Pediatric Autoimmune Encephalitis
Autoimmune encephalitis in children encompasses a spectrum of immune-mediated conditions characterized by impaired alertness, often accompanied by seizures, movement disorders, and psychiatric features. Neuroimmune conditions in pediatrics typically manifest in previously healthy, normally developing children with abrupt onset, sometimes preceded by a viral prodrome. The recognition that many childhood encephalitic illnesses are antibody-mediated — and therefore treatable — has transformed the approach to acute neurologic deterioration in children. The most common antibodies identified in pediatric autoimmune encephalitis are directed against the NMDA receptor and myelin oligodendrocyte glycoprotein (MOG), though a substantial proportion remain seronegative.
Bottom Line
- Onset: Typically abrupt in previously healthy, normally developing children; may follow a viral prodrome
- Most common antibodies in children: NMDA receptor and MOG; a significant proportion are seronegative
- Essential workup for ALL patients: Serum + CSF antibody testing, brain + spine MRI with contrast, paired oligoclonal bands (OCBs)
- Normal EEG in a symptomatic child is a red flag suggesting an alternative, non-inflammatory diagnosis
- Antibody alone does not equal diagnosis: Clinical phenotype must match the antibody-associated syndrome
- Cell-surface antibodies (e.g., NMDA-R, LGI1) are more likely pathogenic and respond more favorably to immunotherapy than intracellular antibodies (e.g., GAD, Hu)
- Pediatric NMDA-R encephalitis: Complete recovery in 75% of children; recovery may take up to 18 months
- Early rituximab (within 4 weeks) associated with significantly better outcomes in pediatric NMDA-R encephalitis
Overview of Pediatric Neuroimmune Disorders
Pediatric neuroimmune conditions can be categorized into three broad groups based on their clinical course:
- Monophasic: Single episode, often postinfectious or postvaccination (e.g., acute disseminated encephalomyelitis [ADEM], most cases of pediatric NMDA-R encephalitis)
- Relapsing: Recurrent discrete episodes with recovery between attacks (e.g., NMOSD, MOGAD with relapses)
- Chronic neuroinflammation: Progressive or persistent inflammation (e.g., chronic lymphocytic inflammation with pontine perivascular enhancement responsive to steroids [CLIPPERS])
Historically, these conditions were divided into white matter (demyelinating) and gray matter (encephalitis) categories, but significant clinical overlap exists. In a small proportion of children presenting with apparent autoimmune neurologic disease, monogenetic disorders may cause autoinflammation, mimicking acquired autoimmune conditions.
Antibody Pathogenicity
The distinction between antibody types has important therapeutic implications:
- Cell-surface antigen antibodies (e.g., NMDA-R, LGI1, CASPR2, AQP4, MOG): More likely to be directly pathogenic; tend to respond more favorably to immunomodulatory therapy, particularly B cell–depleting agents
- Intracellular antigen antibodies (e.g., GAD, Hu, Yo, CV2): Serve primarily as biomarkers; T cell–mediated cytotoxicity is the main pathologic mechanism; generally less responsive to immunotherapy
Antibody Testing Considerations
- Both serum and CSF should always be tested
- Cell-based assays (CBA) are the preferred testing method for neuronal surface antibodies
- Live cell-based assays (available in research laboratories) offer higher sensitivity and specificity
- Fixed cell-based assays (commercial laboratories) provide faster turnaround and easier accessibility but have lower sensitivity and specificity
- Do NOT use antibody positivity alone for diagnosis, particularly if the clinical phenotype differs from the adult-reported syndrome
