Screening for antibodies against the NMDA 3 receptor is indicated in cases of suspected encephalitis or for the differential diagnosis of autoimmune encephalitis. Seizures can be an early symptom of these conditions.
Antibodies against the NMDA receptor (NR1 subunit) are indicative of autoimmune encephalitis. The NMDA receptor (N-methyl-D-Aspartic) belongs to the family of ionotropic glutamate receptors and is widely expressed in the temporal lobe (limbic system). Signaling initiated by binding glutamate to the NMDA receptor is important for synaptic plasticity and cognitive functions such as memory and learning. The subacute change of personality affecting cognitive functions, hallucinations, epileptic seizures, strange behavior, impaired memory, and orientation disorder are examples of symptoms that may indicate autoimmune encephalitis if infectious etiology can be ruled out. Autoimmune encephalitis can be associated with malignancy.
Encephalitis positive for antibodies against the NMDA receptor often affects young women but can occur at all ages in both sexes. NMDA antibodies can be associated with ovarian teratoma (or male testicular teratoma) with reported incidence ranging from 9-56%. Early diagnosis and treatment are important before permanent tissue damage is established, as autoantibodies are considered pathogens. The specific antibody titer against NMDA can be used to monitor the efficacy of the treatment.
In general, immunotherapy treatment is more effective against autoantibodies directed to extracellular antigens than autoantibodies against intracellular antigens. Long-term treatment may be required for several months or even years, as well as monitoring of underlying cancer.
It is recommended that NMDA receptor antibodies be tested also in the cerebrospinal fluid (CSF).