Data are for 400 patients with anti-NMDAR encephalitis.

(A) Hippocampal neurons immunostained for surface and internal (total) N-methyl-D-aspartate receptor (NMDAR) clusters (top row, stained with commercial NR1 subunit antibody), surface NMDAR clusters only (middle row, stained with patients’ cerebrospinal fluid [CSF]) and their co-localisation (bottom row, surface NMDAR clusters in yellow). Treatment with patients’ IgG for 1 day decreases surface and total NMDAR cluster density compared with control IgG. Treatment with patient Fab fragments does not affect surface or total NMDAR cluster density, whereas treatment with divalent patient Fab fragments (Fab fragments and anti-Fab secondary antibodies) decreases surface and total NMDAR cluster density to an extent similar to patients’ IgG. (B) Effects of patients’ IgG, Fab fragments, and divalent Fab fragments on surface and total NMDAR cluster density. (n=30 cells, four independent experiments; two samples from patients, two samples from control patients with unrelated neurological disorders with no immune system involvement). All values are mean ± SE. *=significant difference (one-way ANOVA test followed by Bonferroni’s multiple comparison test, p<0·00071). (C) Graphic representation of the effect of each treatment on surface receptor clusters. (D) Representative average miniature excitatory postsynaptic currents (mEPSCs) recorded in magnesium (Mg2+)- free physiological saline with tetrodoxin (TTX) and picrotoxin to isolate synaptic NMDAR-mediated currents. In neurons treated with IgG from controls for 1 day, 2-amino-5-phosphonovaleric acid (APV), an NMDAR antagonist, blocks the slow decay of the mEPSC (dark green trace). The difference between the dark green traces is the slow NMDAR-mediated current. Neurons treated for 1 day with CSF from a patient (right) have no APV sensitive, NMDAR-mediated current (ie, no difference between the dark green traces). (E) Brain sections from rats infused with CSF from controls (top left) contain many NMDAR clusters in the cornu ammonis (CA1) of the hippocampus, whereas brain sections from rats infused with a patient’s CSF (top right) contain substantially fewer NMDAR clusters. Presynaptic synapsin immunostaining is similar between groups (bottom left, right). (F) Effect of 2-week-infusion of patients’ CSF with different antibody titres on NMDAR cluster density in CA1. Each point represents the mean NMDAR cluster density from three to five images from an infused rat, ±SE. Patients’ CSF with higher antibody titres reduced NMDAR cluster density to a greater extent than did lower titre samples. These findings indicate that infusion with patients’ CSF results in a titre-dependent decrease in NMDA cluster density (linear regression analysis; R²=0·32, p<0·03). All values are mean±SE. Data are for nine rats killed after 14 days of infusion; five CSF samples from patients, and four CSF samples from controls. (G) Hippocampal section from a healthy individual (left) and from a patient with anti-NMDAR encephalitis (right) immunostained with a commercial NR1 antibody. (H) Intensity of NR1 immunostaining is substantially reduced in the hippocampi of anti-NMDAR encephalitis patients (n=2) compared with hippocampi of controls (3). The distribution of both patient values for NR1 intensity differed significantly from the distribution of control values (paired Komolgorov-Smirnov test, p<0·03). All data adapted from Hughes and colleagues,⁶⁸ with permission from the Society for Neuroscience.

