Nervous System & Special Senses

Neuromyelitis optica spectrum disorder

Clinical Overview and When to Suspect NMOSD

— Severe optic neuritis with profound visual loss, often bilateral or sequential, poor recovery

— Transverse myelitis with a spinal MRI lesion spanning ≥3 vertebral segments (LETM)

— Area postrema syndrome: intractable hiccups, nausea, vomiting lasting days–weeks

— Brainstem syndromes, symptomatic narcolepsy, or diencephalic syndromes

— Coexisting autoimmunity (SLE, Sjögren, myasthenia gravis, autoimmune thyroid disease)

Neuromyelitis optica spectrum disorder (NMOSD) is a relapsing autoimmune astrocytopathy of the CNS, classically defined by attacks of optic neuritis and longitudinally extensive transverse myelitis (LETM), mediated in most cases by IgG antibodies against the aquaporin-4 (AQP4) water channel on astrocyte foot processes.

A clinically and serologically distinct overlap entity, MOG antibody–associated disease (MOGAD), is now considered separate from NMOSD but shares phenotypes; ~70–80% of NMOSD is AQP4-IgG+, a minority is MOG-IgG+ (now reclassified), and a small "double-seronegative" group remains.

Epidemiology: female predominance ~9:1 in AQP4+ disease, median onset ~40 years (older than MS), higher prevalence in Black, Asian, and Hispanic populations.

When to suspect NMOSD in a Step 3 stem:

Attacks are more severe and less recovery-prone than MS; permanent disability accrues from attacks rather than insidious progression.

Key distinction: Unlike MS, NMOSD is not a "progressive" disease—disability is relapse-driven, so attack prevention is the entire therapeutic game. MS-disease-modifying therapies (interferon-β, natalizumab, fingolimod) worsen NMOSD—a frequent Step 3 trap.

Board pearl: Any adult with otherwise unexplained intractable hiccups or vomiting >48 hours plus a dorsal medullary MRI lesion should prompt AQP4-IgG testing before steroids cloud the picture.

Presentation Patterns and Key History

— Optic neuritis (ON): subacute monocular or bilateral painful vision loss, central scotoma, dyschromatopsia; often severe (<20/200), bilateral simultaneous ON is far more suggestive of NMOSD than MS.

— Acute myelitis: paraparesis/quadriparesis, sensory level, bowel/bladder dysfunction, paroxysmal tonic spasms, Lhermitte sign, radicular pain. Cervical LETM may cause respiratory failure.

— Area postrema syndrome: intractable hiccups, nausea, vomiting lasting >48 h, often the inaugural attack; commonly misdiagnosed as GI disease.

— Acute brainstem syndrome: diplopia, dysarthria, vertigo, hearing loss.

— Acute diencephalic syndrome: narcolepsy-like hypersomnolence, SIADH, hypothermia.

— Symptomatic cerebral syndrome: encephalopathy with typical NMOSD MRI lesions (more common in pediatrics).

— Tempo: subacute (hours–days), not minutes (rules out stroke) and not chronic progressive (rules out compressive myelopathy).

— Prior unexplained episodes: hiccup attacks, brief vision blurring, transient sensory levels.

— Personal/family autoimmune history: SLE, Sjögren, MG—co-occurrence is common, not a contradiction.

— Vaccination, infection, or pregnancy in preceding weeks (post-partum relapse risk peaks at 3 months).

— Medication exposures: prior diagnosis of "MS" treated with interferon, natalizumab, or fingolimod—worsening on these supports NMOSD reclassification.

Six core clinical syndromes of NMOSD (memorize—2015 IPND criteria use them):

History essentials to elicit:

Step 3 management: When a patient with presumed MS has had atypical severe attacks, bilateral ON, or LETM, stop MS DMT, send AQP4-IgG (cell-based assay) and MOG-IgG before initiating any further immunotherapy.

Board pearl: Paroxysmal tonic spasms—painful, stereotyped, brief tonic posturing of a limb triggered by movement—are highly suggestive of NMOSD myelitis and respond to carbamazepine.

Physical Exam Findings and Functional Assessment

— Decreased visual acuity, often severe (counting fingers or worse) and frequently bilateral.

— Relative afferent pupillary defect (RAPD) in unilateral or asymmetric disease.

— Dyschromatopsia: red desaturation on Ishihara plates is an early, sensitive sign.

— Central or cecocentral scotoma on confrontation; optic disc may be normal acutely (retrobulbar) or swollen; pallor develops weeks later.

— Funduscopy: rule out papilledema (ICP) and retinal pathology.

— Symmetric or asymmetric paraparesis/quadriparesis with upper motor neuron signs (hyperreflexia, Babinski, spasticity)—acutely may show spinal shock with flaccidity and areflexia.

— Well-demarcated sensory level on the trunk; assess pinprick, temperature, vibration, and proprioception separately—NMOSD often produces complete transverse patterns.

— Urinary retention on bladder scan; check post-void residual.

— Lhermitte sign, paroxysmal tonic spasms on provocation.

— Internuclear ophthalmoplegia, intractable hiccups, vertigo, hearing loss, dysphagia.

— Hypersomnolence, hypothermia, syndrome of inappropriate ADH (check Na).

— Bedside FVC and negative inspiratory force (NIF); FVC <15 mL/kg or trending down predicts impending failure.

— Cough strength, paradoxical breathing, accessory muscle use.

Visual exam in optic neuritis:

Spinal cord exam in myelitis:

Brainstem/diencephalic findings:

Respiratory assessment in cervical myelitis:

Functional baseline: document EDSS-relevant items—ambulation distance, transfers, bladder/bowel continence, vision in each eye—because Step 3 vignettes often hinge on disability trajectory to drive therapy intensification.

CCS pearl: In suspected high cervical myelitis, order serial FVC/NIF q4h alongside neuro checks; declining numbers should trigger ICU transfer before overt hypercapnia. Don't wait for ABG to act.

