NMOSD & MOGAD
Neuromyelitis Optica Spectrum Disorder
What Do You Need to Know?
- AQP4-IgG — most specific biomarker for NMOSD; targets aquaporin-4 on astrocyte foot processes → complement-mediated astrocytopathy (NOT primary demyelination like MS)
- NMOSD ≠ MS — longitudinally extensive transverse myelitis (≥3 segments), bilateral/severe optic neuritis, CSF OCBs rare (~10–20%), brain MRI often normal early; MS DMTs (interferon, fingolimod, natalizumab) WORSEN NMOSD
- IPND 2015 criteria — AQP4-IgG positive: 1 core clinical feature is sufficient; AQP4-IgG negative: requires ≥2 core features + dissemination in space + additional MRI requirements
- Six core clinical characteristics — optic neuritis, acute myelitis, area postrema syndrome (intractable hiccups/vomiting), acute brainstem syndrome, acute diencephalic syndrome, symptomatic cerebral syndrome
- MOG antibody disease (MOGAD) — distinct entity from AQP4-NMOSD and MS; bilateral anterior optic neuritis, ADEM-like brain lesions, conus myelitis; often steroid-responsive, with relapses that may occur during rapid taper (especially in relapsing adult disease — many children are monophasic); better overall prognosis than AQP4-NMOSD
- Acute treatment — high-dose IV methylprednisolone → PLEX (especially in AQP4+ patients); early PLEX improves outcomes
- Maintenance therapy — four FDA-approved agents for AQP4-IgG+ NMOSD: eculizumab (anti-C5), ravulizumab (anti-C5, long-acting q8 weeks; FDA-approved 2024 per CHAMPION-NMOSD), inebilizumab (anti-CD19), satralizumab (anti-IL-6R); rituximab widely used off-label
🚩 Don’t Miss — Test-Day Priorities
- AQP4-IgG (cell-based assay) = NMOSD: complement-mediated astrocytopathy targeting aquaporin-4 on astrocyte foot processes — NOT a primary demyelinating disease like MS
- LETM ≥3 contiguous vertebral segments + central cord (H-sign): hallmark of NMOSD myelitis; MS gives short-segment (<3) dorsolateral lesions
- Area postrema syndrome (intractable hiccups/vomiting): highly specific for NMOSD; may precede ON/myelitis by months → test AQP4-IgG
- Bilateral, severe ON with poor recovery + posterior nerve/chiasm involvement: NMOSD pattern; unilateral retrobulbar with good recovery = MS
- NEVER give MS DMTs in NMOSD: interferon-β, fingolimod, and natalizumab can trigger severe relapses — classic board trap
- Acute attack: high-dose IV methylprednisolone → early PLEX (within 5 days; do not wait for AQP4-IgG result); PLEX directly removes pathogenic antibody and complement
- Four FDA-approved AQP4+ NMOSD maintenance agents: eculizumab & ravulizumab (anti-C5), inebilizumab (anti-CD19, depletes plasmablasts rituximab misses), satralizumab (anti-IL-6R); eculizumab/ravulizumab: vaccinate with MenACWY and MenB ≥2 weeks before start when possible; if urgent treatment must precede full vaccination, add antibacterial prophylaxis until vaccination is complete — vaccination does not eliminate meningococcal risk
- MOGAD is a distinct disease, NOT “seronegative NMOSD”: MOG-IgG by cell-based assay (NOT ELISA); papillitis + perineural/sheath enhancement on ON MRI; FLAMES (cortical encephalitis with seizures) is MOGAD-specific
- MOGAD is highly steroid-responsive but relapses on rapid taper: taper slowly over 3–6 months; maintenance options (relapsing disease) include IVIG monthly, rituximab, MMF, AZA — no FDA-approved agents
- Pediatric NMO-phenotype: test BOTH AQP4-IgG and MOG-IgG — MOGAD is MORE common than AQP4-NMOSD in children and often monophasic
🔍 Buzzwords & Pathognomonic FindingsClinical · MRI · Antibody / pathology
Clinical phenotype
- Intractable hiccups, nausea, or vomiting → area postrema syndrome (AQP4-NMOSD)
- Bilateral simultaneous severe optic neuritis with poor recovery → AQP4-NMOSD
- Paroxysmal painful tonic spasms after attack recovery → NMOSD (residual cord injury)
