Deep Brain Stimulation (DBS) of the Nucleus Accumbens for Treatment Resistant Severe and Enduring Anorexia Nervosa: A Phase 1 Open Trial

The aims of this study are to determine the efficacy of Deep Brain Stimulation in treatment-resistant severe and enduring anorexia nervosa. Surgical Procedure: Participants will have the Vercise Gevia Deep Brain Stimulation System surgically implanted by a neurosurgeon according to standard stereotactic procedures. All patients will undergo bilateral implantation. Device implantation is permanent and participants will have the option to continue with the therapy post-trial or have the device switched or and/or removed. The device provides electrical stimulation to the Nucleus Accumbens (NAcc). Stimulation is provided by controlled delivery of current from a battery in an implantable neurostimulator (INS) connected by extension leads from the body through the neck to electrodes surgically implanted in the brain. Stimulation programs are controlled by the neurologist via the clinical programmer. The total procedure is approximately 3.5 hours in duration. As in the standard procedure patients are woken intra-operatively and will also complete an image recognition task. Randomisation to ON or OFF stimulation in the blinded phase will occur at this time point in a 50:50 ratio. Randomisation will take place externally and allocation will be concealed from participants and investigators, excepting those responsible for DBS programming. Post-operatively participants will undergo a CT scan to verify electrode positioning. Stimulation / Programming: Participants will visit the centre for programming of the device by the neuropsychiatrist. Programming sessions will last approximately 30 minutes and are initially weekly, becoming less frequent when parameters are stable. Initial stimulation will commence bilateral stimulation, monopolar configuration. The clinician will initially review the response at weekly-fortnightly intervals. During initial phase aim is to increase stimulation amplitude by 0.5mA to 1mA per visit until a target amplitude of 4MA is reached. If there is an insufficient response after initial phase amplitude will be increased in 0.2mA to 0.5mA increments. Clinical Assessments: Assessment sessions are scheduled every 3 months. The following will be administered: * Eating Disorder Examination Questionnaire (EDE-Q 6.0) * Depression Anxiety and Stress Scale (DASS) * Yale-Brown Obsessive Compulsive Scale (Y-BOCS) * Montreal Cognitive Assessment (MoCA) * Clinical Impairment Assessment Questionnaire (CIA) * Body Mass Index (BMI) Patients will attend a clinic at the Royal Brisbane & Women's Hospital. The clinic will take approximately 1 hour and will be with the trial's psychologist. Image Recognition Task: Every 3 months participants will also undergo an EEG with a researcher at the Queensland Brain Institute. Under the EEG condition participants will complete an image presentation task. This session will take approximately 1 hour.