Board pearl: A complete, sharply demarcated sensory level with symmetric paraparesis and urinary retention evolving over hours to days is myelitis until proven otherwise—next step is urgent MRI cord with gadolinium, not lumbar puncture first.

Diagnostic Workup — Initial Imaging, Labs, and Biomarkers

— Spinal cord: longitudinally extensive transverse myelitis (LETM) ≥3 contiguous vertebral segments, central cord predominance on axial views, T2 hyperintensity often with gadolinium enhancement; cervical/upper thoracic predilection.

— Optic nerve: long-segment enhancement (>½ optic nerve length), posterior involvement including chiasm—highly suggestive of NMOSD over MS.

— Brain: usually normal or shows NMOSD-typical lesions—dorsal medulla (area postrema), periependymal around third/fourth ventricles, hypothalamus, corpus callosum (large, edematous), corticospinal tracts. Ovoid periventricular Dawson fingers are MS-like and atypical.

— Serum AQP4-IgG by cell-based assay (CBA)—sensitivity ~75%, specificity >99%. Always send serum, not CSF (higher yield); draw before plasma exchange if feasible.

— MOG-IgG by CBA if AQP4 negative—reclassifies patient as MOGAD with different prognosis/treatment.

— Co-screen for overlapping autoimmunity: ANA, anti-Ro/La, TSH, anti-AChR (especially if bulbar/respiratory symptoms suggest MG overlap).

— Pleocytosis often >50 cells/µL with neutrophils/eosinophils (unusual in MS).

— Elevated protein.

— Oligoclonal bands present in <20% of NMOSD (vs >85% MS)—a key discriminator.

— Send CSF AQP4-IgG only if serum negative and suspicion high.

MRI brain and full spinal cord with and without gadolinium—the single most important initial test.

Serology—the diagnostic anchor:

CSF studies (after MRI, when safe):

Baseline labs before immunotherapy: CBC, CMP, HIV, HBV (HBsAg, anti-HBc, anti-HBs), HCV, QuantiFERON-TB, JCV antibody if rituximab planned, vitamin D, lipid panel, pregnancy test, vaccination status review.

Board pearl: Oligoclonal bands negative + LETM + bilateral severe ON in a middle-aged woman = NMOSD until AQP4-IgG returns.

Step 3 management: Don't delay IV methylprednisolone waiting for AQP4 results—draw serology first, then start steroids the same day for any acute attack.

Diagnostic Workup — Confirmatory Criteria and Advanced Studies

— ≥1 of the 6 core clinical syndromes (optic neuritis, acute myelitis, area postrema syndrome, brainstem syndrome, diencephalic syndrome, cerebral syndrome)

— Positive AQP4-IgG by best available method (CBA preferred)

— Exclusion of alternative diagnoses

— ≥2 core clinical syndromes from separate attacks, with ≥1 being ON, acute myelitis with LETM, or area postrema syndrome

— Dissemination in space (≥2 different core syndromes)

— Additional MRI requirements:

▸ ON: normal brain MRI or NMOSD-typical brain lesions, or optic nerve lesion >½ length or involving chiasm

▸ Acute myelitis: associated LETM ≥3 segments or focal cord atrophy in patients with prior compatible myelitis

▸ Area postrema syndrome: associated dorsal medulla lesion

▸ Brainstem syndrome: associated periependymal brainstem lesion

— OCT (optical coherence tomography): retinal nerve fiber layer thinning quantifies prior ON; severe thinning with single attack favors NMOSD.

— Visual evoked potentials show prolonged P100 latency; useful when ON suspected but vision recovered.

— Urodynamics for chronic neurogenic bladder.

— Repeat AQP4-IgG in 3–6 months if initially negative but clinical suspicion high—seroconversion occurs (especially after plasma exchange clearance).

2015 International Panel for NMO Diagnosis (IPND) criteria—know cold:

NMOSD with AQP4-IgG (seropositive):

NMOSD without AQP4-IgG (seronegative) or unknown status—stricter:

Advanced/adjunctive testing:

Exclude mimics: spinal cord MRI to rule out cord compression, dural AV fistula (look for flow voids), neurosarcoidosis (chest CT, ACE level), SLE/Sjögren myelopathy, B12 deficiency, copper deficiency, HTLV-1, syphilis, paraneoplastic (anti-CRMP5, anti-amphiphysin).

Key distinction: MOGAD vs AQP4-NMOSD—MOGAD favors children, may be monophasic, often involves anterior optic nerve with disc edema, ADEM-like brain lesions, conus involvement, and has better recovery with steroid-responsive course.

Board pearl: A single attack of area postrema syndrome plus a dorsal medullary lesion plus positive AQP4-IgG is sufficient to diagnose NMOSD—no need to wait for dissemination in time.

Acute Attack Management Logic

— Methylprednisolone 1 g IV daily × 5 days, started as soon as attack is recognized, ideally within hours.

— Concurrent PPI, glucose monitoring, BP monitoring, infection screen pre-treatment (chest x-ray, urine, occult infection).

— Follow with oral prednisone taper over weeks–months to bridge to maintenance therapy and prevent rebound (unlike MS, do not stop steroids abruptly in NMOSD).

— Indications: severe attack (e.g., visual acuity <20/200, paraplegia, respiratory compromise), incomplete response to IV steroids within 3–5 days, or as first-line in catastrophic presentations alongside steroids.

— Typical regimen: 5–7 exchanges every other day.

— Earlier PLEX (within days) yields better outcomes; don't wait the full 5-day steroid course in severe cases.

— IVIG 0.4 g/kg/day × 5 days.

— Consider early initiation of preventive therapy (eculizumab, inebilizumab, satralizumab, rituximab) once attack stabilized.

— DVT prophylaxis, bladder management (intermittent catheterization), bowel regimen, pressure-injury prevention, early PT/OT, pain control (gabapentin/pregabalin for neuropathic pain), carbamazepine for tonic spasms.

