NMOSD & MOGAD

Neuromyelitis Optica Spectrum Disorder

What You'll Learn

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

HighYield Pearls

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

🔍 Quick ReferenceClinical · 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.

🔒

Continue reading — sign in

The full note has more clinical pearls, tables, and board-focused tips. Free account, no fee.