- Symptomatic narcolepsy / SIADH / hypothermia (diencephalic syndrome) → AQP4-NMOSD
- ADEM-like presentation in a child with optic neuritis → MOGAD
- Optic neuritis with painful orbital pain on eye movement + disc edema (papillitis) → MOGAD
- Seizures + cortical encephalitis (FLAMES) → MOGAD cortical encephalitis variant
MRI signs
- LETM ≥3 contiguous vertebral segments + central cord (“H-sign”/“owl’s eye”) → AQP4-NMOSD (also MOGAD)
- Bright spotty cord lesions on T2 → AQP4-NMOSD
- Dorsal medulla / floor of 4th ventricle (area postrema) lesion → AQP4-NMOSD
- Periependymal “pencil-thin” rim lesions around 3rd/lateral ventricles → AQP4-NMOSD
- Bilateral hypothalamic / diencephalic involvement → AQP4-NMOSD
- Callosal “marbled” or “arch-bridge” pattern → AQP4-NMOSD (vs MS Dawson fingers)
- Perineural/optic-nerve-sheath enhancement on ON MRI → MOGAD
- Posterior optic nerve and/or chiasm involvement, >½ nerve length → AQP4-NMOSD
- Conus medullaris involvement in myelitis → MOGAD
- Fluffy, ill-defined deep gray/white matter ADEM-like lesions → MOGAD
- Unilateral/bilateral cortical FLAIR hyperintensity + leptomeningeal enhancement → MOGAD (FLAMES)
Antibody / pathology / treatment
- AQP4-IgG by cell-based assay (sensitivity ~76%, specificity >99%) → NMOSD
- MOG-IgG by live cell-based assay (ELISA/Western NOT recommended) → MOGAD
- Perivascular complement + IgG + neutrophil/eosinophil infiltrate on biopsy → AQP4-NMOSD (rim-and-rosette / vasculocentric)
- CSF OCBs rare (~10–20%); neutrophilic/mixed pleocytosis → NMOSD (vs ~90–95% OCB+ in MS)
- Eculizumab / ravulizumab (anti-C5) requires MenACWY + MenB vaccination ≥2 weeks before start (antibacterial prophylaxis if urgent treatment precedes full vaccination) → AQP4-NMOSD maintenance
- Inebilizumab (anti-CD19) depletes plasmablasts that rituximab (anti-CD20) misses → AQP4-NMOSD maintenance
- Satralizumab (anti-IL-6R, SC q4 weeks) → AQP4-IgG+ NMOSD only (seronegative subgroup did not benefit)
- AVOID interferon-β, fingolimod, natalizumab → they WORSEN NMOSD (classic board trap)
- Highly steroid-responsive, relapse on rapid taper, monthly IVIG for prevention → MOGAD
- Early PLEX (within 5 days) as first/second step in severe attacks → AQP4-NMOSD
Pathophysiology & AQP4-IgG
Aquaporin-4 & Astrocyte Targeting
- Aquaporin-4 (AQP4): the most abundant water channel in the CNS; concentrated at astrocyte foot processes at the blood–brain barrier, ependymal surfaces, and pia mater
- AQP4-IgG (NMO-IgG): pathogenic IgG1 autoantibody that binds AQP4 on astrocyte endfeet → activates classical complement cascade → complement-dependent cytotoxicity (CDC) → astrocyte destruction
- Astrocytopathy, NOT demyelination: primary target is the astrocyte (not myelin or oligodendrocyte); demyelination occurs secondarily after astrocyte loss
- AQP4-rich regions: optic nerves, spinal cord (especially central gray matter), area postrema (dorsal medulla), periependymal regions, hypothalamus — explains the clinical phenotype
- Complement activation: AQP4-IgG is predominantly IgG1 subclass → potent complement activator → C5b-9 membrane attack complex (MAC) formation on astrocytes → rationale for eculizumab (anti-C5)
- Role of IL-6: promotes plasmablast survival and AQP4-IgG production; elevated in CSF during NMOSD attacks → rationale for satralizumab (anti-IL-6R)
💎 Board Pearl
- NMOSD is a complement-mediated astrocytopathy, NOT a primary demyelinating disease. AQP4-IgG (IgG1) binds astrocyte foot processes → activates complement → astrocyte destruction → secondary demyelination. This is fundamentally different from MS (T-cell mediated oligodendrocyte/myelin attack).
- AQP4-IgG is the most specific biomarker for NMOSD — cell-based assay sensitivity ~76%, specificity >99%. Seronegative patients may harbor MOG-IgG or have a different disorder altogether.