Treat every NMOSD attack aggressively and early—delay correlates directly with permanent disability because recovery from NMOSD attacks is poor.

Step-1: High-dose IV corticosteroids (first-line for every attack):

Step-2: Plasma exchange (PLEX) — escalate early, do not wait:

Step-3: Add-on options for steroid/PLEX-refractory attacks:

Supportive care during attack:

CCS pearl: Order set on admission—MRI brain + entire spine with contrast, AQP4-IgG, MOG-IgG, CBC, CMP, HIV, HBV/HCV, TB screen, pregnancy test, methylprednisolone 1 g IV daily, PPI, neuro checks q4h, FVC/NIF q4h if cervical cord involved, urology consult for retention, ophtho consult for ON, neurology consult—then re-evaluate at 72 h for PLEX trigger.

Board pearl: In NMOSD, "time is cord and nerve"—each day of delay in PLEX for steroid-refractory attack worsens long-term EDSS.

Pharmacotherapy — Maintenance/Preventive Therapy

— Eculizumab (anti-C5 complement inhibitor): IV q2 weeks. Highest efficacy in trials (PREVENT). Requires meningococcal vaccination ≥2 weeks before initiation (or antibiotic prophylaxis if urgent); risk of meningococcal sepsis. Also vaccinate against H. influenzae, pneumococcus.

— Inebilizumab (anti-CD19 mAb): IV day 1 and 15, then q6 months. Depletes B cells more broadly than rituximab. Monitor IgG levels; hypogammaglobulinemia risk.

— Satralizumab (anti-IL-6 receptor mAb): subcutaneous q4 weeks after loading. Monitor LFTs, lipids, infection risk; masks fever/CRP response—use clinical vigilance for infection.

— Rituximab (anti-CD20): 1 g IV × 2 doses (or 375 mg/m² weekly × 4), redosed q6 months or guided by CD19/CD27 memory B-cell reconstitution. Strong real-world efficacy; cost-effective first-line in many systems.

— Mycophenolate mofetil: 1–1.5 g BID; cheap, oral; slower onset—bridge with prednisone 10–20 mg/day for first 3–6 months.

— Azathioprine: alternative; check TPMT activity before starting to avoid life-threatening myelosuppression.

— Interferon-β, natalizumab, fingolimod, alemtuzumab. These are MS drugs; their use in NMOSD is a classic Step 3 wrong answer.

Goal: zero relapses. Maintenance therapy is lifelong for AQP4-IgG+ NMOSD; start immediately after first attack (do not wait for a second).

FDA-approved agents (AQP4-IgG+ adults):

Off-label/legacy but widely used:

Therapies that WORSEN NMOSD—never use:

Pre-treatment workup: HBV/HCV/HIV/TB screening, vaccinations (live vaccines before immunosuppression), baseline Ig levels, CBC, CMP, meningococcal vaccine for eculizumab.

Key distinction: Eculizumab requires meningococcal vaccination; rituximab/inebilizumab require hepatitis B screening and consideration of antiviral prophylaxis if HBcAb+; azathioprine requires TPMT; mycophenolate is teratogenic—match prerequisite to drug.

Board pearl: A woman with NMOSD asking about pregnancy—avoid mycophenolate and cyclophosphamide; azathioprine and rituximab are relatively preferred (rituximab timed pre-conception with planned pregnancy after B-cell depletion stabilizes).

Expanded Pharmacology and Treatment Selection

— Mechanism: blocks terminal complement, preventing astrocyte lysis from AQP4-IgG.

— Pros: rapid onset, very high relapse-free rates (~98% at 48 weeks in PREVENT).

— Cons: meningococcal infection risk (boxed warning), infusion burden, cost. Vaccinate against serogroups A, C, W, Y AND B ≥2 weeks pre-dose, or give ciprofloxacin prophylaxis if must start sooner.

— Mechanism: depletes plasmablasts and B cells (broader than CD20).

— Pros: q6-month dosing, good efficacy (N-MOmentum trial).

— Cons: progressive hypogammaglobulinemia—monitor IgG, hold for IgG <300 or recurrent infection; infusion reactions.

— Mechanism: blocks IL-6 driven plasmablast survival and Th17.

— Pros: subcutaneous self-administration q4 weeks; mono- or add-on therapy.

— Cons: elevated LFTs, neutropenia, hyperlipidemia; masks acute-phase response—infections may present afebrile with normal CRP.

— Monitor CD19+ B cells or CD27+ memory B cells; redose when memory B cells return rather than fixed q6 months for tighter control.

— Watch for late-onset neutropenia, hypogammaglobulinemia, PML (rare), HBV reactivation.

— Neuropathic pain: gabapentin, pregabalin, duloxetine, amitriptyline.

— Tonic spasms: carbamazepine (classic answer), oxcarbazepine.

— Spasticity: baclofen, tizanidine; intrathecal baclofen for refractory.

— Neurogenic bladder: clean intermittent catheterization, antimuscarinics, mirabegron, β3 agonists; refer urology.

— Fatigue/depression: SSRI, modafinil; treat comorbid sleep apnea.

— Bone health on chronic steroids: calcium, vitamin D, DEXA at baseline and every 1–2 years, bisphosphonate if T-score ≤ −1.5 with steroids ≥3 months.

Choosing between approved monoclonals—Step 3 will rarely test specific selection, but know the trade-offs:

Eculizumab/ravulizumab (anti-C5):

Inebilizumab (anti-CD19):

Satralizumab (anti-IL-6R):

Rituximab (off-label, real-world workhorse):

Symptomatic therapies:

Step 3 management: Patient on rituximab develops recurrent sinopulmonary infections—check IgG levels; if <400 mg/dL with infections, consider IVIG replacement and reassess preventive regimen.

