“Hopping Mad” 4-year-old: frog hallucinations or encephalitis?

Background : While most children presenting with undifferentiated nightmare-like symptoms may commonly suffer from conditions like parasomnias or neurodevelopmental disorders (NDDs), clinicians must not forget to consider exclusionary diagnoses like seronegative autoimmune encephalitis (SAE). Case Presentation : This case presents a 4-year-old girl with acute visual hallucinations, an episode of unresponsiveness with shuffling movements, and a month-long history of increased falls and intermittent slurred speech. Although having no presenting deficits, her history of hallucinations and abnormal movements prompted further neurologic evaluation. During her hospital course, she developed a multitude of new concerning features including hallucinations, slurred speech, and new ataxia, along with a vEEG revealing left parietal slowing with interictal epileptiform discharges. Conclusions : While MRI and CSF studies—including autoimmune panels—were normal, she was treated empirically with IV steroids and IVIG for suspected seronegative autoimmune encephalitis. Prior to discharge, autoimmune serum testing revealed elevated IL-2 receptor and IL-6 levels, supporting an inflammatory process despite seronegativity. Following treatment, her hallucinations resolved and gait deficits steadily improved with therapy. This case demonstrates the diagnostic complexity of SAE in young children with nonspecific neuropsychiatric symptoms as well as the vitality of maintaining broad differential approaches in an emergency setting.