Diagnostic Criteria (IPND 2015)
Six Core Clinical Characteristics
| # | Core Feature | Key Details |
|---|---|---|
| 1 | Optic neuritis | Bilateral simultaneous or sequential; severe visual loss; poor recovery; often posterior optic nerve and/or chiasm involvement. IPND 2015 MRI requirement: ON-lesion extending >½ optic nerve length OR involving the chiasm |
| 2 | Acute myelitis | Severe motor/sensory deficits; central cord/gray matter predominant. IPND 2015 MRI requirement (mandatory in seronegative cases): LETM — T2 lesion spanning ≥3 contiguous vertebral segments |
| 3 | Area postrema syndrome | Intractable hiccups, nausea, or vomiting (otherwise unexplained); dorsal medulla lesion; often earliest/presenting feature |
| 4 | Acute brainstem syndrome | Periependymal brainstem lesions; may cause cranial nerve palsies, vertigo, hearing loss |
| 5 | Acute diencephalic syndrome | Symptomatic narcolepsy or acute diencephalic syndrome with NMOSD-typical diencephalic MRI lesion (SIADH/hypothermia are supportive features, not required for this core criterion) |
| 6 | Symptomatic cerebral syndrome | Large hemispheric lesions (often tumefactive) with NMOSD-typical brain MRI lesions; periependymal white matter pattern (distinct from MS) |
IPND 2015 Criteria — AQP4-IgG Positive vs Negative
| Criterion | AQP4-IgG Seropositive | AQP4-IgG Seronegative (or Unknown Status) |
|---|---|---|
| Core features required | ≥1 core clinical characteristic | ≥2 different core clinical characteristics (from ≥1 clinical attack) |
| Dissemination in space (DIS) | Not required | Required — ≥2 different core clinical characteristics |
| Required “anchor” core feature | Not required | At least one of the core features must be optic neuritis, acute myelitis with LETM, or area postrema syndrome |
| Additional MRI requirements | Not required | Fulfillment of additional MRI requirements as applicable to each core feature (e.g., LETM for myelitis, area postrema lesion for hiccups/vomiting, ON-lesion >½ nerve length or chiasm for ON) |
| Exclusion of alternative diagnoses | Required | Required |
| Antibody testing | Positive (cell-based assay preferred) | Tested and negative (or unavailable); must also exclude MS and MOGAD |
💎 Board Pearl
- AQP4-IgG positive + 1 core feature = NMOSD diagnosis. Seronegative patients need ≥2 core features + DIS + stringent MRI requirements. Always use cell-based assay (CBA) — significantly more sensitive than older ELISA-based testing.
- Area postrema syndrome (intractable hiccups/vomiting) is highly specific for NMOSD and may be the presenting symptom months before optic neuritis or myelitis develops. Any patient with unexplained intractable hiccups or vomiting should be tested for AQP4-IgG.
NMOSD vs MS — Critical Comparison
Head-to-Head Comparison
| Feature | NMOSD (AQP4+) | MS |
|---|---|---|
| Pathogenesis | Humoral (antibody + complement) → astrocytopathy | T-cell mediated → demyelination |
| Biomarker | AQP4-IgG positive | No specific antibody; OCBs in CSF (~95%) |
| Optic neuritis | Bilateral, severe, poor recovery; often posterior optic nerve and/or chiasm involvement | Unilateral, milder, good recovery; anterior/retrobulbar |
| Transverse myelitis | LETM ≥3 vertebral segments; central cord (gray matter predominant) | Short-segment TM (<3 segments); peripheral/dorsolateral (white matter) |
| Brain MRI (early) | Often normal or non-specific; area postrema, periependymal, hypothalamic lesions | Periventricular Dawson fingers, juxtacortical, infratentorial lesions |
| Spinal cord MRI | LETM; bright spotty lesions (T2 hyperintense); central/H-shaped on axial | Short lesions; dorsolateral; peripheral location |
| CSF OCBs | Rare (~10–20%) | Common (~90–95%) |
| CSF pleocytosis | Neutrophilic or mixed; can be >50 cells | Lymphocytic; usually <50 cells |
| Female:Male ratio | 9:1 | 3:1 |
| Racial predilection | Non-white predominance (African, Asian, Hispanic) | Northern European / Caucasian predominance |
| Disease course | Relapsing in >90%; progressive course extremely rare | RRMS → SPMS in ~50%; PPMS in ~15% |
| Attack severity | Severe, often devastating; poor recovery | Generally milder per attack; cumulative disability |
| Treatment | Eculizumab, inebilizumab, satralizumab, rituximab | Interferons, glatiramer, natalizumab, fingolimod, ocrelizumab, etc. |
| MS DMTs in NMOSD | CONTRAINDICATED — interferon-beta, fingolimod, and natalizumab can all WORSEN NMOSD | |
💎 Board Pearl
- MS DMTs can WORSEN NMOSD. Interferon-beta, fingolimod, and natalizumab have all been reported to trigger severe NMOSD relapses. This is one of the most board-tested points — always confirm the correct diagnosis before starting treatment.
