Myasthenia gravis: an animated, cited guide

This page needs JavaScript for its animations. The outline and key answers are below, and every claim in the full version carries a numbered citation.

Not medical advice. Myasthenia Gravis Companion is an educational synthesis of published literature. It does not replace a clinician.

What is in it

What myasthenia gravis is Who gets it, the numbers, the muscles it reaches.
The neuromuscular junction One nerve impulse in slow motion, and the safety factor.
Antibodies at the junction AChR, complement, MuSK and LRP4, animated.
Weakness over a day Why muscles tire with use and recover with rest.
Diagnosis Antibodies, nerve tests, single-fibre EMG, a calculator.
MGFA class & scores MGFA classes I to V, MG-ADL and QMG, scored live.
The differential Lambert-Eaton, botulism, ALS, eye and muscle disease.
Pyridostigmine, animated Buying time at the receptor, dose by dose.
The treatment ladder From symptom relief to immunotherapy and biologics.
Thymectomy over the years The thymus, thymoma and the MGTX trial.
Complement & FcRn inhibitors The newer biologics, trial week by trial week.
Myasthenic crisis Triggers, the breathing numbers, ICU care.
Drugs that can worsen MG A cited checker: antibiotics, magnesium and more.
Nursing care Assessment, timing the doses, teaching, documentation.
Living with MG Pregnancy, surgery, exercise, vaccines, work.
Toward a cure CAR-T, B-cell targets and the evidence for each route.
History & people From Willis in 1672 to the biologics.
Flashcards, quiz and glossary Revision for students.
Sources Every reference behind the guide.

Part 4 · Crisis, care & the future

Myasthenic crisis

Myasthenic crisis is MG weakness severe enough to need help with breathing. Press play to follow a schematic 21-day course: the trigger, falling breathing numbers, BiPAP or intubation, plasma exchange or IVIG, and weaning. Then compare myasthenic and cholinergic crisis.

Trouble breathing or swallowing is an emergency. In a person with MG, new or worsening trouble breathing, swallowing or speaking can be the start of a crisis. Nursing teaching material tells patients to contact their prescriber urgently for trouble swallowing, speaking or breathing, and the MGFA emergency alert card warns first responders that breathing or swallowing difficulty may signal a crisis and can be mistaken for intoxication. ^353,410 This module describes published studies and guidance. It is not medical advice and cannot tell anyone what to do in an emergency.

What counts as crisis. The international consensus defines manifest crisis as worsening severe enough to need intubation, or noninvasive ventilation to avoid intubation (MGFA class V, unless the intubation is routine after surgery). Impending crisis is rapid worsening that, in the treating physician's opinion, could lead to crisis within days to weeks. Crisis can come from weak breathing muscles or from bulbar weakness with collapse of the upper airway. ^82,271,476

Who and when. About 15-20% of people with MG have at least one crisis; other reviews give 10-20%, or one-fifth to one-third of generalized MG. It usually happens in the first 2-3 years: median 8 months from first symptoms in one series. In about one-fifth, crisis is the first sign of MG. ^{75,82,254,512,547}

1 · Three weeks of a crisis, schematic

Trigger

Course

Rescue

Days 0-21

vital capacity / MIPMEPMG study thresholdsreview thresholdsdashed: 20/30/40 rule (GBS)

Schematic: one illustrative course, not a real patient. The lines are modelled, not measured; their anchors are published: the thresholds, the onset times of plasma exchange (about 2 days) and IVIG (about 4-5 days), BiPAP results, and the share of people extubated by day 7, 13 and 31. The breath count is derived from the rule of thumb "count × 100 ≈ FVC in mL" for a 70 kg adult. Day 0 is the first worsening; intubation is placed on day 4.5. ^{113,486,511,512,547}

2 · The breathing numbers

Measure	MG studies and reviews	The "20/30/40" rule (Guillain-Barré, Lawn 2001)
Vital capacity	Ventilation unlikely above 20 mL/kg (42 people with severe MG). A review: under 1 L, or under 20-25 mL/kg, signals significant weakness. Lower VC before and at admission went with worse outcomes. ^383,511,547	Under 20 mL/kg ³⁰⁸
Maximal inspiratory pressure (MIP, NIF)	Ventilation unlikely when more negative than −40 cmH2O; a fall of 30% or more marked higher risk. A review: weaker than −20 cmH2O signals significant weakness. ^511,547	Weaker than 30 cmH2O ³⁰⁸
Maximal expiratory pressure (MEP)	Ventilation unlikely above 40 cmH2O; a review says below 40 may signal crisis. ^511,547	Under 40 cmH2O ³⁰⁸
Fall over time	A small ICU series found repeated VC, even with 20 or 13 mL/kg cut-offs, did not separate episodes that needed ventilation, which the authors put down to MG's erratic course. ⁴⁵²	A fall of more than 30% in any of the three ³⁰⁸
Single breath count	Count aloud on one deep breath at 2 counts per second, seated: ≥25 fits normal breathing muscles; difficulty reaching 20 signals expiratory weakness. It correlated with FVC, NIF and neck flexor strength in 31 people with AChR MG. The MG Core Exam scores it 0 (≥30), 1 (25-29), 2 (20-24) or 3 (<20). ^{103,113,214,547}	Not part of the rule
Blood gases and oximetry	PaCO2 above 45 mmHg at BiPAP start was the only predictor of BiPAP failure (above 50 in an earlier series). Oxygen saturation can look normal while CO2 is high: 54% of one neuromuscular group with high CO2 had SpO2 ≥95%, in chronic (not acute) respiratory failure. ^208,437,486	Not part of the rule

