Variant Creutzfeldt-Jakob Disease and Bovine Spongiform Encephalopathy Workup

Updated: Jan 11, 2016
  • Author: Erik Z Krause, DO; Chief Editor: Niranjan N Singh, MD, DM  more...
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Workup

Approach Considerations

The initial workup for variant Creutzfeldt-Jakob Disease (CJD) should include tests for dementia and encephalopathy. In addition, tests should include a serum chemistry profile, liver function tests, vitamin B-12 measurement, methylmalonic acid measurement, folate value, thyroid studies, ammonia value, erythrocyte sedimentation rate, C-reactive protein value, and neurosyphilis and HIV tests when appropriate.

While no current blood test exists for the detection of variant CJD, Jackson et al. explored the possiblity of developing a prototype test that can detect disease-associated prion protein from whole blood using stainless steel powder. The group concluded that the assay's high sensitivity (71.4%) and specificity (95%) supports the need to pursue further research in this particular screening assay. [92]

Findings from routine CSF studies are unremarkable; however, studies on brain-specific proteins, such as protein 14-3-3, neuron-specific enolase (NSE), S-100b, and total tau protein (t-tau) are helpful. The detection of CSF 14-3-3 is nonspecific. (The 14-3-3 protein test is performed as a service by the Laboratory of CNS Studies, National Institute of Neurologic Disorders and Stroke [NINDS], National Institutes of Health, Bethesda, Maryland [Telephone: 301-496-4821].) These proteins are not prion specific and are considered to be general markers for neuronal injury.

CSF tau protein has the best sensitivity (80%) and specificity (94%) of any of the proteins investigated in variant CJD. CSF tau protein is an axonal microtubular phosphoprotein, and it is unclear why it has a higher sensitivity than the neuronal markers 14-3-3 and NSE. The combination of a positive CSF 14-3-3 and an increased CSF tau protein has an increased sensitivity (86%) for the detection of variant CJD, with only a slight reduction in specificity (90%). [93]

Ubiquitin has the potential of serving as a CSF marker in CJD. [94] A specific reduction in the CSF uric acid levels has been shown in variant CJD but not in sporadic CJD, which may potentially help in the differential diagnosis of variant CJD. [95, 96]

A newer test called real-time quaking-induced conversion (RT-QuIC) has been shown to have modest potential for prion detection in CSF, but is still lacking substantial data. [97] . However, RT-QuIC has been negative in all vCJD assays to date.

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Histologic Findings

Tonsil biopsy

In patients with variant Creutzfeldt-Jakob Disease (CJD), the abnormal prion protein (PrPSc) is detectable in follicular dendritic cells within germinal centers in lymphoid tissues, including the tonsils, lymph nodes, spleen, thymus, and gut-associated lymphoid tissues in the appendix and small intestine (see the image below). [47, 98] The lymphoreticular accumulation of PrPSc, as assessed by immunocytochemistry, has been shown to be a highly specific feature of variant CJD. [99]

Prion protein (PrP) accumulation in the tonsil in Prion protein (PrP) accumulation in the tonsil in variant Creutzfeldt-Jakob disease within follicular dendritic cells and macrophages in a germinal center as demonstrated by PrP immunocytochemistry. From Ironside JW, Frosch MP, Bernardino G. "Human prion diseases." In: Gray F, De Girolami U, Poirier J, eds. Escourelle & Poirier Manual of Basic Neuropathology. Philadelphia, Pa: Elsevier, 2004: 145-57.

A distinctive PrPSc subtype (4t) is consistently observed in antemortem and postmortem tonsil examinations in cases of variant CJD. [47] In variant CJD, the proportion of the prion protein glycoforms in type 4t PrPSc in the tonsils differs from that in type 4 PrPSc in brain tissue, which implies the superimposition of tissue- and strain-specific effects of prion protein glycosylation.

