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 2 · Diagnosis

The differential

How Lambert-Eaton, botulism, ALS, eye-muscle disease, brainstem lesions, Miller Fisher, congenital and drug-induced myasthenia are told apart from MG. Press play to sweep the features column by column, ending with the nerve test that separates MG from Lambert-Eaton; pick a condition to compare it with MG.

MG weakens muscles that are moved on purpose and spares the pupils, the reflexes and sensation. A finding outside that pattern points away from MG: a dilated pupil, absent reflexes, a dry mouth, numbness, weakness since birth, or a muscle response that jumps after 10 seconds of effort. ^{179,227,276,367,404,516}

Compare MG with

Timeline

like MGpoints away from MGoverlaps or sometimes— not described in the sources used here

Schematic, not to scale. Matrix cells summarise the cited text shown in the box under the note and in the profile below. The traces are drawn shapes: thresholds (10% decrement, 60% and 100% increment) and the LEMS increment after 5–10 s of exercise (filled dot, about 244%) are published values; other heights are illustrative (open dots).

Which answer points away from MG?

Each finding below is something a person might report or a clinician might find. Click one to see whether it fits MG or points elsewhere. Findings that point away light up the matching rows in the matrix above; click again to clear.

Exam hookLambert-Eaton: proximal leg weakness, dry mouth and areflexia; a low first CMAP that rises 60% or more (classically 100%) after 10 s of exercise or 50 Hz stimulation; P/Q-type VGCC antibodies in 91–100%; small-cell lung cancer in about half. MG: normal first CMAP, low-rate decrement of 10% or more, normal reflexes and pupils. ^{1,227,276,290,316,367,404,405,517}

In plain wordsSeveral other conditions also cause drooping lids or tiring muscles. MG leaves the pupils, the reflexes and feeling alone, and comes and goes over the day. Reflexes, pupils, how the illness started, and a nerve test that compares the muscle's response before and after a short effort help tell them apart.

Lambert-Eaton: the tumour score

The DELTA-P score (Dutch-English LEMS Tumour Association Prediction) gives one point for each item present at or within 3 months of onset. It was built to predict small-cell lung cancer in people with LEMS. It is a published research score, shown here to illustrate the study's numbers; it is not a diagnosis. ⁵¹⁸

Look-alikes in brief

Lambert-Eaton (LEMS)

A presynaptic disease: antibodies against P/Q-type voltage-gated calcium channels cut acetylcholine release. Found in 100% of 32 LEMS with cancer and 91% of 33 without; N-type antibodies in 49%. Low titres also appear in 23% of sporadic ALS and 24% of people with cancer but no neurological disease. ³¹⁶

About half have small-cell lung cancer. After exercise, the increment was largest with 5–10 s of effort (about 243–244%) and smallest with 30 s (84%). ^227,517

Botulism

Cranial nerve palsies, then a symmetric descending flaccid paralysis in an alert, afebrile person. Ptosis 81%, diplopia 75%, dysphagia 85%, dilated pupils 37%. 87% of those intubated were intubated on hospital day 1 or 2. Asymmetry (6–15%) does not exclude it. ^74,442

Thyroid eye disease, alone or with MG

Proptosis, pain and restricted, often asymmetric eye movements with enlarged muscles on imaging. The two can coexist: 0.23% of 6,576 TED patients also had MG, where ptosis and exotropia were the clues. When both are present, one positive test may not be enough. ^2,81,287

Drug- and checkpoint-inhibitor MG

D-penicillamine induces true AChR-antibody MG in up to 7%, mostly mild and ocular. Checkpoint inhibitors cause MG in about 0.5%, mostly with PD-1/PD-L1 blockade, a median 4 weeks after the first dose, often with myositis or myocarditis; mortality 20–30%. ^302,471 Drugs that can worsen MG

Mimics that were treated as MG

In one series, 8 of 61 patients had been wrongly treated as refractory MG for a mean of 9 years; 2 had a thymectomy. Of 80 people first labelled double-seronegative MG, 36% had another diagnosis, most often a functional disorder (45%), then OPMD. ^225,331

Magnesium: a chemical look-alike

A high blood magnesium produces a LEMS-like presynaptic picture that tends to spare the eye muscles. ³⁰²

Congenital myasthenic syndromes: one drug, opposite effects

Congenital myasthenic syndromes (CMS) are inherited, not autoimmune: 32 genes are known (8 presynaptic, 4 synaptic, 15 postsynaptic, 5 glycosylation). Most respond to acetylcholinesterase inhibitors, 3,4-DAP, salbutamol, ephedrine or fluoxetine, but which drug helps depends on the gene. ¹⁷⁹

Drug class	May help	May worsen or fail
Acetylcholinesterase inhibitors	Many CMS forms	May worsen COLQ, LAMB2, DOK7, MUSK and LRP4 CMS ¹⁷⁹
Fluoxetine	Slow-channel CMS	Worsened MYO9A and RAPSN CMS ¹⁷⁹
3,4-diaminopyridine (3,4-DAP)	Many CMS forms	May be ineffective in CHRNE or MUSK CMS ¹⁷⁹

A drug that helps one form can harm another, which is why the gene matters before treatment in CMS. ¹²⁶ Drug choices are made by the treating clinician.

Every condition in one table

Click a row to load it into the comparison above.

Condition	Typical pattern	What points away from MG	Key test