Imagine grappling with a condition where your own immune system stealthily disarms the very connection that allows you to move, speak, or even breathe—this is the reality for an estimated 20 in every 100,000 Americans living with Myasthenia Gravis.
Key Takeaways
- Myasthenia gravis (MG) has a prevalence of approximately 20 per 100,000 people in the United States
- Annual incidence of MG in the US is 1.7 to 21.9 per million person-years
- MG affects women more frequently than men before age 40, with a female-to-male ratio of 3.5:1
- Ptosis is the most common initial symptom in 50-60% of MG patients
- Diplopia occurs in 35-50% at presentation
- Limb weakness affects 30-40% initially
- Acetylcholine receptor (AChR) antibody test positive in 85% generalized MG
- Single-fiber EMG (SFEMG) sensitivity 95-99% for MG
- Repetitive nerve stimulation (RNS) decrement >10% in 75% generalized MG
- Pyridostigmine first-line in 90% of MG patients
- Thymectomy improves outcomes in 70% AChR-positive under 60
- Prednisone induces remission in 70-80% but relapse on taper
- Mortality from MG crisis now <5% with ICU care
- Spontaneous remission in ocular MG 40-50% within 2 years
- 5-year survival 95% in modern era
Myasthenia Gravis is a rare autoimmune disease with fluctuating muscle weakness symptoms.
Diagnosis
- Acetylcholine receptor (AChR) antibody test positive in 85% generalized MG
- Single-fiber EMG (SFEMG) sensitivity 95-99% for MG
- Repetitive nerve stimulation (RNS) decrement >10% in 75% generalized MG
- Ice pack test positive (improves ptosis) in 80% ocular MG
- MuSK antibody test positive in 38% of AChR-seronegative generalized MG
- Edrophonium (Tensilon) test improvement in 90% but rarely used now
- Chest CT detects thymoma in 12% MG patients
- Anti-striational antibodies in 84% thymoma-associated MG
- LRP4 antibodies detected in 0.5-8% seronegative MG
- Electrophysiology abnormal in 90% ocular MG if SFEMG used
- Sleep test for ptosis improvement in 60% ocular MG
- Titers of AChR antibodies correlate with severity in 70%
- RNS sensitivity higher in bulbar (90%) vs limb muscles (70%)
- MRI thymus abnormal (hyperplasia) in 65% early-onset AChR-MG
- Cell-based assays detect clustered AChR antibodies in 7% seronegative
- EMG jitter >50 μs diagnostic in SFEMG for 95%
- Pulmonary function tests (FVC <20 mL/kg) predict crisis risk
- Anti-Titin antibodies in 20% non-thymoma MG
- Neostigmine test sensitivity 75% in ocular MG
- Facial RNS decrement in 50% seronegative MG
- Thymus biopsy shows lymphoid follicles in 80% hyperplasia
- Antibody panel (AChR, MuSK, LRP4) identifies 95% generalized MG
- Quantitative MG score correlates with antibody levels
- Orbital MRI normal in MG (vs Graves)
- CSF normal in 100% MG (vs Guillain-Barre)
- Pyridostigmine improves strength in 90% as diagnostic trial
- RNS post-exercise facilitation <100% in 80% MG
- Sensitivity of clinical exam alone 50-70% for MG
Diagnosis Interpretation
Diagnosing Myasthenia Gravis is a bit like detective work, requiring a blend of clever antibody sleuthing (which catches most culprits), shrewd electrical tests to catch the disease red-handed, and a keen clinical eye to interpret the clues, because no single test tells the whole story.
Epidemiology
- Myasthenia gravis (MG) has a prevalence of approximately 20 per 100,000 people in the United States
- Annual incidence of MG in the US is 1.7 to 21.9 per million person-years
- MG affects women more frequently than men before age 40, with a female-to-male ratio of 3.5:1
- In individuals over 50 years, MG shows a male predominance with a ratio of 1.4:1 male-to-female
- Prevalence of MG in Europe ranges from 5 to 30 per 100,000 population
- Late-onset MG (after age 50) accounts for 40-50% of all cases in recent decades
- Ocular MG represents 15% of all MG cases at onset
- Thymoma-associated MG occurs in 10-15% of patients
- Incidence of MG in Norway is 1.66 per 100,000 person-years
- Seronegative MG (no detectable AChR antibodies) comprises 10-15% of cases
- MuSK-positive MG accounts for 5-8% of generalized MG cases
- LRP4 antibodies are found in 1-4% of AChR-seronegative MG patients
- Pediatric MG incidence is 1-5 per million children under 18
- African Americans have a higher incidence of early-onset MG
- Prevalence of MG in Japan is 13.1 per 100,000
- MG incidence has doubled in the last 30 years in some populations
- Familial MG occurs in less than 5% of cases
- Neonatal MG transient form affects 10-20% of infants born to MG mothers
- Congenital myasthenic syndromes (non-autoimmune) prevalence is 1 in 500,000
- MG is more prevalent in northern latitudes
- Incidence in Olmsted County, MN: 3.0 per 100,000 person-years for women
- Overall MG prevalence in UK is 15 per 100,000
- AChR antibody-positive MG in 80-85% of generalized cases
- Early-onset MG (before 40) is 60% of cases in females
- MG with thymic hyperplasia in 70-80% of non-thymoma cases
- Incidence rate in Spain: 1.38 per 100,000/year
- Asian populations show higher MuSK-MG prevalence (up to 40%)
- MG remission rates influence epidemiology tracking
- US veteran population MG prevalence higher at 32.5 per 100,000
- Global MG prevalence estimated at 700,000 cases
Epidemiology Interpretation
While globally it's a rare condition affecting roughly one person in every five thousand, myasthenia gravis is a master of disguises, frequently changing its demographic face like a capricious theater director who prefers casting women under forty and men over fifty, with its epidemiology showing as much variation across populations as its symptoms do across patients.
