion of cortical Lewy-body type). It is important to realize that all of these diseases now have specific criteria for their diagnsosis by histopathology. As such it requires autopsy to sample all the regions that one needs to examine to satisfy these criteria. Therefore one can only suggest a diagnosis on a biopsy, and has to leave the possibility open of a case not matching the criteria, or the possibility of an alternative diagnosis. Combined diagnoses between these diseases (for instance Alzheimer's disease combined with Lewy body dementia) and between these diseases and prion diseases (Alzheimer's disease combined with sporadic CJD) are known to occur occasionally. Differential diagnosis The most important differential diagnoses are those diseases that may present with dementia and that are potentially treatable. Most notably infections such as dementia paralytica (syphilis), cerebral Whipple's disease, cerebral tuberculosis, general viral infections, herpes simplex virus, and AIDS dementia are important here. Neoplastic: mass lesions such as metastases, infiltrating gliomas and primary CNS lymphomas, and the rare angiotropic (intravascular) lymphoma. Vascular diseases: vascular dementia, Burger's disease, CADASIL, and multiple strokes in mitochondrial disease. While there are alternative diagnostic tools to investigate these diseases, they should be considered when reviewing a biopsy. Also the autoimmune disorders such as primary CNS angiitis, giant cell arteritis, SLE, Sarcoid, Sjögren's disease are important as they may be treated by anti-inflammatory means. The differential diagnosis of paraneoplastic CNS encephalitis is not frequently diagnosed by biopsy, and rarely therapeutically approachable in the stage where dementia is present. Infection control and laboratory management in prion diseases In most cases where CJD is reasonably expected from the clinical history and neurological examination, infection preventative measures are to be taken when undertaking a brain biopsy according to local and or national guidelines, in order to prevent infection of patients who subsequently have surgery, but also to prevent occupational hazards (or in case of suspected variant CJD, at any type of surgery). At a surgical level this will mostly mean use of dedicated surgical equipment, which will be quarantined until the results of the biopsy are known. After that a decision on destruction or sterilization of the instruments must be made. At a laboratory level one can expect the surgeon to inform the laboratory of a suspected case so that appropriate measures can be taken in the processing of the tissue. When a diagnosis of CJD is reasonably expected in a case brain biopsies are considered to be material to be processed in a laboratory capable of handling biosafety hazard level 3, in most countries. There is quite some diversity in the regional/national rules and regulations attached to working with these materials in these laboratory surroundings. An escape from this level 3 classification can be to consider the tissue to be 'diagnostic tissue', for which these rules do not apply. Mostly however this 'diagnostic' classification means that there is a low level of suspicion of the agent actually being present. Luckily in many countries with an active CJD surveillance, designated CJD laboratories have been set up. Also on the bright side is that no epidemiological evidence as yet has been found linking a higher risk of acquiring CJD to working in a neuropathology/pathology lab, despite incidental cases of CJD being reported in these groups of health care workers in literature over the past 40 years. As decontamination for tissue blocks after fixation, formic acid 96% (at least) treatment for 1 hr, followed by generous rinsing with formalin, is used. While immunohistochemistry results are not changed by formic acid, several more conventional stains are problematic after this treatment (Congo red, silver stains). A pathologist can be expected to notify the surgeon of the result of the biopsy so that adequate measures can be taken with respect to the quarantined instruments. Also when a diagnosis of CJD is made unexpectedly on a surgical biopsy the pathologist should inform the surgeon as soon as possible, in order to take surgical equipment out of circulation, that was used in this surgery. Given the difficult decontamination in CJD there is no place for frozen section diagnosis in cases reasonably suspected to be CJD. Further reading Diagnostic aspects CJD clinical: http://www.who.int/entity/bloodproducts/TSE-manual2003.pdf annex 1, page 71-72 CJD histopathology: Budka H, Aguzzi A, Brown P, Brucher JM, Bugiani O, Gullotta F, Haltia M, Hauw JJ, Ironside JW, Jellinger K, et al.: Neuropathological diagnostic criteria for Creutzfeldt-Jakob disease (CJD) and other human spongiform encephalopathies (prion diseases).Brain Pathol. 1995 Oct;5(4):459-66. Variant CJD: Ironside JW, Head MW, Bell JE, McCardle L, Will RG: Laboratory diagnosis of variant Creutzfeldt-Jakob disease. Histopathology. 2000 Jul;37(1):1-9. http://whqlibdoc.who.int/hq/2002/WHO_CDS_CSR_EPH_2001.5.pdf Annex 5 , page 20 Other neurodegenerations: Esiri M, Lee VMY, Trojanowski JQ (Eds): The Neuropathology of dementia. Cambridge University Press, Cambridge, 2004. ISBN 0521 81915 6 Infection control Canadian infection control guidelines for CJD: http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/02pdf/28s5e.pdf British infection control guidelines: http://www.advisorybodies.doh.gov.uk/acdp/tseguidance/index.htm WHO guidelines on tissue infectivity in prion diseases: http://www.who.int/bloodproducts/tse/WHO TSE Guidelines FINAL-22 JuneupdatedNL.pdf EUROCJD & NEUROCJD collaborating countries: http://www.eurocjd.ed.ac.uk Autopsies: Bell JE, Ironside JW: How to tackle a possible Creutzfeld-Jakob disease necropsy. J Clin Pathol. 1993;46:193-197.