DOI: https://doi.org/10.36347/sjmcr.2025.v13i12.016

Pages: 2960-2961

Background: Acute psychiatric onset in young adults requires systematic exclusion of organic etiologies, particularly autoimmune encephalitis and central nervous system (CNS) vasculitis, which frequently mimic primary psychotic disorders. Case Presentation: We report an 18-year-old male presenting with an acute neuropsychiatric syndrome combining agitation, aggression, hallucinations, persecutory delusions, and confusion, in a febrile context. Neurological examination revealed objective focal deficits, including right-sided pyramidal signs, left mydriasis, and left peripheral facial weakness. MRI demonstrated chronic structural lesions (left frontal porencephaly and left parietal atrophy) as well as new lacunar ischemic abnormalities in the right parietal white matter, consistent with an active process. Infectious investigations were unremarkable. Conclusion: This case underscores the importance of considering neuroimmune or vascular etiologies in any acute-onset psychiatric presentation, even when chronic cerebral sequelae are present. According to DSM-5, the appropriate diagnosis is Psychotic Disorder Due to Another Medical Condition. The combination of acute psychosis with objective neurological signs constitutes a major red flag requiring urgent etiological assessment and initiation of targeted immunomodulatory therapy.