The 20/30/40 cut-offs come from 114 people with severe Guillain-Barré syndrome. A neuromuscular review notes the rule was proposed for that disease, and no MG-specific validation of the full rule was found in the sources read. No single tool predicts neuromuscular respiratory failure well; a combined, repeated bedside assessment is preferred. ^308,342,534

3 · Plasma exchange or IVIG: where the sources disagree

Consensus Expert opinion

The 2016 international consensus: trials suggest the two work equally well in impending or manifest crisis, but "expert consensus suggests that PLEX is more effective and works more quickly". A 2023 review says plasmapheresis "is preferred", and a crisis-centre guideline favours PLEX. ^82,270,476

Randomized trials RCTs

87 people in exacerbation: muscle score change at day 15 +18 with 3 PLEX vs +15.5 with IVIG; side effects in 8 vs 1. ¹⁸⁴
84 with moderate-to-severe worsening: IVIG 1 g/kg/day × 2 as effective as 5 PLEX at day 14 (69% vs 65% improved). ³⁴
Meta-analysis: QMG difference −2.8 favouring PLEX, not significant, with a trend to faster effect in the first 2 weeks. ⁴¹⁹

Crisis cohorts Observational

54 crises: PLEX gave better breathing at 2 weeks and function at 1 month, with more complications (13 vs 5). ⁴³⁶
US inpatient data: similar outcomes, possible cost advantage for IVIG. ³³³
Germany: PLEX or immunoadsorption first went with less invasive ventilation, and IVIG first with more weaning failure (OR 2.53); another German cohort found no difference. ^383,384,385

Who gets which

The consensus ties the choice to the person: PLEX is avoided in sepsis, IVIG in hypercoagulable states, renal failure or immunoglobulin hypersensitivity. Regimens in one review: IVIG 400 mg/kg/day for 5 days, or 5 plasma exchanges over 10 days. Any regimen for a person is set by the treating clinician. ^476,547

4 · Myasthenic or cholinergic crisis?

Cholinergic crisis is rare now. The consensus says cholinergic crises are now rare, though too much cholinesterase inhibitor cannot always be ruled out as a cause of worsening; one crisis series found no cholinergic cases at all. The pyridostigmine label says the two crises may be difficult to distinguish on symptoms, and that cholinergic crisis calls for prompt withdrawal of these drugs. ^151,476,547

The old edrophonium test. The edrophonium (Enlon) label lists use for evaluating emergency treatment in myasthenic crises, with atropine 1 mg ready and a warning to watch a patient in crisis for bradycardia or cardiac standstill. The consensus documents read do not recommend the test in crisis; no guideline sentence saying "avoid" was found. ^138,476

Tap the signs below. Each one drops into the column the sources point it to. The tilt only counts the taps: it is a study aid, not a way to tell the two crises apart.

Points to myasthenic (too little effect)

Points to cholinergic (too much drug)

Seen in both

Not in the sources read

Sources for each sign appear in the columns. Muscarinic signs (sweating, tearing, salivation, nausea, diarrhoea, slow heart) and fasciculations come from a crisis review and the edrophonium label. ^138,547

5 · How long it lasts, and who stays longer

Group figures from one series of 73 crises (1983-1994), not a prediction for one person. Relative hazards: bicarbonate 4.5, VC 2.9, age 2.4. ⁵¹²

Time on the ventilator

12 daysmedian in 250 ventilated German crises; 20.5% of survivors still needed ventilation at discharge. Mean 10.4 days at Mayo; median hospital stay 17 days for intubated patients in a review. ^384,486,547

Tracheostomy

49.8%of ventilated crises had one. Ventilation lasted 34.4 days with tracheostomy vs 7.9 without, and early tracheostomy (by day 10) was linked to about 2 weeks less ventilation and ICU stay. ¹⁸

MuSK antibodies

43 vs 17 daysventilation in MuSK-only vs AChR crises (43.0 vs 17.4); ICU stay 45.3 vs 21.2 days. Severity at diagnosis, thymoma and MuSK antibodies independently predicted crisis or exacerbation in 815 patients; thymoma-associated MG reached crisis sooner. ^253,299,383

Newer drugs in crisis Early evidence

C5 inhibitors in 17 crises not responding to standard therapy: 82% left ICU/IMC within 6 weeks; 2 died of sepsis; no meningococcal infection. ¹⁹³
Emergency eculizumab, 5 episodes: QMG 28.2 to 15.0 within 48 h. ²⁵⁵
Efgartigimod, 16 with impending crisis, no control arm: 75% met the MG-ADL endpoint at week 8; in 10 crises all were weaned. ^492,501

Case series and single-arm studies only; no randomized trial in crisis was found. ^193,492

6 · Deaths per crisis, then and now

All bars are published values. The cohorts differ: the German one was ventilated only and older (median age 72), which its authors called comparable to earlier reports given age and disease burden; in the Chinese cohort, all-cause mortality over about 29 months was 15.16%, mostly septic shock and multiorgan failure. A review gives 5-12%. At Columbia all deaths came from overwhelming medical illness. ^{16,84,254,384,512,534}

Exam hookCrisis = needs intubation or NIV (MGFA V). Lifetime risk 15-20%, mostly in the first 2-3 years; commonest trigger infection. Follow the trend of VC, MIP and the breath count: SpO2 can stay normal while CO2 climbs. MG thresholds: VC 20 mL/kg, MIP −40, MEP 40; 20/30/40 is a Guillain-Barré rule. PLEX acts in ~2 days, IVIG in ~4-5.

In plain wordsA crisis means the muscles for breathing or swallowing have become too weak to do the job safely, so a machine has to help for a while. It is an emergency. An infection is the most common spark, but often no cause is found. With intensive care, most people today survive and come off the ventilator, though some need weeks.