- LETM (≥3 segments) + central cord involvement = think NMOSD, not MS. MS causes short-segment (<3 segments), peripheral/dorsolateral cord lesions. If you see a long lesion spanning 3+ segments, test AQP4-IgG immediately.
- CSF OCBs are present in ~90–95% of MS but only ~10–20% of NMOSD. A negative OCB result in a patient with recurrent optic neuritis and myelitis should raise strong suspicion for NMOSD.
MRI Features
Spinal Cord MRI
- LETM (longitudinally extensive transverse myelitis): T2 hyperintense lesion spanning ≥3 contiguous vertebral segments — hallmark of NMOSD
- Location: central cord / gray matter predominant — “H-shaped” or “owl’s eye” pattern on axial imaging
- Bright spotty lesions: very hyperintense T2 signal foci within the cord lesion; relatively specific for NMOSD
- Gadolinium enhancement: ring or patchy enhancement during acute attacks; may persist for weeks
- Cervicothoracic predilection: lesions commonly extend from cervical to thoracic cord; may extend into medulla (continuous with area postrema lesion)
- Cord cavitation/atrophy: occurs in chronic phase after severe attacks
Brain MRI
| Lesion Pattern | Location | Significance |
|---|---|---|
| Area postrema / dorsal medulla | Floor of 4th ventricle | Highly specific for NMOSD; correlates with intractable hiccups/vomiting |
| Periependymal | Around lateral ventricles, 3rd ventricle, aqueduct | Follows AQP4-rich ependymal surfaces; may form “pencil-thin” periependymal rim lesions |
| Hypothalamic/diencephalic | Hypothalamus, thalamus | Narcolepsy, endocrine dysfunction, SIADH |
| Callosal lesions | Corpus callosum (marbled or arch-bridge pattern) | Follows callosal AQP4 distribution; differs from MS (Dawson fingers are perpendicular to ventricles) |
| Large hemispheric | Tumefactive white matter lesions | Can mimic tumors or ADEM; often periependymal extension |
| Corticospinal tract | Internal capsule, cerebral peduncle | Longitudinally extensive white matter tract involvement |
Optic Nerve MRI
- NMOSD: posterior optic nerve and/or optic chiasm involvement; bilateral; longitudinally extensive (>50% of nerve length)
- MS: anterior/retrobulbar optic nerve; typically unilateral; short-segment
- MOGAD: anterior optic nerve with perineural enhancement (sheath enhancement); bilateral; optic disc edema (papillitis) common
Clinical Pearl
- Optic nerve involvement pattern helps differentiate NMOSD vs MS vs MOGAD: posterior/chiasmal = NMOSD, anterior/retrobulbar = MS, anterior with perineural sheath enhancement = MOGAD. This is a high-yield imaging distinction for boards.
MOG Antibody Disease (MOGAD)
Overview
- MOG-IgG: autoantibody targeting myelin oligodendrocyte glycoprotein (MOG) on the outer surface of myelin sheath and oligodendrocyte surface
- Distinct entity from both AQP4-NMOSD and MS — different pathogenesis, clinical phenotype, MRI, treatment response, and prognosis
- Testing: live cell-based assay (CBA) preferred using cells expressing full-length human MOG; fixed CBA acceptable but with higher false-positive rate; ELISA and Western blot are NOT recommended
- Demographics: affects all ages; children and young adults predominant; no strong sex predominance (unlike AQP4-NMOSD)
