To the Editor: Limbic encephalitis is characterized as a syndrome of acute to subacute onset with neuropsychiatric symptoms and medial temporal lobe abnormalities on MRI and/or EEG.^{1, 2} Symptoms include sleep changes, confusion, irritability, hallucinations, depression, personality changes, and cognitive impairment.¹ Most common causes are infectious, autoimmune, and paraneoplastic.² Herein, we present a case of limbic encephalitis with an initial presentation of psychosis which was previously misdiagnosed as medication induced psychosis and bipolar disorder.

A 48 year old married Hispanic female presents with a one month history of intermittent psychotic symptoms which began after starting treatment for bronchitis. Prior to this, she had no psychiatric history and had a high level job as editor of a local newspaper. She was started on a 7 day course of Fluticasone/Salmeterol and Montelukast by her pulmonologist, and soon after, began having auditory hallucinations and religious delusions. She was admitted to a local psychiatric hospital and was diagnosed as having had an adverse reaction to Montelukast. The medications were discontinued and she was discharged with no psychotropic medications. After discharge, she continued to have psychotic symptoms and was admitted to a second local hospital. Basic labs and CT head were normal. On MRI, she was found to have a 6mm enhancing lesion in the right posterior lentiform nucleus and on EEG was found to have right temporal sharp waves. She showed improvement in psychotic symptoms and was allowed to sign out AMA prior to completion of the work-up. One week later, the psychotic symptoms persisted and she was brought to the Mental Health Crisis at Jackson Memorial Hospital involuntarily by police. On initial presentation, she was grossly psychotic with auditory hallucinations and religious delusions. She had discrete episodes of agitation, religiosity, and aggression toward self and others with no subsequent recollection of the events. She was started on Olanzapine 10mg daily and Divalproex 500mg bid. Due to the abnormal presentation of her symptoms, hospital records were obtained and the neurology service was consulted. Upon review of the records and neurological evaluation, she was diagnosed with limbic encephalitis and immediately transferred to the neurology service for further evaluation and initiation of IV acyclovir therapy.

This case illustrates that psychiatric symptoms, such as psychosis, can be part of the initial presentation in patients with limbic encephalitis. It is vital to exclude neurological diseases in patients with no known history of psychiatric illness, presenting with acute onset psychosis and personality changes.³ A prodomal period resembling viral illness should further heighten the degree of suspicion of an organic etiology.⁴ Diagnostic testing should be ordered on patients presenting with such neuropsychiatric symptoms including CSF analysis, MRI, EEG, and laboratory studies. MRI findings in limbic encephalitis are varied and in a majority of patients, no abnormalities are detected. EEG may show sharp epileptiform activity, and CSF analysis is helpful in determining underlying viral pathophysiology.³ Further work-up to rule out auto-immune (anti-NMDAR, anti-VGKC, anti-Hu antibodies) or a paraneoplastic cause (ovarian teratoma, small cell lung cancer, breast cancer) should also be conducted.⁴