Tonsil biopsy has shown 100% sensitivity and specificity for the diagnosis of variant CJD and allows diagnosis of variant CJD at an early clinical stage. [98, 100] Therefore, a tonsil biopsy is an important diagnostic test for suspected variant CJD, particularly if characteristic MRI findings are absent.

Furthermore, large-scale anonymous screening of routine surgical tonsillectomy tissues may provide an early warning sign of a high-level preclinical variant CJD infection [101, 102] , although a relatively small sample of 2000 consecutive tonsillectomy specimens obtained in the United Kingdom did not detect any positive cases on analysis by both high-sensitivity immunoblotting and immunohistochemistry. [103] This study was limited by the fact that the median age of tonsillectomy specimens was less than 10 years and most of these patients would not have had a significant exposure to BSE.

A second study examined more than 16,000 tonsillectomy and appendectomy specimens from persons aged 10-30 years (the population at highest risk for variant CJD) and found 3 positive results, yielding a prevalence of 237 cases per million population. [99]

Studies have indicated that nearly 1 in 2000 people living in the United Kingdom are harboring latent variant CJD in their lymphoreticular system. It remains unknown whether there is disease progression or possibility of transmission. [104, 105, 106, 107]  These startling numbers are why citizens of bovine spongiform encephalopathy-infected countries are not allowed to donate blood in the United States. The United Kingdom mostly uses US-derived blood products.  

Neuropathology

The pathology of variant CJD shows relatively uniform morphologic and immunocytochemical characteristics, which are distinct from other forms of CJD (see the images below).

The florid plaque in the cerebral cortex in varian The florid plaque in the cerebral cortex in variant Creutzfeldt-Jakob disease comprises a dense core with a paler outer layer of amyloid fibrils surrounded by spongiform change (hematoxylin and eosin stain at low magnification). From Ironside JW, Frosch MP, Bernardino G. "Human prion diseases." In: Gray F, De Girolami U, Poirier J, eds. Escourelle & Poirier Manual of Basic Neuropathology. Philadelphia, Pa: Elsevier, 2004: 145-57.
The florid plaque in the cerebral cortex in varian The florid plaque in the cerebral cortex in variant Creutzfeldt-Jakob disease comprises a dense core with a paler outer layer of amyloid fibrils surrounded by spongiform change (hematoxylin and eosin stain at high magnification). From Ironside JW, Frosch MP, Bernardino G. "Human prion diseases." In: Gray F, De Girolami U, Poirier J, eds. Escourelle & Poirier Manual of Basic Neuropathology. Philadelphia, Pa: Elsevier, 2004: 145-57.
Immunocytochemistry for prion protein (PrP) shows Immunocytochemistry for prion protein (PrP) shows strong staining of the florid plaques and multiple smaller plaques and diffuse PrP deposits (low magnification). From Ironside JW, Frosch MP, Bernardino G. "Human prion diseases." In: Gray F, De Girolami U, Poirier J, eds. Escourelle & Poirier Manual of Basic Neuropathology. Philadelphia, Pa: Elsevier, 2004: 145-57.
Immunocytochemistry for prion protein (PrP) shows Immunocytochemistry for prion protein (PrP) shows strong staining of the florid plaques and multiple smaller plaques and diffuse PrP deposits (higher magnification). From Ironside JW, Frosch MP, Bernardino G. "Human prion diseases." In: Gray F, De Girolami U, Poirier J, eds. Escourelle & Poirier Manual of Basic Neuropathology. Philadelphia, Pa: Elsevier, 2004: 145-57.