Board pearl: AQP4-IgG seronegative NMOSD has unproven benefit from eculizumab, inebilizumab, and satralizumab in their pivotal trials—rituximab, mycophenolate, or azathioprine are typically chosen.

Special Populations — Elderly, Renal, and Hepatic Impairment

— AQP4-IgG+ disease can present in late life; female predominance persists.

— Higher attack-related disability, slower recovery, more comorbidity (HTN, DM, osteoporosis, infection).

— Steroid-related toxicity magnified: hyperglycemia, delirium, osteoporotic fractures, secondary infection, fluid overload in HF. Use steroid-sparing maintenance promptly and minimize chronic prednisone (<10 mg/day if needed).

— Vaccination status: pneumococcal (PCV20 or PCV15→PPSV23), zoster recombinant, annual influenza, COVID-19—optimize before starting B-cell depletion (live vaccines like zoster live are contraindicated; use recombinant zoster vaccine (Shingrix) which is safe).

— Fall and fracture prevention: home safety eval, PT, DEXA, calcium/vitamin D, bisphosphonate if chronic steroid exposure.

— Methylprednisolone: no major adjustment, but monitor fluid/Na/glucose.

— Mycophenolate: caution if CrCl <25; GI and hematologic toxicity increased.

— Rituximab, eculizumab, inebilizumab, satralizumab: no renal dose adjustment; monoclonals not renally cleared.

— Azathioprine: reduce dose in CKD; monitor CBC closely.

— Cyclophosphamide (rarely used): renally adjust; aggressive hydration, mesna.

— Contrast for MRI: gadolinium—use macrocyclic agents, avoid in eGFR <30 unless essential (nephrogenic systemic fibrosis risk, though lower with newer agents).

— Azathioprine: hepatotoxic—avoid in significant liver disease; if used, monitor LFTs q month initially.

— Satralizumab and tocilizumab-class agents: can elevate ALT/AST—check LFTs q4–8 weeks initially, hold if ALT >5× ULN.

— Mycophenolate: monitor LFTs.

— Screen and treat HBV before any immunosuppression—give entecavir or tenofovir prophylaxis if HBcAb+ to prevent reactivation, especially with rituximab/inebilizumab.

Elderly NMOSD patients (>65 years):

Renal impairment:

Hepatic impairment:

Polypharmacy red flags: azathioprine + allopurinol = catastrophic myelosuppression (reduce azathioprine to 25% or avoid); mycophenolate + antacids reduce absorption.

Board pearl: Before B-cell depletion therapy, always check HBsAg, anti-HBc, anti-HBs—HBcAb+ patients need antiviral prophylaxis throughout treatment and 12 months after.

Step 3 management: Elderly NMOSD patient on chronic prednisone presenting with new back pain—order thoracolumbar spine x-ray for vertebral compression fracture and check 25-OH vitamin D, calcium; this is not a relapse.

Pregnancy and Pediatric Considerations

— Relapse risk is highest in the postpartum period (peak 0–3 months); pregnancy itself may reduce AQP4-attack frequency in some but not reliably—do not stop maintenance therapy.

— Increased risk of miscarriage and preeclampsia in AQP4-IgG+ women.

— Preconception counseling: discuss teratogenicity, drug washout, attack-prevention plan.

— Avoid: mycophenolate (teratogenic—pregnancy category D; 6-week washout required, REMS program), methotrexate, cyclophosphamide, fingolimod.

— Generally acceptable: azathioprine (extensive safety data in IBD/transplant), prednisone (lowest effective dose; minimal placental transfer of methylprednisolone vs dexamethasone).

— Rituximab: ideally given pre-conception; B-cell depletion lasts 6–12 months providing transitional protection. If used late in pregnancy, neonatal B-cell depletion possible—delay live vaccines in infant.

— Eculizumab: limited data but used in PNH pregnancy; reasonable to continue if benefit outweighs risk.

— Acute attack in pregnancy: IV methylprednisolone is safe in all trimesters; PLEX is safe; IVIG safe.

— Vaginal delivery acceptable unless level of cord lesion contraindicates pushing; epidural anesthesia is not contraindicated by NMOSD itself.

— Resume or escalate immunotherapy immediately postpartum to prevent relapse.

— Breastfeeding: prednisone (low dose), azathioprine, and rituximab are generally compatible; mycophenolate is contraindicated.

— Rarer than MOGAD in children; AQP4-IgG+ kids have similar relapsing course as adults and need chronic immunotherapy.

— More common cerebral syndromes (encephalopathy, seizures) and area postrema attacks.

— Treatment: IV methylprednisolone, PLEX, IVIG acutely; rituximab, mycophenolate, azathioprine off-label maintenance. Eculizumab/satralizumab have pediatric data (satralizumab approved ≥12 years).

— Growth, vaccination schedule (complete inactivated vaccines before B-cell depletion), school accommodations, neurocognitive monitoring.

Pregnancy and NMOSD:

Drug safety in pregnancy:

Delivery and postpartum:

Pediatric NMOSD:

Board pearl: A woman on mycophenolate for NMOSD planning pregnancy—switch to azathioprine (after confirming TPMT activity) at least 6 weeks before conception, document on dual contraception in interim.

Step 3 management: Postpartum AQP4+ patient at 2 weeks—even if asymptomatic, resume maintenance immunotherapy now; do not wait for symptoms.

Complications and Adverse Outcomes

— Permanent visual impairment/blindness: severe ON often leaves <20/200; bilateral blindness occurs in ~20% within 5 years untreated.

— Paraplegia/quadriplegia from LETM with poor recovery.

— Neurogenic bladder and bowel: UTI, urosepsis, autonomic dysreflexia in high cord lesions, fecal impaction.

— Neuropathic pain and spasticity: chronic, often disabling.

— Respiratory failure from cervical cord involvement or medullary lesions—leading cause of NMOSD mortality.

— Pressure injuries, DVT/PE, contractures in immobile patients.

