This study was the first large-scale investigation of ADEM incidence in Nanchang, Jiangxi in China, and it could help us to understand the baseline ADEM incidence in Nanchang. The investigation showed that the average annual incidence of ADEM in Nanchang was 0.31/100,000, which is slightly lower than the incidence in San Diego between 1991–2000 (0.4/100,000), than the incidence among children with demyelination disease in Thailand between 1997–2006 (4.1/100,000)
, and then an estimation of 0.8/100,000
. However, the incidence was higher than the incidence among Germans (0.07/100,000)
. These results indicate that the incidence rates of ADEM differ among countries, most likely due to the differences in race, environment or climate.
In the population in Nanchang, the average age of onset was 33.40, and the median age was 25.97. The incidence was 0.55/100,000 among those over 60 years old, 0.47/100,000 among those under 14 years old, and 0.27/100,000 among those 15–59 years old. The incidence rate was 0.31/100,000 among males and 0.32/100,000 among females. Reportedly, ADEM mainly occurs in children younger than 10 years old
[3, 4] or mainly in children and young people
. Previous studies on ADEM have focused on children but rarely on adults. Among the children with demyelination disease in Thailand between 1997 and 2006, the incidence rate was 4.1/100,000, the average age of onset was 6.9 years old, and most of the patients presented with a preceding infection
. In Germany, the incidence rate of ADEM was 0.09/100,000 among children under 10 years old and 0.03/100,000 among children 10–15 years old. Thus, children 3–8 years old were the peak group of onset; the incidence rate was insignificantly higher in males than in females
. Banwell reported that ADEM mostly attacked children under 10 years old, but the incidence rates did not differ between the sexes
, and the median age of onset was 6.5
. The results of our study are similar to some other studies in the literature: ADEM may occur in any age group, and the incidence rate is insignificantly higher among children under 14 years old than among people older than 15 years old. The incidence rate is the highest among children 5–9 years old (0.75/100,000), followed by individuals older than 60 years old (0.55/100,000). Senile ADEM has rarely been reported
, which attracts our attention.
ADEM occurs most frequently in March (n = 7) and least frequently in April or July (both n = 2). It is easier for the residents to become infected with a precursor disease, such as a respiratory tract infection, because of the winter weather in Nanchang. In the northern hemisphere subtropical zone, it is coldest in January and February. In addition, the Chinese spring festival, the most important traditional festival in China, is often around February. People are often reluctant to go to hospital until spring festival is over. Thus, the number of patients may increase in March. When the 12 months were divided into 4 seasons, the incidence rates did not differ by season. This conclusion is slightly different from the conclusion that ADEM occurs more frequently in the spring and in the winter
[6, 22]. Preceding infections generally occur 2 to 60 days before the onset of ADEM
[3, 23]; two-thirds of the child patients had a preceding infection, one-sixth of the child patients had a history of inoculation
, and approximately 50% of the adult patients had no preceding infection. The viruses that cause infection mainly include measles, parotitis, urticaria, varicella-zoster virus, cytomegalovirus (CMV), Epstein-Barr virus, herpes simplex virus, hepatitis A or B, Coxsackie virus, influenza A or B, HIV, human T-cell lymphotropicvirus-1 (HTLV-1), human herpes virus 6
, and the bacteria are mainly pneumonia mycoplasma
. In this study, 15 patients (31.92%) had other diseases before the onset of ADEM (all were preceding infections); 6 patients under 14 years old (37.5%) and 4 patients older than 60 years old (40%) had preceding infections. The detected rates of infection with pathogens were consistent with previous studies.
ADEM often occurs after vaccination, so it is believed that ADEM related to inoculation most likely occurs because the inoculation induces autoimmune disorders that cause brain and spinal cord immune injuries. Inoculation with vaccines against hydrophobia (in particular), smallpox or measles
, type-B encephalitis, hepatitis B, pertussis, or influenza can cause ADEM, but cases caused by the influenza vaccine are rarely reported
[24, 28]. With vaccination, the total incidence rate of ADEM was 0.1-0.2/100,000
, lower than the incidence rate after infection with the measles virus (1:1,000)
. The incidence of ADEM was 1:1,000 - 1:20,000 after inoculation with the measles vaccine and 1:7,000-1:50,000 after inoculation with the rabies vaccine
. Only one of the 14.3 million inoculators in Sichuan, China in 2007–2008 had ADEM. The results of the study showed that no patients received a vaccination within 2 months before the onset of ADEM. In addition, the results of ecological study showed that an increased number of vaccination was not accompanied with a corresponding increased number of cases of ADEM. Because ecological study has some main limitations including ecological fallacy and difficult control of some confounding factors etc. The results of ecological study cannot provide strong evidence for an association between exposed factors and onset of the disease. Thus, the authors inferred discreetly the following conclusion with the existing research data: there was no evidence of an association between increased number of vaccines administered and number of cases of ADEM in Nanchang, China. It would be satisfactory if a cohort study on the association between vaccine and ADEM was performed.
In this study, the authors searched all the hospitals that could receive and cure ADEM patients, but some ADEM patients might not go to hospital. Some ADEM patients might have been missed, so the incidence of ADEM might be underestimated. The information in the medical records might be incomplete, and information bias might be present.