2023 International MOGAD Diagnostic Criteria (Banwell et al.)
| # | Criterion | Details |
|---|---|---|
| 1 | Core clinical demyelinating event | Optic neuritis, myelitis, ADEM, cerebral monofocal/polyfocal deficits, brainstem/cerebellar syndrome, or cortical encephalitis (often with seizures) |
| 2 | MOG-IgG positivity by cell-based assay | Clear positive serum (typically titer >1:100) is diagnostic when paired with a core clinical event. If serum is low-positive, negative, or unavailable, supporting clinical and MRI features are required (e.g., bilateral simultaneous ON, perineural enhancement, ADEM-like lesions, cortical encephalitis pattern). CSF MOG-IgG testing may be useful in select cases (seronegative serum with high clinical suspicion) |
| 3 | Exclusion of better diagnoses | Rule out MS, AQP4-NMOSD, infectious/metabolic/neoplastic mimics |
MOGAD Clinical Phenotypes — Key Acronym
- FLAMES — FLAIR-hyperintense Lesions in Anti-MOG-associated Encephalitis with Seizures: a cortical encephalitis variant of MOGAD; unilateral or bilateral cortical FLAIR hyperintensity + seizures + headache ± leptomeningeal enhancement; highly steroid-responsive
Clinical Features
| Feature | Details |
|---|---|
| Optic neuritis | Most common presentation in adults; often longitudinally extensive (>50% of nerve length) with optic disc edema (papillitis) and perineural/sheath enhancement; bilateral common; good visual recovery typical |
| Myelitis | LETM common; conus medullaris involvement is characteristic; can also be short-segment (~30–40% of adult cases); central gray-matter involvement (“H-sign” on axial cord MRI) often seen — note this pattern is also a feature of cord infarction |
| ADEM | Most common presentation in children; large fluffy white matter lesions; often monophasic in children; deep gray matter involvement |
| Cortical encephalitis | Seizures + cortical FLAIR hyperintensity + leptomeningeal enhancement; relatively unique to MOGAD |
| Brainstem involvement | Less common; may cause cranial nerve palsies; area postrema involvement is less typical than in AQP4-NMOSD |
MOGAD vs AQP4-NMOSD vs MS
| Feature | MOGAD | AQP4-NMOSD | MS |
|---|---|---|---|
| Antibody | MOG-IgG | AQP4-IgG | None (OCBs in CSF) |
| Target | Myelin/oligodendrocyte (MOG) | Astrocyte (AQP4) | Myelin/oligodendrocyte |
| Pathology | Perivenous demyelination; complement deposition variable | Complement-mediated astrocytopathy | Perivenous and confluent demyelination; T-cell mediated |
| Optic neuritis | Often longitudinally extensive (>50% nerve); papillitis, perineural/sheath enhancement; bilateral common; good recovery | Bilateral; often posterior optic nerve and/or chiasm; poor recovery | Unilateral, retrobulbar; good recovery |
| Myelitis | LETM or short; conus/lower cord | LETM; cervicothoracic; central cord | Short-segment; dorsolateral |
| Brain lesions | ADEM-like (fluffy, deep gray); cortical FLAIR | Periependymal, area postrema, hypothalamic | Periventricular Dawson fingers, juxtacortical |
| CSF OCBs | Rare (<15%) | Rare (~10–20%) | Common (~90–95%) |
| Age of onset | Children and young adults | Middle-aged adults (median ~40) | Young adults (20–40) |
| Sex ratio (F:M) | ~1:1 (slight F predominance) | 9:1 | 3:1 |
| Course | Monophasic (children) or relapsing (adults) | Relapsing (>90%) | RRMS → SPMS; PPMS |
| Prognosis | Best; good attack recovery | Worst; severe disability with attacks | Variable; cumulative disability |
| Steroid response | Highly responsive; relapses on taper | Partial; often needs PLEX | Partial; speeds recovery |
| Maintenance therapy | For relapsing MOGAD, options include IVIG (monthly; strong observational support, especially for relapse prevention), rituximab, mycophenolate, azathioprine, and prolonged steroid taper. No FDA-approved agents; evidence is mostly observational | Eculizumab, ravulizumab, inebilizumab, satralizumab, rituximab | Multiple FDA-approved DMTs |
💎 Board Pearl
- MOGAD is a distinct disease — it is NOT “seronegative NMOSD.”
- Dual AQP4-IgG and MOG-IgG positivity is exceedingly rare; when reported, it usually reflects assay artifact and should prompt retesting on a validated cell-based assay before accepting both diagnoses.
- MOGAD is often steroid-responsive; relapses may occur during rapid taper (especially in relapsing adult disease — many children are monophasic). Taper slowly over 3–6 months rather than a typical short MS relapse taper.
- Optic nerve perineural enhancement (sheath enhancement) on MRI is relatively specific for MOGAD and helps distinguish it from AQP4-NMOSD and MS optic neuritis.
- Cortical encephalitis with seizures + cortical FLAIR signal is a MOGAD-specific phenotype not seen in AQP4-NMOSD or typical MS.