— Depression, anxiety, suicide risk—screen with PHQ-9.

— Steroid toxicity: hyperglycemia/steroid-induced DM, osteoporosis, AVN of femoral head (suspect with hip/groin pain on chronic steroids—MRI hip), cataracts, glaucoma, weight gain, mood changes, immunosuppression.

— Eculizumab: meningococcal sepsis (boxed warning), upper respiratory infections.

— Rituximab/inebilizumab: hypogammaglobulinemia, infusion reactions, HBV reactivation, PML (rare), late-onset neutropenia.

— Satralizumab: hepatotoxicity, neutropenia, hyperlipidemia, infections masked.

— Azathioprine: myelosuppression, hepatotoxicity, pancreatitis, increased skin cancer/lymphoma risk—annual dermatology screening.

— Mycophenolate: GI intolerance, leukopenia, infections, teratogenicity.

— Respiratory failure from cervical/medullary attacks, aspiration pneumonia, urosepsis, suicide. Modern treated 5-year mortality has dropped from ~30% in pre-antibody era to <5%.

— Number of attacks in first 2 years, attack severity, age at onset >50, longer interval to treatment initiation, AQP4-IgG+ vs MOGAD (MOGAD generally better recovery).

Disease-related complications:

Treatment-related complications:

Mortality drivers (historical and current):

Long-term disability indicators:

CCS pearl: NMOSD patient on chronic prednisone presents with new groin/hip pain worse with weight-bearing—next step is MRI of the hip (avascular necrosis), not plain x-ray, which is often normal early.

Board pearl: Sudden new fever in an eculizumab-treated patient = meningococcal sepsis until proven otherwise—obtain blood cultures, empiric ceftriaxone immediately, do not wait for LP.

When to Escalate — ICU, Consults, and Triage

— Cervical or high thoracic LETM with declining FVC (<20 mL/kg or trending down by >30%) or NIF (less negative than −30 cmH₂O)—anticipate early intubation before crisis.

— Brainstem/medullary attack with dysphagia, aspiration risk, autonomic instability, refractory hiccups/vomiting causing dehydration and electrolyte derangements.

— Hemodynamic instability from autonomic dysreflexia in high cord lesions (paroxysmal severe HTN, bradycardia) triggered by bladder/bowel distension—identify and remove trigger first, then short-acting antihypertensive (nitroglycerin, captopril).

— Status epilepticus in cerebral syndrome.

— PLEX requiring central venous access in unstable patient.

— Neurology (neuroimmunology if available)—primary management.

— Ophthalmology for ON—document acuity, visual field, OCT.

— Urology for retention and long-term bladder management.

— Physical medicine & rehabilitation—early involvement improves outcomes.

— Apheresis/transfusion medicine for PLEX.

— Infectious disease if pre-treatment screening identifies latent TB, HBV, HIV.

— Psychiatry if mood disorder or steroid-induced psychosis.

— Maternal-fetal medicine if pregnant.

— Inpatient: any acute attack warrants admission for IV methylprednisolone, monitoring, and rapid PLEX availability.

— Outpatient: stable patients on maintenance therapy with routine infusions, symptomatic management, and surveillance.

— Discharging after attack without confirmed maintenance therapy plan and follow-up appointment within 2–4 weeks.

— Failure to communicate "avoid MS DMTs" to receiving providers.

— Vaccination gaps before next infusion cycle.

— Bridging steroid taper schedule unclear—handoff orders should specify exact taper.

ICU admission criteria:

Mandatory consults at presentation:

Inpatient vs outpatient triage:

Transitions of care landmines (Step 3 favorite):

CCS pearl: When advancing the clock on inpatient NMOSD myelitis: q4h neuro checks + q4h FVC/NIF + daily CBC/CMP/glucose + bladder scans + DVT prophylaxis + early PT/OT consult on day 1, schedule PLEX on day 3 if not improving, consult ophtho/urology same day, document maintenance plan before discharge.

Board pearl: Any NMOSD patient with FVC <15 mL/kg, NIF > −20 cmH₂O, or rising PaCO₂—intubate electively; emergent intubation in established hypercapnia has worse outcomes.

Key Differentials — Inflammatory Demyelinating Mimics

— MS lesions: small (<2 vertebral segments), peripheral/dorsolateral cord, ovoid periventricular brain lesions ("Dawson fingers"), juxtacortical, infratentorial.

— OCBs positive in >85% of MS, negative in most NMOSD.

— MS attacks recover more completely; NMOSD attacks leave more deficit.

— AQP4-IgG negative in MS.

— Now a distinct entity, not part of NMOSD.

— Often monophasic (40–50%), more anterior optic nerve involvement with disc edema, ADEM-like brain lesions in children, conus medullaris involvement, leptomeningeal enhancement.

— Better steroid response and recovery.

— Test MOG-IgG by CBA in serum; low-titer results need cautious interpretation.

— Typically post-infectious or post-vaccinal in children; encephalopathy is required; multifocal brain and cord lesions; usually monophasic.

— May be MOG-IgG+.

— LETM possible; leptomeningeal and dural enhancement, basal predominance, cranial neuropathy, hilar adenopathy on chest CT, elevated ACE (insensitive), CSF lymphocytic with low glucose, biopsy showing non-caseating granulomas.

— Treat with steroids + steroid-sparing (MTX, TNF-α inhibitors).

— Coexist with NMOSD often; LETM can occur in primary connective tissue disease. Check ANA, anti-dsDNA, anti-Ro/La. If AQP4-IgG+, the diagnosis is NMOSD with concurrent autoimmunity.

Multiple sclerosis (MS): the single most important differential.

MOG antibody–associated disease (MOGAD):

Acute disseminated encephalomyelitis (ADEM):

CNS sarcoidosis:

CNS lupus and Sjögren myelopathy:

Behçet's disease: brainstem predilection, oral/genital ulcers, uveitis, pathergy.

