The lack of specific MRI abnormalities in anti-NMDA receptor encephalitis makes the identification of the most affected areas difficult. Functional neuroimaging could be useful to identify brain dysfunction associated with psychiatric symptoms, but few precise data are available up to now.
A 27-year-old woman was referred for recent behavioural changes and jerks of the right foot. Serial left fronto-temporal seizures were recorded. Identification of anti-NMDA receptor antibodies in CSF indicated a diagnosis of anti-NMDA receptor encephalitis. Two foci of hypermetabolism, in the left prefrontal cortex and the anterior cingulate cortex, were identified using 18-fluorodeoxyglucose PET and both disappeared after treatment. Brain MRI was normal, except for a mild left prefrontal hypersignal.
The increase in marker uptake in motor and premotor regions in our case probably corresponds to epileptic activity. Our data suggest that the anterior cingulate cortex could play an important role in psychiatric symptoms. Other studies are needed to better understand the pathophysiology of anti-NMDA receptor encephalitis.