Incidence of and Mortality Due to Human Prion Diseases in Taiwan: A Prospective 20-Year Nationwide Surveillance Study from 1998 to 2017
This article was published in the following Dove Press journal: Clinical Epidemiology
Yu Sun 1,2 Chih-Ching Liu3, * Ling-Yun Fan4, * Chung-Te Huang5 Ta-Fu Chen2 Chien-Jung Lu1,2 Wan-Yuo Guo 6,7 Yang-Chyuan Chang2,8 Ming-Jang Chiu 2,9
Department of Neurology, En Chu Kong Hospital, New Taipei City, Taiwan; 2 Department of Neurology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan; 3 Department of Healthcare Administration, College of Medical and Health Science, Asia University, Taichung, Taiwan; 4 Queensland Brain Institute, University of Queensland, St. Lucia, Brisbane, QLD, Australia; 5 Center for Research, Diagnostics and Vaccine Development, Taiwan Centers for Disease Control, Taipei, Taiwan; 6 Department of Radiology, Taipei Veterans General Hospital, Taipei, Taiwan; 7 School of Medicine, National Yang-Ming University, Taipei, Taiwan; 8 Department of Neurology, Min-Sheng General Hospital, Taoyuan, Taiwan; 9 Graduate Institute of Brain and Mind Sciences, College of Medicine, National Taiwan University, Taipei, Taiwan; 10Graduate Institute of Psychology, College of Science, National Taiwan University, Taipei, Taiwan; 11Graduate Institute of Biomedical Electronics and Bioinformatics, National Taiwan University, Taipei, Taiwan
*These authors contributed equally to this work
Correspondence: Ming-Jang Chiu Tel +886-2-23123456 ext 65339 Fax +886-2-23418395 Email
mjchiu@ntu.edu.tw
Introduction: Epidemiologic studies of Creutzfeldt-Jakob disease (CJD) have been undertaken worldwide since the new variant CJD outbreak in 1996 in the United Kingdom. A nationwide report system, the Creutzfeldt-Jakob Disease Surveillance Unit (CJDSU), directed by the Centers for Disease Control of Taiwan, was established in 1997 to identify human prion diseases.
Methods: From 1998 to 2017, 647 cases were referred to the committee for confirmation. The report to CJDSU included a structured questionnaire recording the clinical, demographic data, and potential iatrogenic exposure, and the results of the clinical and laboratory examination, including tests of blood and cerebrospinal fluid, electroencephalography, and brain magnetic resonance imaging.
Results: In total, 356 cases (women, n=178) were ascertained to be human prion diseases, and 97.4% (n=347) were sporadic CJD, including three definite, 314 probable, and 30 possible cases; one probable variant CJD and 8 cases of the genetic form human prion diseases. The age- and gender-specific average annual incidence were also significantly higher in the second decade (0.95/1,000,000) than in the first decade (0.63/1,000,000), with an incidence rate ratio of 1.51. The incidences increased with increasing age, reaching a peak at the age of 70–79 years. The 10-year survival curve for sCJD patients showed that the 1-, 5-, and 10-year cumulative survival rate were 52%, 5%, and 1%, respectively. PRNP polymorphisms in 170 patients showed that 98.8% were M129M and 97.6% E219E.
Discussion: The significant increase in incidence after 2008 suggests the increase in the awareness of this rare disease among physicians. The longer disease duration in patients with sCJD in Taiwan than in other countries indicates that the comprehensive support of the health care system, as well as the end-of-life care culture in Taiwan, may prolong survival time in patients with such a progressive and fatal disease.
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Discussion
Our previous epidemiological research of CJD from 1998 to 2007 has been reported 10 years ago.3 In current analysis, we rechecked the information of all the ascertained cases of the first decade in the registry and found that 9 cases before 2005 should be excluded because they could not meet the diagnostic criteria with some missing data. Moreover, 2 cases that were identified in 2008 actually had their disease onset in 2007 by tracing their history again.