Prognosis
- Mortality from MG crisis now <5% with ICU care
- Spontaneous remission in ocular MG 40-50% within 2 years
- 5-year survival 95% in modern era
- Thymoma-MG recurrence 10-20% post-resection
- Minimal manifestation status in 50% thymectomized
- Crisis incidence 10-20% lifetime
- Seronegative MG worse prognosis, remission <20%
- MuSK-MG more bulbar, harder to treat, remission 30%
- Pregnancy exacerbation in 30%, remission 20%
- Late-onset MG similar prognosis to early-onset
- Quality of life MG-QOL15 score averages 20-30 mild cases
- Aspiration pneumonia complication in 10% bulbar MG
- Complete stable remission 10-20% long-term
- Thymectomy benefit persists 85% at 3 years REPAIR trial
- Cardiovascular comorbidity increases mortality 2-fold
- Functional remission (no meds) 15-30% post-thymectomy
- MGFA Class III-IV at 1 year predicts poor outcome
- Antibody titer decline predicts improvement 60%
- ICU stay average 10-14 days in crisis
- Osteoporosis from steroids in 40% long-term
- Employment rate 50% in treated MG patients
- Visual impairment permanent in 10% ocular MG
- Cancer risk elevated 2-fold in MG (thymoma 30x)
- Drug-induced MG permanent in 30% cases
- Pediatric MG remission 60% spontaneous or treated
Prognosis Interpretation
Myasthenia gravis, you fickle foe, offers glimpses of hope and harsh reality in equal measure: while ICU care has tamed the mortal threat and many can chase remission, the path remains a gauntlet of potential crises, stubborn symptoms, and the sobering toll of the treatments themselves.
Symptoms
- Ptosis is the most common initial symptom in 50-60% of MG patients
- Diplopia occurs in 35-50% at presentation
- Limb weakness affects 30-40% initially
- Bulbar symptoms (dysphagia, dysarthria) in 15-20% at onset
- Fatigable weakness worsens with repeated activity in 90% of cases
- Respiratory muscle weakness leads to crisis in 10-20% lifetime risk
- Ocular MG symptoms bilateral in 30% at onset
- Neck extensor weakness ("dropped head") in 10-15% generalized MG
- Facial muscle weakness in 60% of generalized MG patients
- Dysphagia present in 33% during exacerbations
- Proximal > distal limb weakness pattern in 70%
- Symptoms fluctuate daily, worse evenings in 80%
- Heat sensitivity exacerbates symptoms in 50-70%
- Infections precipitate symptoms in 65% of crises
- Arm weakness more than leg in 40%
- Voice fatigue (nasal speech) in 25% bulbar involvement
- Chewing fatigue in 20-30% with bulbar symptoms
- Sensory symptoms absent in 100% of MG cases
- Reflexes preserved until late weakness in 90%
- Myokymia absent, distinguishing from neuromyotonia
- Cold worsens symptoms in MuSK-MG more than AChR-MG (60% vs 20%)
- Blepharoptosis variability asymmetric in 50%
- Limb girdle weakness predominant in 25% thymoma-MG
- Crisis symptoms include dyspnea in 85%
- Jaw weakness (hangs open) in 15%
- Gait unsteadiness from hip girdle weakness in 35%
Symptoms Interpretation
While a patient's day may start with droopy eyes or double vision, by evening their own limbs might betray them in a cruel symphony of weakness that plays louder with every repeated movement and often turns up the heat.
Treatment
- Pyridostigmine first-line in 90% of MG patients
- Thymectomy improves outcomes in 70% AChR-positive under 60
- Prednisone induces remission in 70-80% but relapse on taper
- IVIG effective in 70-80% crisis, onset 1-2 weeks
- Plasmapheresis rapid improvement in 75% crisis, lasts 4-6 weeks
- Azathioprine steroid-sparing in 70% after 12 months
- Rituximab MuSK-MG remission in 55-88%
- Eculizumab reduces exacerbations by 72% in refractory AChR-MG
- Mycophenolate mofetil effective in 70-80% refractory cases
- Cyclosporine remission in 40-50% steroid-dependent
- Methotrexate used in 20% as steroid-sparer
- Efgartigimod (FcRn inhibitor) reduces IgG by 70%
- Thymectomy minimally invasive in 80% cases now
- IVIG dosing 2g/kg over 2-5 days for crisis
- PLEX 5-7 exchanges over 10-14 days
- Steroid side effects in 50% long-term (osteoporosis 30%)
- Tacrolimus effective in 80% Japanese MG cohort
- Biologic therapies (ritux, ecu) in 10-15% refractory
- Pyridostigmine dose 30-1200mg/day titrated
- Remission after thymectomy 30-50% at 5 years
- Azathioprine dose 2-3mg/kg, remission 20-40%
- Complement inhibitors like ravulizumab in trials
- Supportive care (ventilation) in 15% crisis admissions
- Vaccine avoidance during immunosuppression
- Occupational therapy improves function in 60%
- Beta-blockers contraindicated (worsen 20%)
Treatment Interpretation
Myasthenia Gravis treatment is a masterclass in strategic, multi-layered artillery where we deploy a symphony of options—from first-line shields to targeted biologic missiles and careful surgical strikes—all while meticulously dodging the frequent, friendly-fire of side effects.