Treatment — Acute Attacks
Acute Attack Management
| Treatment | Regimen | Key Points |
|---|---|---|
| IV methylprednisolone | 1 g/day × 3–5 days | First-line for all NMOSD attacks; start immediately upon clinical suspicion; oral taper often follows |
| Plasma exchange (PLEX) | 5–7 exchanges over 10–14 days | Strongly recommended early in AQP4+ NMOSD; directly removes pathogenic AQP4-IgG and complement; consider as first-line (not just rescue) in severe attacks |
| IVIG | 2 g/kg over 2–5 days | Alternative when PLEX unavailable; less evidence in AQP4+ NMOSD than PLEX; may be useful in MOGAD |
- Early PLEX improves outcomes: studies show initiating PLEX within 5 days of symptom onset significantly improves recovery in AQP4+ patients
- Do NOT delay treatment while awaiting AQP4-IgG results — NMOSD attacks cause irreversible damage with each episode
- Steroid taper: oral prednisone taper over 2–6 months depending on severity and maintenance therapy status
Treatments That WORSEN NMOSD
| MS Drug | Mechanism of Harm in NMOSD |
|---|---|
| Interferon-beta | Upregulates BAFF/BLyS → increases B-cell survival and antibody production; reported to trigger severe NMOSD relapses |
| Fingolimod | Traps regulatory T cells in lymph nodes; does not prevent humoral immune response; associated with rebound NMOSD attacks |
| Natalizumab | Anti-VLA-4 does not address complement-mediated astrocytopathy; ineffective and may allow ongoing humoral attack |
| Alemtuzumab | Scattered case reports of worsening; not as strongly contraindicated as IFN-β, fingolimod, or natalizumab; secondary autoimmunity risk also a concern |
💎 Board Pearl
- PLEX is more effective than steroids alone in AQP4+ NMOSD acute attacks. Unlike MS (where steroids are first-line and PLEX is rescue), early PLEX should be strongly considered as first or second step in NMOSD — it directly removes the pathogenic antibody and complement.
- Board classic: a patient misdiagnosed with MS and started on interferon-beta who then develops a devastating NMOSD relapse. Always test AQP4-IgG before starting MS DMTs in patients with LETM or bilateral ON.
Treatment — Maintenance / Prevention
FDA-Approved Agents for AQP4-IgG+ NMOSD
| Drug | Target | Mechanism | Route / Dosing | Key Trial | Key Considerations |
|---|---|---|---|---|---|
| Eculizumab (Soliris) | C5 complement | Blocks terminal complement activation → prevents MAC (C5b-9) formation on astrocytes | IV infusion q2 weeks (after loading) | PREVENT | Vaccinate with MenACWY + MenB ≥2 weeks before starting when possible; if urgent treatment must precede full vaccination, add antibacterial prophylaxis until vaccination is complete. Vaccination does not eliminate meningococcal risk — counsel on prompt evaluation for any febrile illness; very expensive |
| Inebilizumab (Uplizna) | CD19 | Broader B-cell depletion than anti-CD20 — includes plasmablasts that produce AQP4-IgG | IV: days 1 & 15, then q6 months | N-MOmentum | HBV screening mandatory; infection monitoring; targets AQP4-IgG-producing cells more directly than rituximab |
| Satralizumab (Enspryng) | IL-6 receptor | Blocks IL-6 signaling → ↓ plasmablast survival and AQP4-IgG production | SC: weeks 0, 2, 4 (loading), then q4 weeks | SAkuraSky / SAkuraStar | Can be monotherapy or add-on; subcutaneous self-injection. Approved only for AQP4-IgG seropositive NMOSD; the SAkura trials did not show significant benefit in the seronegative subgroup |
| Ravulizumab (Ultomiris) | C5 complement | Long-acting C5 inhibitor — blocks terminal complement → prevents MAC formation on astrocytes | IV loading, then maintenance q8 weeks | CHAMPION-NMOSD | FDA-approved 2024 for AQP4-IgG+ NMOSD. Same meningococcal vaccination strategy as eculizumab (MenACWY + MenB ≥2 weeks before start, or antibacterial prophylaxis until vaccination is complete if treatment is urgent); less frequent dosing |
Off-Label / Older Maintenance Regimens
| Drug | Target / Mechanism | Notes |
|---|---|---|
| Rituximab | Anti-CD20 → B-cell depletion | Most widely used worldwide; IV q6 months; monitor CD19/CD20 counts and immunoglobulins; does NOT deplete plasmablasts (CD20-negative) |
| Azathioprine | Purine analog | Used in resource-limited settings; check TPMT; slow onset (3–6 months); bridge with oral steroids |
| Mycophenolate mofetil | IMPDH inhibitor | Alternative maintenance; teratogenic; GI side effects; also requires steroid bridge |
| Tocilizumab | Anti-IL-6 receptor (IV) | Off-label alternative to satralizumab; IV infusion q4 weeks; case series and small trials support efficacy |
Treatment Selection Considerations
- AQP4-IgG positive: all four FDA-approved agents (eculizumab, ravulizumab, inebilizumab, satralizumab) are indicated; choice depends on access, cost, route preference, dosing interval, and comorbidities
- AQP4-IgG negative NMOSD: no FDA-approved therapies; rituximab, azathioprine, or mycophenolate used empirically; consider MOGAD testing
- Eculizumab advantage: directly blocks the pathogenic mechanism (complement-mediated astrocytopathy); 94% relapse reduction in PREVENT trial
- Inebilizumab advantage over rituximab: depletes CD19+ cells including plasmablasts (CD20-negative but CD19+) that produce AQP4-IgG
- Never stop maintenance abruptly — NMOSD has a high relapse rate off therapy; each attack causes cumulative disability
💎 Board Pearl
- Know the four FDA-approved NMOSD drugs and their targets: eculizumab (anti-C5 complement), ravulizumab (anti-C5, long-acting; FDA 2024), inebilizumab (anti-CD19), satralizumab (anti-IL-6R). All are approved ONLY for AQP4-IgG seropositive NMOSD.