Diagnostic Pitfalls in Pediatric Autoimmune Encephalitis
- A normal EEG in a child with active encephalopathy should prompt reconsideration of the diagnosis — inflammatory encephalitis usually produces EEG abnormalities during symptomatic periods
- Antibody positivity without a matching clinical phenotype does not confirm autoimmune encephalitis
- Response to steroids is NOT specific to autoimmune conditions — steroids may temporarily improve symptoms in genetic epilepsies, mitochondrial disorders, and other non-immune conditions
- Always consider genetic mimics: ATP1A3 mutations (alternating hemiplegia), focal cortical dysplasia (explosive-onset epilepsies), and mitochondrial disorders
Antibody-Associated Syndromes in Children
| Antibody | Main Adult Phenotypes | Pediatric Phenotypes | Disease Course in Children |
|---|---|---|---|
| NMDA-R | Psychiatric symptoms, seizures, movement disorder, dysautonomia, hypoventilation | Movement disorders more prominent (prepubertal); neuropsychiatric features (postpubertal); post-HSV relapse | Typically monophasic; 12% relapse rate; 75% complete recovery |
| AQP4 | NMOSD: optic neuritis, longitudinally extensive transverse myelitis, area postrema syndrome | Similar to adults; optic neuritis and myelitis; brainstem involvement | Relapsing; requires long-term immunosuppression |
| MOG | ADEM-like, optic neuritis, myelitis, cortical encephalitis | ADEM (especially <6 years), bilateral optic neuritis, seizures, encephalopathy; most common antibody in pediatric demyelination | Frequently monophasic in young children; relapsing in older children |
| GFAP | Meningoencephalomyelitis, perivascular radial linear enhancement on MRI | Encephalopathy with meningeal signs; optic disc edema | Steroid-responsive; may relapse |
| LGI1 | Limbic encephalitis, faciobrachial dystonic seizures, hyponatremia | Very rare in children; limbic encephalitis phenotype when present | Limited pediatric data |
| CASPR2 | Morvan syndrome, limbic encephalitis, neuromyotonia | Extremely rare in children | Limited pediatric data |
| GlyR | Stiff-person spectrum, progressive encephalomyelitis with rigidity and myoclonus (PERM) | Stiff-person phenotype; may overlap with opsoclonus-myoclonus | Variable; steroid-responsive |
| GABAB | Limbic encephalitis, seizures; association with SCLC | Rare in children; seizures and encephalopathy | Limited pediatric data; not tumor-associated in children |
| GABAA | Refractory status epilepticus, encephalitis with multifocal cortical/subcortical MRI lesions | Status epilepticus, severe encephalopathy; cortical/subcortical MRI changes | Often severe; immunotherapy-responsive |
| DPPX | Encephalitis with gastrointestinal dysfunction (diarrhea, weight loss), hyperekplexia | Very rare in children | Limited pediatric data |
| mGluR1 | Cerebellar ataxia | Very rare in children; cerebellar phenotype | Limited pediatric data |
| mGluR2 | Cerebellar ataxia | Extremely rare in children | Limited pediatric data |
| AMPA | Limbic encephalitis; tumor association (thymoma, lung, breast) | Very rare in children | Limited pediatric data |
| GAD | Stiff-person syndrome, cerebellar ataxia, limbic encephalitis, epilepsy | Autoimmune epilepsy; overlap with type 1 diabetes; intracellular target — antibody is a biomarker | Chronic; less responsive to immunotherapy than cell-surface antibody conditions |
Pediatric NMDA Receptor Encephalitis
Anti-NMDA receptor encephalitis is the most common neuronal antibody-mediated condition in children, with approximately 40% of all NMDA-R encephalitis patients being under 18 years of age. Both serum and CSF should be tested, with CSF demonstrating higher diagnostic sensitivity.