Chronic relapsing inflammatory optic neuropathy (CRION): steroid-dependent recurrent ON; many are now reclassified as MOGAD.

Key distinction: OCB-positive, small dorsolateral cord lesions, Dawson fingers, AQP4-IgG negative → MS. OCB-negative, LETM, central cord, AQP4-IgG positive → NMOSD. Bilateral ON with disc edema, conus involvement, MOG-IgG+ → MOGAD.

Board pearl: A patient previously diagnosed with "MS" who worsened on interferon-β or natalizumab—reconsider NMOSD and test AQP4-IgG and MOG-IgG immediately.

Key Differentials — Non-Demyelinating Mimics

— Spondylotic cervical myelopathy, disc herniation, epidural abscess, epidural metastasis, hematoma.

— First MRI in any acute myelopathy rules these out before assuming inflammatory cause.

— Red flags: fever and back pain (epidural abscess), anticoagulation (hematoma), known cancer (metastasis).

— Hyperacute onset (minutes to hours), anterior spinal artery territory, post-aortic surgery, atherosclerosis, fibrocartilaginous embolism.

— MRI shows "owl-eye" or pencil-like anterior cord T2 hyperintensity, DWI restriction; spares posterior columns.

— Older men, progressive myelopathy with stepwise worsening, lower thoracic cord T2 hyperintensity with flow voids on MRI; angiography confirms.

— Viral: HSV, VZV, enterovirus, West Nile, HIV, HTLV-1 (tropical spastic paraparesis), CMV.

— Bacterial: TB (Pott disease, arachnoiditis), syphilis (tabes dorsalis).

— Parasitic: schistosomiasis (eosinophilic, travel history).

— Screen with HIV, RPR, HTLV-1, VZV PCR in CSF, travel-specific testing.

— B12 deficiency (subacute combined degeneration): dorsal columns + lateral corticospinal tracts; macrocytic anemia, low B12, elevated MMA/homocysteine.

— Copper deficiency: similar to B12, history of bariatric surgery, zinc excess.

— Nitrous oxide abuse ("whippets")—functionally inactivates B12.

— Ischemic optic neuropathy (NAION—older, painless, altitudinal field defect, disc edema with hemorrhages; AAION—GCA, ESR/CRP elevated, jaw claudication).

— Leber hereditary optic neuropathy (young men, painless sequential bilateral).

— Toxic/nutritional (methanol, ethambutol, B12).

Compressive myelopathy:

Spinal cord infarction:

Dural arteriovenous fistula:

Infectious myelitis:

Metabolic/nutritional:

Vascular/autoimmune systemic: vasculitis (PAN, GPA), antiphospholipid syndrome with cord involvement.

Neoplastic: astrocytoma, ependymoma, lymphoma, paraneoplastic myelopathy (anti-CRMP5, anti-amphiphysin, anti-GFAP astrocytopathy).

Optic neuritis mimics (when ON is the presentation):

Board pearl: Painless, altitudinal visual field defect in a 65-year-old with vasculopathic risk factors and a swollen disc = NAION, not ON—do not give steroids, evaluate for GCA with ESR, CRP, and temporal artery biopsy.

Step 3 management: In any acute myelopathy, MRI with contrast is the first imaging study—not LP, not CT—to exclude compression before any LP or immunotherapy.

Secondary Prevention and Long-Term Plan

— Start immediately after first attack; do not wait for second event.

— Continue indefinitely; discontinuation is associated with severe relapse, even after years of stability.

— Switch agent if breakthrough attack on adequate therapy, intolerance, or serious adverse event.

— Before immunosuppression (especially B-cell depletion): inactivated influenza annually, pneumococcal (PCV20 or PCV15→PPSV23), recombinant zoster (Shingrix), HPV if age-appropriate, Tdap, COVID-19 boosters, hepatitis B if non-immune, meningococcal ACWY + B if eculizumab planned.

— Avoid live vaccines on immunosuppression (MMR, varicella, yellow fever, live attenuated influenza, oral typhoid). Time live vaccines ≥4 weeks before immunosuppression.

— Calcium 1000–1200 mg/day, vitamin D 800–2000 IU/day.

— DEXA at baseline and every 1–2 years on chronic steroids; bisphosphonate if prednisone ≥7.5 mg/day for ≥3 months or T-score ≤ −1.5.

— Monitor BP, fasting glucose/A1c, lipids—steroids and IL-6 inhibitors raise risk.

— Lifestyle counseling: smoking cessation (smoking accelerates NMOSD disability), Mediterranean diet, exercise within tolerance.

— Screen for depression (PHQ-9) and anxiety (GAD-7) at each visit; treat aggressively—suicide risk is elevated.

— Neuropsychologic testing if cognitive complaints.

— Scheduled intermittent catheterization, bowel regimen, urology q6–12 months, urodynamics as needed.

— Document visual acuity—advise patient and report per state law if vision falls below driving threshold (typically 20/40 corrected).

Lifelong maintenance immunotherapy in AQP4-IgG+ NMOSD:

Vaccination strategy:

Bone health:

Cardiovascular and metabolic:

Cancer screening on schedule: colon, breast, cervical, lung (if eligible), skin (annual dermatology especially on azathioprine).

Mood and cognition:

Bladder/bowel program:

Driving and visual function:

Step 3 management: At each follow-up: review attack count, EDSS, infusion timing, vaccination status, bone health, mood, vision, bladder, contraception/pregnancy plans, and confirm no MS drugs prescribed by other providers.

Board pearl: The single most important secondary prevention intervention in NMOSD is uninterrupted immunotherapy—missed doses correlate with breakthrough attacks within weeks.

Follow-Up, Monitoring, and Rehabilitation

— Neurology every 3 months in year 1, then every 6 months if stable.

— Sooner for new symptoms—any new neurologic symptom lasting >24 hours is a potential attack; same-day evaluation, low threshold for MRI and admission.