The overall incidence rate of CJD from 1998 to 2017 in Taiwan was 0.79 per million persons. The incidence significantly increased after 2008 to approximately 1 case per million persons per year, comparable to the worldwide incidence, typically reported to be approximately 1–2 per million person-years based on surveillance from 2005 onward.2,20 The increase in incidence for the second decade could be explained by the enhanced awareness of clinical physicians, the improved diagnostic tests, and the increase in the aging population in Taiwan, as the incidence of CJD cases, peaked in the 70- to 79-year-old age group similar distribution to the USA study. 21 The incidence of CJD onset after 80 years of age was still high, without a sharp decline, which was different from other reports.6,22 Since the start of the CJDSU in 1997, several national or international symposiums focused on human transmissible spongiform encephalopathy have been held by the Taiwan Neurological Society to educate neurologists and general physicians about the updated diagnostic criteria and management of CJD patients. The Taiwan CDC has regularly revised the workbook.23 In 2008, an imported case of vCJD was reported to CJDSU.19 This first acquired case of CJD in Taiwan was a critical public health concern and might have helped raise awareness of the disease among neurologists, leading to an increase in the number of reported cases afterward. In 2009, an updated set of criteria, including MRI findings, were proposed and soon adopted by the CJDSU.17 The pattern of high signal intensity had high sensitivity and specificity for the differential diagnosis, assisting in distinguishing sCJD from other neurological diseases and helping clinicians detect suspected cases early; this, in part, resulted in the increase in the number of referrals in subsequent years.
The polymorphism at codon 129 (M129V) of PRNP is a recognized genetic marker for susceptibility to CJD in Caucasians.24 In Europe, 51% of the general population has methionine/valine (MV) heterozygosity, while 37% has methionine homozygosity (MM).25,26 In East Asia, the MM genotype was found in 94% of Koreans27 and 92% of Japanese individuals.26 Ethnic Han Chinese, who account for over 95% of the Taiwanese population, has a remarkably high frequency (98%) of methionine homozygosity in the general population.28 Methionine homozygosity is high in both healthy individuals and diseased patients, with 98.8% of CJD patients in our study having the MM genotype and less than 2% carrying the MV genotype. Prion susceptibility and protective alleles can exhibit marked geographic differences, with the effects being different in the Asian and Caucasian populations.26
Because of the short disease duration in most cases, the increase in mortality with time parallels the temporal trend in incidence, as the mortality rate was significantly higher in the second decade than in the first decade. There was no difference in the incidence and mortality rates between men and women in our study. Some countries reported a higher incidence in women than men because of the larger number of women among older populations.21 The disease duration varied based on CJD types, with a relatively chronic course in some genetic forms. The mean survival time was 56.4 (range, 35.1–67.4) months in four GSS patients (P102L), 15.4 (9.0, 21.7) months in two E196A patients, and 11.9 months in an R148H patient, while a substantially shorter disease duration of 2.4 months was noted in a patient with a 72-base pair insertion. Because of the small number of gCJD patients in our study, it is challenging to compare Taiwan with other countries regarding these patients’ survival time.