- Vaccinate with MenACWY and MenB ≥2 weeks before starting eculizumab or ravulizumab when possible; if urgent treatment must precede full vaccination, use antibacterial prophylaxis until vaccination is complete. Vaccination does not eliminate meningococcal risk — counsel on prompt evaluation for any febrile illness. Complement inhibition increases risk of encapsulated organism infections, especially Neisseria meningitidis.
- Inebilizumab (anti-CD19) depletes plasmablasts that rituximab (anti-CD20) cannot reach. Plasmablasts are CD20-negative but CD19-positive, and they produce AQP4-IgG. This is why inebilizumab may be more effective than rituximab in NMOSD.
Comprehensive Comparison — AQP4-NMOSD vs MOGAD vs MS
Master Comparison Table
| Feature | AQP4-NMOSD | MOGAD | MS |
|---|---|---|---|
| Autoantibody | AQP4-IgG | MOG-IgG | None (OCBs in ~95%) |
| Target cell | Astrocyte | Oligodendrocyte / myelin | Oligodendrocyte / myelin |
| Pathology | Complement-mediated astrocytopathy | Perivenous demyelination | Confluent demyelination (T-cell driven) |
| Sex ratio (F:M) | 9:1 | ~1:1 | 3:1 |
| Typical age | 30–50 | Children & young adults | 20–40 |
| Racial predilection | Non-white (African, Asian, Hispanic) | No strong predilection | Northern European / Caucasian |
| Optic neuritis | Often posterior optic nerve and/or chiasm; bilateral; severe; poor recovery | Often longitudinally extensive (>50% nerve); papillitis; perineural enhancement; bilateral common; good recovery | Retrobulbar; unilateral; mild; good recovery |
| Myelitis | LETM (≥3 segments); cervicothoracic; central gray matter | LETM or short; conus/lower cord | Short-segment (<3); dorsolateral white matter |
| Brain MRI | Periependymal, area postrema, hypothalamic, callosal (arch pattern) | ADEM-like (fluffy, deep gray matter); cortical FLAIR | Periventricular Dawson fingers; juxtacortical; infratentorial |
| Area postrema syndrome | Characteristic (intractable hiccups/vomiting) | Rare | Very rare |
| CSF OCBs | ~10–20% | <15% | ~90–95% |
| CSF profile | Neutrophilic/mixed pleocytosis; elevated protein | Lymphocytic/mixed; elevated protein | Mild lymphocytic pleocytosis; oligoclonal bands |
| Disease course | Relapsing (>90%); NO progressive form | Monophasic (children) or relapsing (adults) | RRMS → SPMS; PPMS |
| Attack severity | Severe; poor recovery; step-wise disability | Moderate; generally good recovery | Variable; cumulative |
| Acute treatment | IV steroids + early PLEX | IV steroids (highly responsive); slow taper | IV steroids; PLEX for refractory |
| Maintenance | Eculizumab, ravulizumab, inebilizumab, satralizumab, rituximab | IVIG (monthly; strong observational support, especially for relapse prevention), rituximab, MMF, AZA, prolonged steroid taper; no FDA-approved agents (evidence largely observational) | IFN-beta, GA, natalizumab, fingolimod, ocrelizumab, etc. |
| MS DMTs safe? | NO — can worsen disease (interferon-β, fingolimod, natalizumab) | Not indicated and not reliable for relapse prevention; confirm the diagnosis (MOG-IgG by CBA) before treating as MS | Yes — standard of care |
| Overall prognosis | Worst (severe cumulative disability) | Best (good recovery from attacks) | Variable (depends on phenotype and treatment) |
💎 Board Pearl
- The three diseases have different cellular targets: AQP4-NMOSD attacks astrocytes, MOGAD attacks oligodendrocytes/myelin, and MS attacks myelin via T-cells. Only AQP4-NMOSD is a complement-mediated astrocytopathy.