The diagnostic pathological features of variant CJD are as follows [108] ):

  • Multiple florid plaques in hematoxylin and eosin sections; numerous small cluster plaques in prion protein–stained sections; and amorphous pericellular and perivascular prion protein accumulation in the cerebral and cerebellar cortex
  • Severe spongiform change; perineuronal and axonal prion protein accumulation in the caudate and putamen; and marked astrocytosis and neuronal loss in the posterior thalamic nuclei and midbrain
  • Marked astrocytosis and neuronal loss in the posterior thalamic nuclei and midbrain, and reticular and perineuronal prion protein accumulation in the gray matter of the brainstem and spinal cord
  • Reticular and perineuronal prion protein accumulation in the gray matter of the brainstem and spinal cord
  • PrPSc accumulation in lymphoid tissues throughout the body
  • Predominance of diglycosylated PrPSc in CNS and lymphoid tissues

Relative uniformity of the pathological and biochemical features in the brain is a striking feature of variant CJD and is in keeping with the relatively consistent clinical phenotype for this disease.

By contrast, for sporadic CJD, at least 6 neuropathological and biochemical subtypes have been identified. [109] Although the biochemical profile of PrPSc in variant CJD resembles that in bovine spongiform encephalopathy (BSE) and BSE-related disorders in other species, the neuropathology of variant CJD is distinct from BSE.

Florid plaques are a neuropathological, but not uniform, hallmark of variant CJD. However, smaller cluster plaques are observed in all cases and have not been reported in any other type of human prion disease. Rarely, florid plaques have occurred in iatrogenic CJD in dura matter graft recipients in Japan, but these cases do not show any other distinctive neuropathological features of variant CJD. [110]

Kuru-type amyloid plaques observed in patients with sporadic CJD who are heterozygotes at codon 129 in their PRNP gene can be distinguished from florid plaques by their restricted distribution in the cerebral cortex and cerebellum, smaller size, compact plaque morphology, and absence of the rim of spongiform change in the neuropil. [109]

The pattern of thalamic neuronal loss and gliosis is distinct. In variant CJD, pulvinar and dorsomedial nuclei are affected.

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Magnetic Resonance Imaging

There is large variability in MRI patterns that make "typical" patterns in variant CJD difficult to define. The majority of cases have cortical (frontal and parietal) and basal ganglia involement. MRI demonstrates certain unique features in variant CJD such as the "pulvinar sign" and the "hockey-stick sign.". [111, 112]  These findings are specific to variant CJD and, therefore, have been included in the World Health Organization (WHO) criteria for the diagnosis of variant CJD. [63] (See Staging, under Presentation.) DWI sequence is thought to be superior because of the detection of microvacuolation of neuritic processes causing spongiform degeneration. However, ADC sequence also seems to be important in differentiating between sporadic and variant forms.  [107]

In a study of 86 patients, 71% of T2-weighted images and 100% of fluid-attenuated inversion recovery (FLAIR) images showed positive pulvinar signs, as defined by symmetric hyperintensity of the bilateral pulvinars relative to the anterior putamen (see the image below). [113]

Pulvinar sign of variant Creutzfeldt-Jakob disease Pulvinar sign of variant Creutzfeldt-Jakob disease. Fluid-attenuated inversion recovery (FLAIR) image shows marked symmetrical hyperintensity of the pulvinar (posterior) thalamic nuclei, and this sign is present in 100% of cases imaged with FLAIR imaging. From Collie DA, Summers DM, Sellar RJ, et al. "Diagnosing variant Creutzfeldt-Jakob disease with the Pulvinar sign: MR imaging findings in 86 neuropathologically confirmed cases." Am J Neuroradiol, 2003;24: 1560-9.

Common additional MRI findings include hyperintensity of dorsomedial thalamic nuclei (93%), periaqueductal gray matter (83%), and caudate head. Dorsomedial and posterior thalamic hyperintensity bilaterally produces a characteristic hockey-stick distribution (see the images below). [111, 112, 113, 114]  However, this distribution of hyperintensity can also be seen in other forms of prion disease.

