A Rare Case of Adult-Onset Acute Disseminated Encephalomyelitis Presenting with Seizure and Acute Confusion: A Case Report and Literature Review

Abstract

Acute disseminated encephalomyelitis (ADEM) is an immune-mediated inflammatory demyelinating disorder of the central nervous system, typically encountered in the pediatric population. Adult-onset ADEM is uncommon and poses a diagnostic challenge, particularly when presenting with seizure as a cardinal feature and when initially mimicking infectious meningoencephalitis. A 33-year-old previously healthy man presented with a first-ever generalized tonic–clonic seizure preceded by a 1-week history of frontal headache and acute-onset confusion. Infectious meningoencephalitis was initially suspected, and empiric antimicrobials were started. Initial laboratory investigations are summarized in Table 1. Cerebrospinal fluid analysis showed lymphocytic pleocytosis with elevated protein, while multiplex polymerase chain reaction testing for common viral, bacterial, and fungal pathogens was negative, as shown in Table 2. Brain magnetic resonance imaging revealed extensive, poorly marginated T2/fluid-attenuated inversion recovery hyperintense lesions involving the subcortical white matter, basal ganglia, bilateral thalami, midbrain, and cerebellar peduncle, as shown in Figures 1 to 4. Extensive infectious, autoimmune, and paraneoplastic workups were negative, including serum myelin oligodendrocyte glycoprotein immunoglobulin G and aquaporin-4 immunoglobulin G antibodies. The patient was treated with high-dose intravenous methylprednisolone and intravenous immunoglobulin, leading to rapid and complete clinical recovery. A follow-up magnetic resonance imaging was not performed because the patient achieved complete clinical recovery and remained asymptomatic during follow-up. Adult ADEM should remain a differential diagnosis in young adults presenting with a first-time seizure and encephalopathy, even without preceding infection or vaccination. Early recognition, exclusion of infectious mimics, and timely immunotherapy with corticosteroids, with consideration of intravenous immunoglobulin in severe cases, are critical for favorable outcomes.