The figure is based on data from animal models of pharmacological or genetic decrease of NMDAR (N-methyl-D-aspartate receptor). Each step has been shown in these models or in individuals treated with antagonists of NMDAR. The pronounced resemblance with the clinical features of anti-NMDAR encephalitis leads us to postulate that an antibody-mediated decrease of NMDAR predominantly inactivates GABAergic neurons (which are rich in NMDAR), leading to disinhibition of excitatory pathways and increase of extracellular glutamate. As a result patients develop a frontostriatal syndrome, which is characteristic of anti-NMDAR encephalitis. The complexity of orofacial and limb movements in patients with this disorder is probably explained by disinhibition of a brainstem central pattern generator that under normal conditions is tonically inhibited by the GABAergic system.⁸⁵ Because genetic disruption of NR1 causes hypoventilation,⁸⁰ a direct effect of the antibodies on the medullary-pontine respiratory network (nuclei of Kölliker-Fuse) might result in breathing dysfunction.⁸³ The presence of NMDAR in dopaminergic, cholinergic, and noradrenergic systems probably explains the autonomic manifestations (hypersalivation, hypertension, hyperthermia, cardiac dysrhythmia) that are also typical of NMDAR antagonists.²⁶ Figure adapted from Florance-Ryan and Dalmau⁸⁶ with permission from Wolters Kluwer Health. GABA= γ-amino-butyric acid.

An 18-year-old man was transferred from another hospital after 4 weeks’ of being in coma. At admission, his CSF and serum were assessed at dilution 1 in 40 for reactivity with HEK293 cells that recombinantly expressed NR1/NR2 heteromers of the NMDAR. Only the patient’s CSF was positive (A). B shows the reactivity of a monoclonal antibody against NR1, and co-localises with patient’s CSF reactivity (merged immunolabelling in C). D shows that the patient’s serum did not react with cells expressing NR1/NR2; in E these cells are immunolabelled by use of a monoclonal antibody against NR1. F shows the merged reactivities. In C and F the nuclei of the cells are stained with DAPI. The graph shows NMDAR antibody titres in CSF over time. Titres were measured by ELISA for 13 months. CSF from control individuals with disorders other than anti-NMDAR encephalitis (eg, stroke, encephalitis suspected to be autoimmune, cerebellar degeneration, and viral encephalitis) were less than 500 relative fluorescence units (RFU; data not shown). The patient was treated initially with corticosteroids and intravenous immunoglobulin (IVIg) without improvement, and subsequently with rituximab and monthly cyclophosphamide. During the clinical course the brain MRI showed mild generalised atrophy. He is currently at home and able to take care of himself, have normal conversations, and play computer games, but is still recovering from symptoms of frontotemporal dysfunction. All techniques have been described elsewhere.⁸ CSF=cerebrospinal fluid. NMDAR=N-methyl-D-aspartate receptor.

First-line immunotherapy consists of corticosteroids, IVIg and plasma exchange given alone or in combination (detailed below). *Second-line immunotherapy, consists of rituximab or cyclophosphamide, or both. Substantial improvement is defined as previously reported,⁸ and includes full recovery or minimum deficits estimated by physicians and family members as recovery of more than 90% of function. All other patients are judged to have little improvement or no change. In patients with tumour, first-line treatment indicates tumour removal and in most cases first-line immunotherapy. Although there was no difference between the proportion of patients who achieved substantial recovery with or without tumour (Fisher’s exact test, p=0·16), patients with tumour responded to first-line treatment more often than did patients without tumour (p=0·001). Those without tumour required second-line immunotherapy more often and the 5 patients who died were in this group. Whether these patients had occult tumours is unknown.

In patients with anti-NMDAR (N-methyl-D-aspartate receptor) encephalitis, the processes of symptom presentation and recovery develop in opposite directions (A). The clinical picture is much the same as that caused by phencyclidine, in which the profile of symptoms correlates with the circulating concentration of drug (B). Since NMDAR antibodies cause a decrease of receptors that directly correlates with the titres, we postulate that the profile of symptoms during illness and recovery depends on the intensity of antibody-mediated decrease of NMDAR (C). The green receptors are NMDAR. The blue receptors are α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR). The small round vesicles that are released in the synapse are glutamate. PCP=phencyclidine.

*In women, ultrasound of abdomen and pelvis, or transvaginal unltrasound (if age-appropriate); in men, testicular ultrasound. †Mycophenolate mofetil or azathioprine for 1 year.‡Consider oral or intravenous methotrexate as an alternative immunosuppressant.¹⁰ Figure adapted from Florance-Ryan and Dalmau ⁸⁶ with permission from Wolters Kluwer Health.