Among the patients with sCJD, women and those with younger ages at onset had longer disease durations. This finding is comparable with the results from a collaborative multi-national CJD surveillance program (EUROCJD) conducted by the European Union and allied countries. The precise mechanisms underlying the effects of age and gender effects on survival time are not known. Agerelated variations in care or resistance to terminal infections have been proposed as possible explanations.29 Whether gender-specific factors influence the disease duration needs to be studied. In this national cohort, we found some long-term survivors of sCJD, with 3-, 5- and 10-year survival rates of 13%, 5%, and 1%, respectively. The median survival time was 13.5 months (mean: 19.1 months), and 48% died within one year of onset. Our data were similar to those in the report from Japan, in which the mean survival time of sCJD patients was 15.7 (range: 1–126) months, and 46.0% of all patients with prion disease died within one year. 29 However, reports from other counties revealed a much shorter survival time. The study by the EUROCJD involving 2,451 sCJD patients showed that the median survival time was five months (range: 1–81), and 85.8% died within one year of onset.11 The median duration in a study involving 150 definite or probable sCJD cases in Argentina was 4.6 (range: 1–70) months,30 while a Swedish study involving 123 patients with prion disease found that 74.6% of patients died within one year. 31 A study from China also showed a short survival time, with a median duration of 7.1 months (range: 1.0–23.3), and 78.5% of patients died within one year of onset.10
within one year of onset.10 The survival times of patients with sCJD in Taiwan and Japan were relatively longer than those reported in most of the other countries in the world. Japanese researchers explained the prolonged survival as the effects of their robust public medical insurance system and a culture allowing patients with end-stage neurological disease to receive intensive life-sustaining treatments such as tube feeding and intravenous high-calorie infusion.9,32 Taiwan adopted a single-payer National Health Insurance (NHI) system in 1995 that also provides comprehensive healthcare support.33 Patients with human prion disease do not need to pay any co-payment for outpatient or inpatient care. In addition, Taiwanese also share this end-of-life care culture.
There are several limitations to the current study. First, the percentage of definite cases of human spongiform encephalopathies was relatively small. Because of the traditional ethical values among the general population in Taiwanese society, the very low autopsy rate has long been acknowledged as an unfortunate and unavoidable reality. In recent years, using the real-time quaking-induced conversion assay to detect the pathological prion protein in the CSF or other tissues has been developed and has high diagnostic accuracy. 34 However, this technique was not used by the CJDSU in Taiwan during our study period. Without obtaining tissue specimens or testing for the pathological prion protein, we are not only unable to make a definite diagnosis but also are unable to assess the various molecular subtypes of sCJD, which is useful for phenotypic classification. Second, underreporting and underestimation of CJD are inevitable. Because of the older age at onset, patients with CJD may be misdiagnosed with other diseases with the rapid progression of neurological symptoms such as stroke,35 encephalitides,36 degenerative dementia,37 and epilepsy. 38 A retrospective archival survey published in 1995 showed that only approximately 60% of prion disease patients with pathologically spongiform encephalopathy were diagnosed clinically while alive. In recent decades, diagnostic accuracy has been improved by the use of CSF biomarkers and brain MRI.17 Not infrequently, the committee recommended that the primary care physician follow-up during the clinical course and perform MRI/EEG in case of uncertainty. They were obliged to report back at the next relevant meeting.
Furthermore, due to our NHI system’s comprehensive coverage, patients with spongiform encephalopathy received complete financial support covering all necessary MRI or EEG follow-up. There is nearly a consensus in clinical practice among neurologists in Taiwan that for those patients with rapid cognitive decline, in addition to CSF studies, MRI and EEG examination, tests to exclude autoimmune encephalitis or paraneoplastic encephalopathy should usually be performed. Third, the finding of 2% (8/356) of gCJD among all CJD forms was far lower than the corresponding figures elsewhere in the world, which range from 10–14%.25,39 Although the incidence of gCJD varies considerably among countries, we speculate that the lower proportion of gCJD in our study is likely because the PRNP gene sequencing test was not routinely performed before 2009, only 170 of the 356 CJD cases tested. Approximately 60% of genetic CJD cases were reported in patients with no family history, suggesting that they could have been misclassified in the absence of the PRNP genetic analysis.39
In conclusion, this study reports the 20-year epidemiologic features of CJD in Taiwan. The second decade’s incidence rate was comparable with the corresponding figures in most other countries in the world. The significant increase in incidence after 2008 suggests the increase in awareness of this rare disease among clinical physicians and the increase in Taiwan’s aging population. The longer disease duration in patients with sCJD in Taiwan than in Western countries indicates that the healthcare system and end-of-life care culture in Taiwan may prolong survival time in patients with such a rapidly progressive and fatal disease.
Keywords: human prion diseases, spongiform encephalopathy, incidence, mortality, disease duration
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