Axial fluid-attenuated inversion recovery (FLAIR) Axial fluid-attenuated inversion recovery (FLAIR) showing periaqueductal gray matter hyperintensity (arrow). Although not a specific sign, periaqueductal hyperintensity is observed in 83% of patients imaged with FLAIR imaging. From Collie DA, Summers DM, Sellar RJ, et al. "Diagnosing variant Creutzfeldt-Jakob disease with the Pulvinar sign: MR imaging findings in 86 neuropathologically confirmed cases." Am J Neuroradiol, 2003;24: 1560-9.
Hockey stick sign of variant Creutzfeldt-Jakob dis Hockey stick sign of variant Creutzfeldt-Jakob disease. Fluid-attenuated inversion recovery (FLAIR) image shows symmetrical pulvinar and dorsomedial thalamic nuclear hyperintensity. This combination produces a characteristic hockey stick appearance and is present in 93% of patients imaged with FLAIR imaging. From Collie DA, Summers DM, Sellar RJ, et al. "Diagnosing variant Creutzfeldt-Jakob disease with the Pulvinar sign: MR imaging findings in 86 neuropathologically confirmed cases." Am J Neuroradiol, 2003;24: 1560-9.

In contrast, MRI changes in sporadic CJD are usually more pronounced in the caudate and putamen, and the changes can be asymmetric. [115, 116] Rarely, hyperintensity in the pulvinar relative to other thalamic nuclei has been described in young patients with sporadic CJD, making the pulvinar more conspicuous. Although this could be mistaken for variant CJD, the signal intensity of the pulvinar always remains less than that of the anterior putamen. SPECT scans were studied in 2 patients and showed nonspecific hypoperfusion abnormalities. [117]

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Electroencephalography

Nonspecific diffuse background slowing is the most common finding on EEG. Periodic sharp and slow-wave complexes (PSWCs) are considered characteristic of Creutzfeldt-Jakob Disease (CJD), however they are less apparent in variant CJD. They may appear as early as 3 weeks after the onset of the disease and occur in 60-70% of all patients with sporadic CJD during the course of the illness. It was previously thought that PSWCs were frontal and bilateral, however growing evidence points to a more temporal location in the prodromal stage of disease. Global bifrontal appearance appears later in the disease. [107, 97]  PSWCs also occur in some cases of familial CJD but are absent in iatrogenic human growth factor hormone–related CJD, fatal familial insomnia, and Gerstmann-Sträussler-Scheinker syndrome.

Only one patient with variant CJD has been reported to show PSWCs. This was seen in a Japanese patient whose initial EEG showed diffuse slowing and a follow-up EEG performed 2 years later showed periodic complexes typical of sporadic CJD. [118]

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Other Tests

PET/CT seems to be a promising diagnostic tool and has been suggested as able to detect lesions better than MRI in earlier stages of disease. PET imaging could be even more useful in the near future by developing an in vivo probe to label prion plaques. [119]

Some studies have indicated the possiblity of detecting PrP in urine of patients with variant CJD. [97] . Moda et al. used protein misfolding cyclic amplification (PMCA) to replicate PrPsc and analyze the urine of patients with various transmissible spongiform encephalopathies. PrPsc was detected in 13 of 14 urine samples of patients with variant CJD and none in the other samples consisting of healthy controls and other neurological conditions. [120]

Unfortunately, CSF biomarkers are less sensitive than for sporadic disease type.

 

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Procedures

The gold standard for diagnosis is pathological confirmation via brain biopsy. However, the frequency of a positively diagnostic specimen is rather low. A CJD center in Germany evaluated 26 patients between 1993 and 2005 with suspected CJD and concluded 42% of the biopsies to be nondiagnostic. [121]  The reason for low diagnostic yield may be due to the methodology used where vacuolation is commonly missed in specimens. Safar et al. used a new technique called conformation-dependent immunoassay (CDI), which showed 100% accuracy and detection of PrPsc in any part of the brain. [122]  Biopsy has remained controversial due to both poor diagnostic yield and the fact that CJD remains untreatable. Manix et al. states that "brain biopsy should only be done after all noninvasive diagnostic avenues are exhausted, and do not point to a cause." [123]

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