— Rituximab/inebilizumab: CBC, CMP, IgG, CD19/CD27 B-cell counts every 3 months; redose by clinical schedule or B-cell return. HBV viral load q3 months if HBcAb+ on prophylaxis.

— Satralizumab: LFTs, lipids, CBC every 4–8 weeks initially then quarterly.

— Eculizumab: routine CBC; vigilance for infection; meningococcal vaccine boosters per CDC.

— Azathioprine: CBC and LFTs every 2 weeks × 1 month, then monthly × 3, then every 3 months.

— Mycophenolate: CBC, CMP monthly × 3, then quarterly; pregnancy test in women of childbearing potential.

— MRI brain and spine annually or with new symptoms; not for routine surveillance the way MS is monitored (NMOSD attacks are clinical, not radiologic).

— Visual acuity, color vision, fields, and OCT annually to quantify subclinical RNFL thinning.

— Early PT/OT during admission and continued outpatient; gait training, transfer training, adaptive equipment.

— Speech therapy for dysphagia/dysarthria; videofluoroscopic swallow study if aspiration concern.

— Vocational rehab for return-to-work planning; reasonable workplace accommodations (ADA).

— Driving evaluation if visual or motor impairment.

— Recognize attack symptoms (new vision loss, weakness, sensory level, intractable vomiting) and seek care within 24 hours.

— Medication adherence; never stop maintenance therapy abruptly.

— Pregnancy planning—discuss before conception.

— Infection precautions on immunosuppression—fever workup with low threshold.

— Medical alert bracelet noting NMOSD and current immunosuppressant.

Outpatient follow-up cadence:

Laboratory monitoring by therapy:

Imaging surveillance:

Ophthalmology:

Rehabilitation:

Patient counseling key points:

CCS pearl: Schedule the next infusion and the next clinic visit before discharge, and document them on the after-visit summary—Step 3 rewards explicit, timed follow-up.

Board pearl: Subclinical OCT thinning between attacks can occur in NMOSD—annual OCT is a sensitive way to detect smoldering optic pathway injury and may prompt treatment escalation.

Ethical, Legal, and Patient Safety Considerations

— Eculizumab consent must include meningococcal sepsis risk, REMS program enrollment, and need for ongoing vaccination/prophylaxis.

— Rituximab/inebilizumab: discuss PML (rare), HBV reactivation, hypogammaglobulinemia, infusion reactions, fetal B-cell depletion if pregnancy possible.

— Document discussion of alternatives, including off-label rituximab vs FDA-approved agents, with shared decision-making about cost, dosing burden, and side-effect profile.

— Severely visually impaired patients still retain decision-making capacity; provide large-print, Braille, or audio consent materials and verbal review. Avoid surrogate consent unless capacity is otherwise impaired.

— Many states require physician reporting of patients with visual acuity below driving thresholds or seizure activity. Counsel and document the conversation; report per state statute.

— Never write "MS" on the discharge summary for an NMOSD patient—downstream prescribers may start interferon or natalizumab, which worsens NMOSD. Use precise diagnostic language and a prominent allergy/precaution flag.

— Reconcile medications carefully; ensure steroid taper, next infusion date, and PCP follow-up within 2 weeks are explicit.

— Use closed-loop communication when handing off to outpatient neurology; confirm receipt of records.

— Live vaccine in a pediatric patient on immunosuppression—weigh risk; coordinate with ID and pediatrics; defer when possible.

— Mycophenolate REMS requires two forms of contraception and pregnancy tests; document counseling. Respect patient's reproductive decisions while clearly communicating teratogenic risks.

— Advance directives discussion in patients with high-cervical recurrent attacks or respiratory involvement; ventilator preferences, code status, palliative care referral when appropriate.

— Document functional limitations for FMLA, short/long-term disability, ADA workplace accommodations, and school IEPs in pediatric cases.

— NMOSD disproportionately affects Black, Asian, and Hispanic patients—be alert to diagnostic delays, access barriers to expensive biologics, and insurance prior-authorization hurdles; engage social work and patient assistance programs early.

Informed consent for high-risk therapies:

Capacity and visual impairment:

Mandatory reporting and driving:

Transition-of-care safety (Step 3 hot zone):

Vaccination ethics:

Pregnancy and reproductive autonomy:

End-of-life and severe disability:

Disability accommodations:

Health equity:

Board pearl: A misdiagnosis of MS in an NMOSD patient leading to interferon-β use and accelerated disability is a classic preventable adverse event—the safety net is AQP4-IgG testing in any atypical demyelinating presentation.

High-Yield Associations and Rapid-Fire Facts

Antibody target: AQP4 water channel on astrocyte foot processes; complement-mediated astrocyte injury → secondary demyelination.

Demographics: female:male 9:1 (AQP4+); median age 40; overrepresentation in Black, Asian, Hispanic populations.

Six core syndromes: optic neuritis, acute myelitis, area postrema syndrome, brainstem syndrome, diencephalic syndrome, cerebral syndrome.

LETM: ≥3 contiguous vertebral segments, central cord predominance—the signature spinal MRI finding.

Area postrema: intractable hiccups/nausea/vomiting + dorsal medullary lesion = NMOSD until proven otherwise.

OCBs: present <20% NMOSD vs >85% MS—a fast discriminator.

CSF pleocytosis: often >50 cells with neutrophils—unusual for MS.

Bilateral simultaneous severe ON: think NMOSD, not MS.

Paroxysmal tonic spasms: respond to carbamazepine.

MS drugs worsen NMOSD: interferon-β, natalizumab, fingolimod, alemtuzumab.

Acute attack: IV methylprednisolone 1 g × 5 days; PLEX early if severe or refractory.

FDA-approved maintenance (AQP4+ adults): eculizumab, inebilizumab, satralizumab; ravulizumab as longer-acting C5 inhibitor.

