In psychiatric clinical practice, we can face numerous organic diseases in the differential diagnosis between primary psychiatric disorders. As an example of this, we can see the autoimmune limbic encephalitis(LE), which in a significant percentage of cases begins with psychiatric symptoms. Currently, one of the theories of the origin of the LE is as a idiopathic autoimmune entity, leaving behind the idea of been generated only by a viral or paraneoplastic etiology.

To achieve a better knowledge about this underdiagnosed entity, presenting a case of an anti-LGI1 limbic encephalitis.

A 60-year-old Caucasian woman who starts with neuropsychiatric symptoms as: behavioral disorders, manic symptoms, memory impairment and attention deficit.

Finally, the diagnosis was confirmed when the patient had positive results in both serum and CSF samples for anti-LGI1 antibodies. Gastric neuroendocrino tumour type I was discovered. Neither paraneoplasic syndrome nor onconeuronal antibodies were shown. A thin hyperintense signal was identified in the left hippocampus using a brain MRI. Despite the patient had been treated with corticosteroids, immunosuppressants and immunoglobulins, she still showed positive antibodies in CSF samples with poor clinical results, especially psychiatric symptoms. The patient required one psychiatric hospitalization due to reference and persecutory delusions and manic symptoms.

Our patient had an unsatisfactory evolution with little response to immune treatment. Given the possible underdiagnosis of this condition, the importance of a differential diagnosis and an early treatment, we consider that there is an important need for a greater knowledge and scientific divulgation of this clinical entity.