Clinical Features
Pediatric NMDA-R encephalitis presents as a severe polysymptomatic encephalopathic syndrome with psychiatric symptoms, movement disorders, seizures, and dysautonomia. The clinical presentation differs by developmental stage:
| Feature | Prepubertal Children | Postpubertal Adolescents |
|---|---|---|
| Predominant presentation | More florid movement disorders | More prominent neuropsychiatric features |
| Ovarian teratoma | Rarely seen | Present in ~50% of females |
| Tumor type | 96% of reported tumors are teratomas | |
Investigations
- MRI: Frequently normal — a clinical-radiologic paradox in which critically ill children have unremarkable brain imaging
- EEG: Generalized rhythmic delta activity ± epileptic discharges; extreme delta brush pattern can be seen
- CSF: Oligoclonal bands frequently positive but may be negative early in the disease course
- Antibody titers: Some correlation with clinical state, but the utility of serial monitoring remains unclear; high titers may persist despite clinical recovery; rising titers with recurrent symptoms suggest relapse
Key Clinical Counseling Points
- Even with early initiation of immunotherapy, symptoms typically worsen over the first few weeks before improvement begins — families must be prepared for this trajectory
- Recovery occurs in reverse order of symptom onset and may take up to 18 months
- Neuropsychologic assessment is recommended as subtle cognitive sequelae are common even in “recovered” patients
Symptomatic Management
- Long-acting benzodiazepines for agitation and movement disorders
- Antiseizure medications (ASMs) for seizures
- Clonidine for dysautonomia and agitation
- Symptomatic treatment is rarely fully effective in the acute phase
Antipsychotic Use in NMDA-R Encephalitis
- Medication-related adverse effects are more common in patients with NMDA-R encephalitis than in those with primary psychiatric disorders
- Neuroleptic malignant syndrome, severe dystonia, and prolonged sedation have been reported
- If antipsychotics are required, use the lowest effective dose with close monitoring
Immunotherapy
First-Line Treatment
- IV methylprednisolone (IVMP): Standard pulse dosing
- IVIg: Standard dosing (0.4 g/kg/day × 5 days)
- Plasma exchange: Often limited to ICU settings; risk-benefit ratio must be carefully considered in children, particularly given procedural challenges in younger patients
- These agents may be used alone or in combination
Second-Line and Escalation Therapy
- Rituximab: 750 mg/m² × 2 doses, given 2 weeks apart
- Cyclophosphamide: Used alone or in combination with rituximab
- Many centers now use rituximab as first-line therapy, given mounting evidence for benefit with early administration
Evidence for Early Rituximab
- Multicenter study data demonstrate that early rituximab (within 4 weeks of symptom onset) is associated with 89% of patients achieving mRS <2
- When rituximab was given after 4 weeks, only 57% achieved mRS <2
- Pediatric NMDA-R encephalitis is typically monophasic — one course of rituximab is usually sufficient
- If inflammatory disease remains active when B cells repopulate (typically 4–6 months): consider a second course of rituximab
Maintenance Therapy
- For persistent or prolonged disease activity: azathioprine, mycophenolate mofetil, or tocilizumab
- Duration is individualized based on clinical course and antibody status
Outcomes
| Outcome Measure | Detail |
|---|---|
| Complete recovery | 75% of children |
| Recovery timeline | Up to 18 months; occurs in reverse order of symptom onset |
| Relapse rate | 12%; relapses often less severe than initial presentation |
| Cognitive sequelae | Subtle deficits common; neuropsychologic assessment recommended for all patients |
Atypical Presentations
Not all pediatric NMDA-R encephalitis presents with the full polysymptomatic syndrome. Clinicians should be aware of the following atypical presentations:
- Milder or incomplete phenotypes: May occur at initial presentation or at relapse
- Predominantly movement disorders with only milder cognitive features
- Monosymptomatic presentation: Occurs in <1% of cases; the clinical relevance of the antibody in isolated symptoms remains uncertain
Post-HSV NMDA-R Encephalitis
NMDA-R Antibodies Following HSV Encephalitis
- NMDA-R antibodies develop in approximately 50% of children who experience a clinical relapse ~1 month after HSV encephalitis
- Clinical features of relapse: Movement disorder, worsening encephalopathy, cognitive decline
- MRI: May show new bilateral white matter changes distinct from the original HSV lesions
- HSV PCR is negative at the time of relapse, confirming an immune-mediated rather than infectious mechanism
- Treatment: Identical to typical NMDA-R encephalitis (immunotherapy, not antivirals)
- Outcome: Worse than NMDA-R encephalitis without preceding HSV, especially in children under 2 years of age
Limbic Encephalitis in Children
Limbic encephalitis represents a distinct phenotype defined by medial temporal lobe abnormalities on MRI (unilateral, bilateral, or asymmetric), which are required for diagnosis. While limbic encephalitis in adults is often paraneoplastic (associated with small cell lung cancer) or antibody-positive (LGI1, CASPR2), the pediatric presentation differs significantly.