Off-label workhorses: rituximab, mycophenolate, azathioprine.

Eculizumab: meningococcal vaccine ≥2 weeks before dose (serogroups ACWY + B); boxed warning for meningococcal sepsis.

Azathioprine: check TPMT activity; avoid with allopurinol (catastrophic myelosuppression).

Mycophenolate: teratogenic—6-week washout before conception; REMS program.

Rituximab: monitor CD19/CD27 B cells, IgG; HBV screen and prophylaxis if HBcAb+.

Pregnancy: highest relapse risk postpartum 0–3 months; resume immunotherapy immediately.

MOGAD: distinct entity; anterior ON with disc edema, monophasic possible, better recovery, may not need lifelong therapy.

Coexisting autoimmunity: SLE, Sjögren, myasthenia gravis, autoimmune thyroid—test broadly.

Mortality driver: respiratory failure from cervical/medullary attacks.

Tonic spasms drug: carbamazepine. Neuropathic pain: gabapentinoids. Spasticity: baclofen.

OCT: RNFL thinning quantifies ON damage; useful for surveillance.

Board pearl: AQP4-IgG by serum cell-based assay is the highest-yield single test in suspected NMOSD; draw before plasma exchange for maximal sensitivity.

Board Question Stem Patterns

— Young-to-middle-aged Black or Asian woman with prior episodes of optic neuritis and now LETM; MRI brain "non-specific"; CSF OCB negative.

— Trap answer: start interferon-β. Correct: send AQP4-IgG, start IV methylprednisolone, plan PLEX if severe.

— Patient hospitalized for 2 weeks of vomiting/hiccups, GI workup negative; subtle neuro signs emerge.

— Correct: MRI brain looking for dorsal medullary lesion, AQP4-IgG.

— Bilateral simultaneous painful vision loss to count-fingers in a 35-year-old.

— Correct: IV methylprednisolone, AQP4/MOG-IgG; do not assume MS.

— No improvement after 3–5 days of methylprednisolone.

— Correct: initiate plasma exchange (5–7 sessions every other day).

— Known NMOSD on interferon-β with new attacks.

— Correct: stop interferon, switch to rituximab or FDA-approved monoclonal.

— Patient on eculizumab presents with fever and headache.

— Correct: blood cultures, empiric ceftriaxone immediately, evaluate for meningococcal sepsis; confirm meningococcal vaccination status.

— NMOSD woman on mycophenolate wants to conceive.

— Correct: switch to azathioprine (after TPMT testing) ≥6 weeks pre-conception, contraception bridge, consult MFM.

— 6 weeks postpartum with new visual loss.

— Correct: IV methylprednisolone, MRI, restart/escalate immunotherapy; consider PLEX if severe.

— Painful brief stereotyped limb posturing in NMOSD patient.

— Correct: carbamazepine.

— Patient's FVC drops from 30 to 15 mL/kg over 6 hours.

— Correct: ICU transfer, elective intubation, expedite PLEX.

— Profound pancytopenia 2 weeks after azathioprine started.

— Correct: stop drug, supportive care; TPMT deficiency or allopurinol interaction missed.

— Recurrent ON with disc edema, good recovery, MOG-IgG+.

— Correct: diagnose MOGAD, not NMOSD; treatment overlaps but prognosis differs.

Pattern 1 — The atypical MS:

Pattern 2 — Intractable hiccups misdiagnosed as GI:

Pattern 3 — Severe bilateral ON:

Pattern 4 — Steroid-refractory attack:

Pattern 5 — Therapy gone wrong:

Pattern 6 — Eculizumab and fever:

Pattern 7 — Pregnancy planning:

Pattern 8 — Postpartum relapse:

Pattern 9 — Tonic spasms:

Pattern 10 — Cervical myelitis with declining FVC:

Pattern 11 — TPMT and azathioprine:

Pattern 12 — AQP4 negative, MOG positive:

Step 3 management: When stem says "previously diagnosed with MS but progressed on interferon," next test is AQP4-IgG; next therapeutic step is stop interferon, treat current attack, and start NMOSD-appropriate maintenance.

One-Line Recap

— Diagnose: severe ON, LETM ≥3 segments, or area postrema syndrome → send AQP4-IgG (serum, CBA) and MOG-IgG; MRI brain + entire spine with contrast; CSF if compression excluded—OCBs usually negative.

— Treat the attack hard and fast: IV methylprednisolone 1 g daily × 5 days within hours of recognition; escalate to plasma exchange (5–7 sessions every other day) by day 3–5 if no improvement or for severe attacks (vision <20/200, paraplegia, respiratory compromise); bridge with oral prednisone taper.

— Prevent relapses for life: start maintenance after the first attack; choose eculizumab/ravulizumab (meningococcal vaccination required), inebilizumab, satralizumab, or rituximab; avoid interferon-β, natalizumab, fingolimod, alemtuzumab; mycophenolate/azathioprine as cost-effective alternatives with appropriate pre-screening (TPMT, HBV).

— Manage the long tail: postpartum relapse prophylaxis, pregnancy-compatible regimens (azathioprine, low-dose prednisone, rituximab pre-conception), vaccination before immunosuppression, bone/vision/bladder surveillance, OCT annually, mood screening, and explicit transition-of-care documentation that prevents downstream "MS" misdiagnosis and inappropriate interferon prescribing.

Neuromyelitis optica spectrum disorder is a relapsing AQP4-IgG astrocytopathy whose disability is attack-driven, whose attacks demand immediate IV methylprednisolone and early plasma exchange, and whose prevention requires lifelong immunotherapy with eculizumab, inebilizumab, satralizumab, or rituximab—never MS disease-modifying drugs.

Recap bullets — the four things to never miss:

Board pearl: If you remember only one thing for Step 3—AQP4-IgG testing changes the entire treatment paradigm, and MS drugs harm NMOSD patients; recognizing this distinction is the single highest-yield decision in the topic.