summarises the clinical information. 86 patients who could be assessed had headache, low-grade fever, or a non-specific viral-like illness within 2 weeks before hospital admission. 77 patients presented with prominent psychiatric symptoms, including anxiety, agitation, bizarre behaviour, delusional or paranoid thoughts, and visual or auditory hallucinations. 23 presented with short-term memory loss or seizures alone or associated with psychiatric manifestations.
Characteristics and clinical features
During the first 3 weeks of symptom presentation, 76 patients had seizures. 88 patients developed decreased consciousness, progressing to a catatonic-like state, with periods of akinesis alternating with agitation, and diminished or paradoxical responses to stimuli (eg, no response to pain but resisting eye opening). Some patients mumbled unintelligible words or had echolalia. Eye contact or visual tracking was absent or inconsistent. During this clinical stage, large proportions of patients developed dyskinesias, autonomic instability, and central hypoventilation (median time of ventilatory support, 8 weeks; range 2–40 weeks). Orofacial dyskinesias were the most common; these included grimacing, masticatory-like movements, and forceful jaw opening and closing, resulting in lip and tongue injuries or broken teeth. 37 patients had cardiac dysrhythmias, including tachycardia or bradycardia, with prolonged pauses in seven patients; four needed pacemakers. 52 patients had dyskinesias, autonomic instability, and hypoventilation, 27 patients had two of these symptoms, and 14 had just one; the remaining seven patients developed a milder syndrome of seizures and psychiatric symptoms.
shows EEG, brain MRI, and CSF findings. 92 patients had extensive EEG monitoring, 77% had generalised or predominantly frontotemporal slow or disorganised activity (delta-theta) without epileptic discharges. Of the 100 patients, 55 had increased signal on MRI fluid-attenuated inversion recovery or T2 sequences; 14 of these patients had faint or transient contrast enhancement of the cerebral cortex, overlaying meninges, or basal ganglia. These findings were limited to a single area of the brain in 19 patients: 16 had abnormalities in medial temporal lobes, two in the corpus callosum, and one in the brainstem. Follow-up studies in 70 patients showed that many of those who recovered or were left with mild deficits had improved or normalised MRI (webappendix).
Ancillary tests and treatment
14 patients had brain biopsy: findings for two were normal, 12 showed mild perivascular lymphocytic cuffng, and ten microglial activation. All had negative results for neuronophagic nodules and viral assays.
58 (59%) of 98 patients had a neoplasm (); two died before tumour assessment. All but one of these patients developed neurological symptoms before the tumour diagnosis (median 8 weeks, range 1–380 weeks). In six patients, the tumour was diagnosed after recovery from the encephalitis (56–380 months). Ovarian teratoma identified with CT, MRI, or ultrasound was a common tumour type (median size 6 cm, range 1–22 cm). Eight patients had bilateral teratomas; four were synchronous, two had history of a contralateral teratoma, and two developed contralateral teratomas before recurrence of the encephalitis. All teratomas contained nervous tissue; 25 were examined for expression of NMDA receptors, and all were positive (data not shown).
One boy (11 years old, without tumour) and 21 women and girls were younger than 19 years (median 15 years, range 5–18 years); 12 had an ovarian teratoma (five with immature features), and nine had no tumour. Metastases were identified only in one man with immature teratoma of the testis.
Seven patients with cancer did not have tumour resection (one small-cell lung cancer, two teratomas found at autopsy, four not removed). Six patients who had tumours removed did not receive immunotherapy (). 40 of 42 patients without tumour had immunotherapy and two had supportive care.
Median follow-up was 17 months (1–194 months): 47 patients had full recovery, 28 mild stable deficits, 18 severe deficits, and seven died as a result of the neurological disorder. Patients whose tumour was identified and removed within the first 4 months of the onset of the neurological disease had better outcome than the rest of the patients (). The median time from symptom presentation to initial signs of improvement was 8 weeks (range 2–24 weeks) for the group of patients with early tumour treatment, 11 weeks (4–40 weeks) for the group whose tumour was treated late or not treated, and 10 weeks (2–50 weeks) for the group without tumour (Kruskal-Wallis, p=0.10)
The median duration of hospitalisation was 2.5 months (range 1–14 months). While hospitalised, seven patients had high levels of serum creatine kinase, six developed pulmonary embolism, six transient aphasia, four hemiparesis, and four tetraparesis. After discharge, 64 (85%) of the 75 patients who were left with mild deficits or eventually attained full recovery had signs of frontal-lobe dysfunction including poor attention and planning, impulsivity, and behavioral dysinhibition; 20 (27%) had prominent sleep dysfunction, including hypersomnia and inversion of sleep patterns.
