Pediatric Acute Disseminated Encephalomyelitis Triggered by Concurrent Administration of Seasonal and H1N1 Influenza Vaccines: A Case Report and Review

Abstract

Background: Acute disseminated encephalomyelitis (ADEM) is a rare, immune-mediated inflammatory disorder of the central nervous system (CNS), typically characterized by the acute onset of multifocal demyelination. The pathogenesis of ADEM remains unclear, but it is believed to be triggered by an autoimmune response, often following viral infections or vaccinations.

Case report: This case report describes a 3-year-old child who developed ADEM after receiving two concurrent influenza vaccines: one for seasonal influenza and one for the 2009 H1N1 pandemic. The patient presented with motor regression, mild pleocytosis in cerebrospinal fluid (CSF), and typical MRI findings of ADEM. Steroid pulse therapy resulted in rapid improvement, and the patient recovered fully without sequelae.

Results: Although the influenza vaccine has been linked to ADEM in some studies, it remains uncertain whether the simultaneous administration of both vaccines contributed to the onset of ADEM. While influenza vaccines are considered safe and effective by health organizations such as the CDC, data suggest that the incidence of ADEM and other neurological complications is significantly higher after natural influenza infections compared to vaccination. This highlights the importance of vaccination in preventing severe outcomes.

Conclusions: This case underscores the importance of monitoring and reporting adverse events following vaccination to refine our understanding of rare complications like ADEM. While simultaneous vaccine administration warrants further research, the benefits of vaccination in preventing severe complications from natural infections far outweigh the risks. Continued vigilance and improved surveillance systems are essential for maintaining public confidence in vaccination programs.

Keywords: ADEM; H1N1; MRI; autoimmune encephalitis; child; immunological response; influenza vaccine.

Figure 1

Brain MRI on Admission and Discharge (Spin Echo Method: Fluid Attenuated Inversion Recovery; FLAIR Axial: TR = 9000, TE = 104, FA = 150): (A,B): On admission, brain MRI with the Fluid Attenuated Inversion Recovery (FLAIR) sequence revealed high-intensity lesions bilaterally beneath the cerebral cortex, with asymmetrical involvement. FLAIR imaging, designed to suppress cerebrospinal fluid signals, provides enhanced visibility of brain parenchyma abnormalities, particularly those involving edema or inflammation. The bilateral, asymmetrical nature of the lesions suggests a possible systemic or multifocal pathology. These lesions are characterized by abnormal fluid accumulation, which appears bright on FLAIR images due to the suppression of CSF, allowing for better delineation of tissue abnormalities. (C,D): On follow-up MRI at discharge, these lesions had significantly improved, with reduced intensity in the previously affected areas. The reduction in signal suggests a decrease in underlying edema or inflammation, reflecting a positive change in the brain’s condition. This improvement highlights the effectiveness of follow-up imaging in monitoring the resolution of abnormalities over time.

Figure 2

Proposed Mechanism of Vaccine-Induced Acute Disseminated Encephalomyelitis (ADEM).