Background: NMDA (N-methyl-D-aspartate, a glutamate receptor) receptor is involved in higher brain functions including learning and memory. Anti-NMDA receptor encephalitis is an autoimmune disorder with complex presentations that includes psychiatric symptoms, memory deficits and autonomic instability. It has been recognized as an important differential diagnosis in patients presented initially with psychiatric manifestations. Patients present variant signs that range from anxiety symptoms and seizure to unresponsive states, which may mislead diagnosis towards psychosis in the emergency department as this disease is a neurological disorder in psychiatric disguise. Case presentation: We present a case of a 6 years old girl with psychiatric manifestations in terms of change in behavioral aspects like being fearful, restless and anxious, which progressed to autonomic instability and decreased level of consciousness within days. EEG was carried out beside anti-NMDA receptor antibodies, and the patient was diagnosed with anti-NMDA receptor encephalitis, which was treated with monoclonal antibody (rituximab) and psychotropic medication, all symptoms subsided and full recovery was obtained after a few months. Conclusion: This case describes a treatable medical condition that may be missed in emergency settings. Hence, the awareness of this disorder is important for diagnosis as acute psychotic episodes. Correct diagnosis and right evaluation can lead to early intervention and better prognosis.

Keywords: Childhood psychosis, anti-NMDA receptor encephalitis, Autoimmune encephalitis, Paraneoplastic neurological syndromes, acute psychosis, case report