15 patients had one to three relapses of encephalitis (webtable 2). The median time between initial presentation and last relapse was 18 months (1–84 months). Relapses were less common in patients with early tumour treatment (1 of 36) than in other patients (14 of 64; p=0.009), including patients whose tumour was treated late (six of 22; p=0.009) and patients without tumour (eight of 42; p=0.03). None of the patients was receiving immunotherapy at the time of the neurological relapse.
Seven patients died of the neurological disorder (webappendix), although the diagnosis was established retrospectively by examining archived CSF for all of them.
Analysis of the reactivity of patients’ sera or CSF against the indicated NMDA-receptor subunits or heteromers showed that antibody reactivity was not modified by changing the NR2 subunit (A, B, C, or D) and was retained by homomers of NR1 (webtable 3). Having established that NR1 was recognised by all patients’ antibodies, we investigated the epitope region by use of a plasmid (NR1d4) that encodes an NR1 subunit lacking amino-acid residues 25–380 that can nevertheless assemble with NR2B. The successful expression of NR1d4–NR2B in HEK293 cells was confirmed by immunocytochemistry with the indicated mouse and rabbit antibodies against NR1 and NR2B (data not shown). The use of these heteromers abrogated the reactivity of sera or CSF from 92 patients’, and substantially decreased the reactivity of the samples of the remaining eight cases. Hence the main epitope region recognised by all patients’ antibodies lies within the extracellular region of the NR1 subunit (webtable 3).
To determine whether patients had intrathecal synthesis of antibodies, we first measured the integrity of the blood–brain barrier.15
Of 58 patients with paired serum and CSF available, 53 had preserved integrity of the blood–brainbarrier. Analysis of normalized concentrations of IgG showed that all 53 patients had higher concentrations of antibodies in CSF than in sera, indicating intrathecal synthesis of antibodies (). Of the 83 patients whose CSF was available, those with tumours had higher antibody titres than those without (). Four patients who died and whose CSF was available were among the group with the highest titres, whereas the seven patients with milder syndromes had the lowest titres (data not shown). Patients who improved had a parallel decrease of serum titres, whereas those who did not improve maintained high titres in CSF and serum (). Follow-up CSF titres were not obtained in most patients after improvement.
To assess the effect of patients’ antibodies on neuronal cultures, we first determined the extent of immunolabelling of NR1 (or NMDA receptor) clusters in postsynaptic dendrites. Patients’ antibodies labelled nearly all clusters of NMDA receptors (). This antibody binding did not cause apoptosis (data not shown). However, adding patients’ IgG to rat hippocampal neuronal cultures produced a concentration-dependent decrease of the cell-surface fraction of NMDA receptors (). IgG from patients with high antibody titres produced a greater decrease of NMDA receptors than IgG from patients with low antibody titres (data not shown).
Immunolabelling of neuronal NR1 clusters
Effect of antibodies on the number of NMDA-receptor clusters in live neurons
The effect of patients’ antibodies on clusters of NMDA receptors in postsynaptic dendrites was quantified by confocal microscopy. Neurons treated with patients’ CSF for 3 days or 7 days had fewer clusters of NMDA receptors per length of postsynaptic dendrite than neurons treated with control CSF. By contrast, neurons treated for 3 days with patients’ CSF followed by 4 days with control CSF had similar numbers of clusters of NMDA receptors to those in neurons treated only with control CSF (). Patients’ antibodies did not change the concentrations of the postsynaptic protein PSD-95 (). Together, these findings show that patients’ antibodies produce a selective and reversible decrease of NMDA-receptor clusters in postsynaptic dendrites.