Discriminating N-Methyl-D-Aspartate Receptor-antibody encephalitis (NMDAR-Ab-E) from primary psychosis

NMDAR-antibody encephalitis (NMDAR-Ab-E) is a condition in which the body mistakenly attacks a person’s NMDA receptors in the brain. These receptors are important in normal brain function including learning, memory, and normal conscious awareness. The antibodies reduce available receptors and so affect these functions. As the disease worsens breathing and heart function are affected meaning that some patients become critically unwell.  

People with NMDAR-Ab-E typically present with psychiatric symptoms and the symptoms can overlap with common severe mental illnesses. This makes diagnosis challenging and NMDAR-Ab-E is commonly misdiagnosed as a primary psychosis, delaying life-saving neurological treatments. Establishing which clinical features differentiate NMDAR-Ab-E from primary psychoses will improve diagnosis and care   for both groups.

The mental state examination (MSE) is a standardised clinical interview which forms part of the assessment of psychiatric and neurological disorders. We have looked at MSE data from a cohort of NMDAR-Ab-E positive patients and coded their symptoms using a standardised coding scheme. We now wish to collect the same data for patients presenting with a first episode of primary psychosis. To do this, we will extract mental state data such as symptoms and specific behaviours from case records of a psychosis early intervention service, using expert annotators to derive the information from free-text and code it using the same coding tool . The tool is a simple list of the features being present or absent and the level of confidence for that impression. We will then compare the two groups to determine which clinical features best discriminate between these diagnoses.