Key Features Distinguishing Pediatric from Adult Limbic Encephalitis
| Feature | Adult Limbic Encephalitis | Pediatric Limbic Encephalitis |
|---|---|---|
| Antibody status | Often LGI1, CASPR2, or paraneoplastic (Hu, CV2) | Typically seronegative |
| Tumor association | Frequent (SCLC, thymoma) | Not associated with tumors |
| Encephalopathy severity | Variable | Less severe than NMDA-R encephalitis |
| Memory impairment | Prominent | Retrograde and anterograde; takes weeks to months to resolve; may not be obvious unless formally tested |
| CSF | Often abnormal | Often unremarkable |
| Disease course | Variable; depends on antibody and tumor | Typically monophasic |
Extralimbic Involvement
Approximately 20% of children with limbic encephalitis demonstrate extralimbic involvement on imaging, termed “limbic encephalitis plus.” The claustrum is the most commonly affected extralimbic structure.
Treatment and Outcomes
- Corticosteroids are effective as first-line therapy
- Rituximab is beneficial even in seronegative cases
- The disease is typically monophasic, but a proportion of children develop postencephalitis epilepsy and temporal lobe atrophy over time
Late Worsening After Limbic Encephalitis
- If seizures or cognition worsen months to years after the initial episode, the pathobiology may differ from the original immune-mediated process
- Late deterioration may reflect gliotic scarring rather than ongoing chronic inflammation
- Consider referral for specialist complex epilepsy evaluation and possible epilepsy surgery rather than escalating immunotherapy
Seronegative Autoimmune Encephalitis
Seronegative autoimmune encephalitis — in which no known CNS antibody is identified and the presentation does not fulfill limbic encephalitis criteria — represents one of the most challenging diagnostic categories in pediatric neuroimmunology. These children typically present with a polysymptomatic encephalitis that is less severe than NMDA-R encephalitis.
Diagnostic Features
- No known CNS antibody identified on standard panels
- Does not fulfill criteria for limbic encephalitis (no characteristic MRI findings)
- EEG: Shows features of encephalopathy (generalized slowing, disorganization)
- CSF: Oligoclonal bands may be present but are not always found
- MRI: Typically normal
Treatment
- Treated similarly to NMDA-R encephalitis: corticosteroids + rituximab
- Other etiologies must be excluded in parallel with empiric immunotherapy
Genetic Mimics to Consider
- ATP1A3 mutations: Alternating hemiplegia of childhood, rapid-onset dystonia-parkinsonism — may present acutely and mimic autoimmune encephalitis
- Focal cortical dysplasia: May cause explosive-onset epilepsies that simulate autoimmune seizures
- Mitochondrial disorders: Can present with acute encephalopathy and may transiently respond to steroids
- Genetic epilepsies: Various channelopathies and other genetic epilepsy syndromes can present with acute encephalopathy
- Steroid responsiveness alone does NOT confirm an autoimmune etiology
Opsoclonus-Myoclonus Syndrome
Opsoclonus-myoclonus syndrome (OMS) is more common in children than adults, with a median onset age of 18 months. It is characterized by the triad of opsoclonus (chaotic, conjugate, multidirectional saccadic eye movements), myoclonus, and ataxia, often accompanied by prominent irritability and sleep disturbance.
Clinical Features and Tumor Association
- Core features: Opsoclonus + myoclonus + ataxia + irritability + sleep disturbance
- 50% are associated with neuroblastoma — tumor screening is mandatory in all children
- Non-neuroblastoma presentations are likely postinfectious in etiology
- Risk of neuroblastoma is lower in children >10 years; neuroblastoma-associated OMS is rare above this age
- Brain MRI is characteristically normal
Mandatory Tumor Screening in OMS
- Whole-body MRI: Required in all children with OMS to screen for neuroblastoma
- Urine catecholamines: Vanillylmandelic acid (VMA) and homovanillic acid (HVA) should be measured in all cases
- If initial screening is negative, repeat at intervals given the possibility of occult tumors
- ANNA-1 (anti-Hu) testing should be performed
Investigations
- CSF: Oligoclonal bands positive in approximately 50%, in both paraneoplastic and non-paraneoplastic cases
- CSF neopterins: May be elevated, reflecting CNS immune activation
- Brain MRI: Normal
Treatment
OMS is a chronic and relapsing condition that requires long-term immunosuppression. Relapses commonly occur with intercurrent illness or immunosuppression dose reduction.
