Abstract
Objectives To establish the diagnostic yield of electroencephalogram (EEG) and other investigations for evaluation of limbic encephalitis in patients with new onset psychiatric symptoms.
Methods A retrospective audit was conducted of all EEGs performed between July 2020 to August 2021 for workup of new-onset psychiatric symptoms at a tertiary neurology referral centre. Data was obtained from electronic medical records including patient history, neurological examination findings, results of investigations including EEG, brain magnetic resonance imaging (MRI), cerebrospinal fluid (CSF), serum autoantibodies and final clinical diagnosis.
Results 82 patient requests were identified, 9 outpatients and 73 inpatients. 8 patients (10%) had an abnormal EEG: 1 showed epileptiform abnormalities (patient already known to have epilepsy) and 7 showed non-specific slowing (generalised in 3 and focal in 4)n. 5 of 38 patients (13%) with brain MRI had structural abnormalities demonstrated. 2 out of 46 patients (4%) tested for anti-neuronal antibodies had low-titre VGKC autoantibodies, both determined to be false positive results. No patients had abnormal neurological signs apart from confusion or drowsiness. No patients had a final diagnosis of limbic encephalitis.
Conclusions While evaluation for epilepsy or limbic encephalitis is important in patients with new onset psychiatric symptoms this audit demonstrates that yield of neurological investigations for evaluation of limbic encephalitis in general psychiatric presentations is low. Careful patient selection using clinical criteria such as described by Graus, et al . may increase the yield and reduce the burden of investigations on the public health system.
