Anti N-Methyl-D-Aspartate receptor (NMDAR) encephalitis is an autoimmune disorder with a presentation that includes acute behavioral changes, psychosis, cognitive impairment and autonomic instability. In some cases, there are isolated psychiatric symptoms without neurological involvement.

To raise awareness of the disorder among psychiatrists, considering it a differential diagnosis in a first psychotic episode since a prompt diagnosis and treatment can dramatically affect the outcome.

To summarize the latest literature about this field and to present a case report.

A brief review of the latest literature was performed on PubMed using the keywords “anti N-methyl-D-aspartate receptor encephalitis”, “anti-NMDA encephalitis”, “psychiatric symptoms”.

A 20-year-old male was admitted to our inpatient unit with bizarre delusions of grandious and religious content, somatic hallucinations, sleep cycle inversion and strange behaviour. These symptoms had been present for 1 week and remitted after 10 days of treatment with risperidone. On follow-up, he developed anhedonia, apathy and blunt affect. Brain MRI showed multiple hyperintense changes in T2 and T2-FLAIR, highly suggestive of demyelinating lesions. The cerebrospinal fluid showed mild lymphocytic pleocytosis, mildly increased proteins, oligoclonal bands and anti-NMDAR antibodies of intrathecal production. He was treated with corticoids and the antipsychotic was discontinued. No neurologic symptoms were ever present.

This is an atypical case of anti-NMDAR encephalitis because of its isolated psychiatric presentation. Most patients develop neurological symptoms 2 to 3 weeks after onset of psychiatric symptoms. Monosymptomatic syndromes arise in less than 5% of patients.

The authors have not supplied their declaration of competing interest.