| Treatment Line | Agent | Details |
|---|---|---|
| First-line | Dexamethasone pulses | 20 mg/m²/day for 3 days, given monthly for 1 year |
| Escalation | IVIg | Added if inadequate response to dexamethasone alone |
| Escalation | Rituximab | Recent shift toward early rituximab escalation |
| Escalation | Cyclophosphamide | For refractory cases |
Outcomes and Long-Term Sequelae
- Long-term cognitive impairment and behavioral problems occur in up to 75% of children
- Earlier and more aggressive immunotherapy may mitigate these sequelae
- Relapses are common with intercurrent infections and during immunosuppression tapering
- Long-term neurodevelopmental follow-up is essential
Diagnostic Approach to Pediatric Autoimmune Encephalitis
| Investigation | Rationale | Key Findings |
|---|---|---|
| Serum + CSF antibody panel | Identify treatable antibody-mediated conditions | NMDA-R, MOG, AQP4, LGI1, CASPR2, GABAA, GABAB, GAD, AMPA |
| Brain + spine MRI with contrast | Identify inflammatory changes; exclude structural and neoplastic conditions | Medial temporal signal (limbic); normal (NMDA-R); demyelination (MOG/AQP4) |
| Paired OCBs (CSF + serum) | Evidence of intrathecal antibody synthesis | Unpaired OCBs support CNS inflammation |
| EEG | Confirm encephalopathy; identify subclinical seizures | Normal EEG in symptomatic child = red flag for non-inflammatory etiology |
| Tumor screening | Identify paraneoplastic etiologies | Ovarian teratoma (NMDA-R); neuroblastoma (OMS); imaging + urine catecholamines |
| Infectious workup | Exclude or identify preceding infection | HSV PCR (especially if post-HSV NMDA-R suspected); viral panels |
| Genetic testing | Exclude mimics in seronegative or atypical cases | ATP1A3, mitochondrial gene panels, epilepsy gene panels |
Treatment Principles
General Treatment Approach in Pediatric Autoimmune Encephalitis
- First-line: IV methylprednisolone, IVIg, and/or plasma exchange (alone or combined)
- Second-line: Rituximab and/or cyclophosphamide
- Trend toward early rituximab in pediatric NMDA-R encephalitis, given evidence for superior outcomes with early administration
- Plasma exchange: Typically reserved for ICU patients; procedural considerations are important in children
- Maintenance options: Azathioprine, mycophenolate mofetil, tocilizumab for chronic or relapsing conditions
- Tumor removal: Essential when a tumor is identified (teratoma, neuroblastoma) — accelerates recovery and reduces relapse risk
- Symptomatic treatment: ASMs for seizures, benzodiazepines and clonidine for movement disorders and dysautonomia
Summary of Key Pediatric Autoimmune Encephalitis Syndromes
| Syndrome | Key Features | MRI | Antibody | Course | Treatment |
|---|---|---|---|---|---|
| NMDA-R encephalitis | Polysymptomatic: psychiatric, movement disorder, seizures, dysautonomia | Often normal | NMDA-R (serum + CSF) | Monophasic (88%) | Steroids, IVIg, rituximab (early) |
| Limbic encephalitis | Memory impairment, seizures, behavioral change | Medial temporal lobe abnormalities (required) | Usually seronegative in children | Monophasic; risk of postencephalitis epilepsy | Steroids, rituximab |
| Seronegative AE | Polysymptomatic but less severe than NMDA-R | Usually normal | Negative | Variable | Steroids, rituximab; exclude mimics |
| OMS | Opsoclonus, myoclonus, ataxia, irritability | Normal | No specific antibody; check ANNA-1 | Chronic, relapsing | Dexamethasone pulses, IVIg, rituximab |
References
- Hacohen Y. Pediatric autoimmune neurologic disorders. Continuum (Minneap Minn). 2024;30(4):1160-1188.
- de Bruijn MAAM, Aarsen FK, van Lier NAMB, et al. Long-term neuropsychological outcome following pediatric anti-NMDAR encephalitis. Neurology. 2018;90(22):e1997-e2005.
- Graus F, Titulaer MJ, Balu R, et al. A clinical approach to diagnosis of autoimmune encephalitis. Lancet Neurol. 2016;15(4):391-404.