Diffuse Encephalitis Diagnosed on PET/CT Acquired in a Patient in Status Epilepticus with Negative MRI J Cain 1,2, J Hill 2, C Coutinho 2, S Mathur 2 1 University of Manchester, Manchester, UK, 2 Lancashire Teaching Hospitals, Preston, UK Excerpta Extraordinaire EE-03

Declaration I have no conflicts of interest to declare Dr John Cain Dr Sachin Mathur

Purpose To describe a case of encephalitis diagnosed on PETCT performed in a ventilated patient. The patient had previous and subsequent MRI within normal limits.

Case Report 23 year old previously well female presented with seizures, reduced GCS, left sided neglect and left focal motor seizures. A focal abnormality was identified in temporal region on EEG. Patient entered prolonged period of status epilepticus. Seizures not controlled with quadruple anticonvulsants. Intubated and ventilated on ICU.

Imaging Findings CT head – normal

Imaging Findings MRI Brain (initial) – normal Axial T2 DWI

Imaging Findings MRI Brain (initial) – normal Coronal FLAIR Post contrast T1

Imaging Findings PET/CT (FDG) – Diffuse reduced tracer uptake (hypo-metabolism) in posterior frontal, temporal, occipital and parietal lobes bilaterally, with relative sparing of the anterior frontal lobes and posterior fossa. Raw axial PET

Imaging Findings Fused attenuation corrected PET CT

Imaging Findings Follow up MRI 1 month after presentation: No focal signal abnormities, However there is moderate generalised atrophy which seem to have been progressive. Axial T2 Sagittal T1 Coronal FLAIR

Imaging Findings Follow up MRI 4 months after presentation: No focal signal abnormities, No obvious cortical abnormalities. Less pronounced atrophic changes compared to previous exam. Axial T2 Coronal FLAIR

LP findings Diagnosed with anti MNDA receptor encephalitis on CSF analysis. The remainder of the full body PETCT was within normal limits. No underlying malignancy identified.

Anti MNDA receptor encephalitis Discovered in 2005 Antibodies against NR1–NR2 heteromers of the NMDA receptor. Progressive illness presents with psychosis, memory deficits, seizures, and language disintegration. Later features coma, catatonic, abnormal movements, autonomic and breathing instability. The disorder predominantly affects adolescents and young adults mean 23, 7 to 1 F>M. Responds well to treatment but can relapse. High incidence of underlying tumour (e.g. ovarian teratoma) >75% of patients have substantial recovery that occurs in inverse order of symptom development associated with a decline of antibody titres.

Patient Outcome Patient made good recovery on immune modulating therapy. Discharged home. Slight persistent cognitive impairment. No associated malignancy was identified.

Summary PET/CT is able to detect hypo-metabolism in encephalitis even in the presence of normal MRI imaging. The case demonstrates a possible role of performing PETCT in such patients. The technical difficulties of performing a PET CT in a ventilated patient are less onerous than performing a MRI.

References Mohr, Brandt C., and Satoshi Minoshima. "F-18 fluorodeoxyglucose PET/CT findings in a case of anti- NMDA receptor encephalitis." Clinical nuclear medicine 35, no. 6 (2010): Dalmau, J; Lancaster, E; Martinez-Hernandez, E; Rosenfeld, MR; Balice-Gordon, R "Clinical experience and laboratory investigations in patients with anti-NMDAR encephalitis.” The Lancet. Neurology (1): 63–74