- Prognosis ranking: MOGAD (best recovery per attack) > MS (variable, cumulative) > AQP4-NMOSD (worst per-attack recovery, step-wise disability). Despite this, MOGAD can be relapsing and debilitating if not treated.
Special Topics & Board Pearls
Area Postrema Syndrome
- Presentation: intractable hiccups, nausea, and vomiting lasting days to weeks — not explained by GI workup
- Mechanism: AQP4 is highly expressed at the area postrema (dorsal medulla, floor of 4th ventricle), which lacks a blood–brain barrier
- Clinical significance: may be the first and only manifestation of NMOSD for months before optic neuritis or myelitis develops
- MRI: T2/FLAIR hyperintensity in the dorsal medulla / area postrema
- Board tip: unexplained intractable hiccups or vomiting → think NMOSD → order AQP4-IgG and brain MRI
Pregnancy & NMOSD
- Increased relapse risk in the postpartum period (similar to MS but often more severe)
- Azathioprine: generally considered safer in pregnancy than mycophenolate
- Mycophenolate mofetil: teratogenic (under REMS program); contraindicated in pregnancy; effective contraception required before, during, and for ≥6 weeks after discontinuation
- Rituximab: typically held during pregnancy; give at least 6 months before planned conception
- Eculizumab: moderate pregnancy experience from PNH/aHUS use; generally acceptable with risk-benefit discussion; IgG1 antibody that crosses the placenta, especially in the third trimester
- IVIG: considered safe in pregnancy; may be used for relapse prevention in high-risk patients
Pediatric NMOSD
- AQP4-IgG can be positive in children; clinical features similar to adults
- Important: MOGAD is MORE common than AQP4-NMOSD in children with NMO phenotype
- Test BOTH AQP4-IgG and MOG-IgG in any pediatric patient with a demyelinating/NMO-like presentation (ON, myelitis, ADEM, area postrema syndrome)
- Children with ADEM-like presentation should be tested for MOG-IgG
- Pediatric AQP4+ NMOSD has similar relapsing course and severity as adult disease
💎 Board Pearl
- Area postrema syndrome (intractable hiccups/vomiting) is the most specific clinical presentation for NMOSD. It is included as a core diagnostic feature in the IPND 2015 criteria. Patients are often initially evaluated by gastroenterology before the neurological diagnosis is made.
- In children with an NMO-like phenotype, test for MOG-IgG first — MOGAD is more common than AQP4-NMOSD in the pediatric population. MOG-IgG positive children often present with ADEM and have a better prognosis.
- NMOSD does NOT have a progressive phenotype. Unlike MS (which can be RRMS, SPMS, or PPMS), NMOSD causes disability through incomplete recovery from discrete relapses (step-wise worsening). If a patient appears to have “progressive NMOSD,” reconsider the diagnosis.
References
- Wingerchuk DM, Banwell B, Bennett JL, et al. International consensus diagnostic criteria for neuromyelitis optica spectrum disorders (IPND 2015). Neurology. 2015;85(2):177–189.
- Pittock SJ, Berthele A, Fujihara K, et al. Eculizumab in aquaporin-4-positive neuromyelitis optica spectrum disorder (PREVENT). N Engl J Med. 2019;381(7):614–625.
- Cree BAC, Bennett JL, Kim HJ, et al. Inebilizumab for the treatment of neuromyelitis optica spectrum disorder (N-MOmentum). Lancet. 2019;394(10206):1352–1363.
- Yamamura T, Kleiter I, Fujihara K, et al. Trial of satralizumab in neuromyelitis optica spectrum disorder (SAkuraStar). N Engl J Med. 2019;381(22):2114–2124.
- Traboulsee A, Greenberg BM, Bennett JL, et al. Safety and efficacy of satralizumab monotherapy in neuromyelitis optica spectrum disorder (SAkuraSky). Lancet Neurol. 2020;19(5):402–412.
- Banwell B, Bennett JL, Marignier R, et al. Diagnosis of myelin oligodendrocyte glycoprotein antibody-associated disease: International MOGAD Panel proposed criteria. Lancet Neurol. 2023;22(3):268–282.
- Lennon VA, Wingerchuk DM, Kryzer TJ, et al. A serum autoantibody marker of neuromyelitis optica: distinction from multiple sclerosis. Lancet. 2004;364(9451):2106–2112.
- Jarius S, Paul F, Weinshenker BG, et al. Neuromyelitis optica. Nat Rev Dis Primers. 2020;6(1):85.
- Bhatt A. Ultimate Review for the Neurology Boards. 3rd ed. Demos Medical; 2016.
- Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor’s Principles of Neurology. 12th ed. McGraw-Hill; 2023.
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