Myasthenia gravis: A quick guide to management 1
MYASTHENIA GRAVIS: A QUICK GUIDE TO MANAGEMENT
Professor Yasser Metwally… www.yassermetwally.com
5 - 7% familial
Age of onset
May start at any age.
Rare before 15 or after 70.
60 per cent has onset between the ages of 20 and 40
Due to the increased proportion of older persons, more older patients are found to have MG
Early onset: onset before 50 yo
Late onset: onset after 50 yo
likely to be more severe
myopathy is more common
Effect of acetylcholinesterase inhibitors is often temporary.
Plasma exchange has more complications in the elderly
Result of thymectomy is poorer
Classification after Ossreman & Genkins
Group I: Ocular (20%)
Group IIA: Mild generalized (30%)
Group III: Acute fulminating (11%), rapid onset, early respiratory involvement, high mortality.
Group IV: Late Severe (9%), > 2 years after onset.
Transient Neonatal MG: 1/6 born to MG mother. Last a few weeks.
Congenital Myasthenic Syndrome:
Anti-acetylcholine receptor Ab:
Present in 80% of patient
Ocular 55% positive
Mild Generalized 80% positive
Myasthenia gravis: A quick guide to management 2
Moderately severe or acute 100% positive
Chronic severe 89%
In remission 24%
Antibodies to striated muscle (StrAb)
Positive in 30% of all adult onset MG.
Highly associated with thymoma
Positive in 80% of MG patients with thymoma
Positive in 24% of patients with thymoma without MG.
Seronegativity does not exclude thymoma.
Most useful as a marker of thymoma in patients with MG onset before age 40.
A progressive rise in StrAbs titer after resection of thymoma is a good indicator of tumor recurrence.
A valuable marker in middle-aged or elderly patients with mild MG, where they can be the only
serologic abnormality. False positives are rare in patients without MG and/or thymoma.
Sometimes positive in patients with rheumatoid arthritis who are treated with penicillamine, in 3-5% of
patients with Lambert-Eaton myasthenic syndrome, and in recipients of bone marrow allografts with
graft vs. host disease.
15% of patient has thymoma, 50% has thymic hyperplasia.
Antiskeletal muscle Ab are detected in 90% of patients with thymoma.
CT Chest detect over 85% of thymoma.
Removal of thymoma produces a delayed improvement of MG 6 - 24 months later. Sustained
improvement in > 50%, probably less in older patients. No known long-term side effects.
Tensilon test (Edrophonium)
Given in incremental doses. Start with 2 mg, observe the response for 45 to 60 seconds, followed by
doses of 3 and 5 mg and observation for a clinical response for 1 to 2 minutes following each dose.
During the injection, patients often experience 1 to 3 minutes of increased salivation, mild sweating,
perioral fasciculations and mild nausea.
Hypotension and bradycardia are extremely rare but precautions should be taken. Atropine sulfate (0.6
mg intramuscular or intravenously) should be available in case of an emergency.
Positive means unequivocally improvement of weakness.
Slight to moderate improvement in muscle strength must be interpreted with extreme caution.
Mild to moderate clinical improvement after tensilon has been reported in: brain stem lesions,
oculomotor palsy due to cerebral artey aneurysm, diabetic abducens paresis and even in normal control
Electrophysiology: Repetitive stimulation at 3 hertz.
>10% decrement of compound action potential.
Single fiber EMG: Increased jitter: jitter is the varying time interval between the triggered muscle action
potential in 2 muscle fibers within the same motor unit. Positive in over 90%.
Myasthenia gravis: A quick guide to management 3
Principles of treatment
Onset before age 60
Thymectomy, pretreat with plasmapheresis, cholinesterase inhibitors
If response unsatisfactory before or after thymectomy, consider high dose daily prednisone and/or other
Onset after age 60
Cholinesterase inhibitors with prednisone, azathioprine or other immunosuppressant
Plasmapheresis for severe exacerbations
Anticholinesterase useful in all forms
For patient with thymoma, thymectomy is indicated in all ages. They may spread in the mediastinum.
Plasmapharesis is effective, but practical only on a short term basis.
Tab: 60 mg, half life 4 hrs, take 1 q 4 while awake
Time Span: 180 mg, irregular absorption, use at night only.
IV: 2 mg = 60 mg of oral dose
Side effect: diarrhea, treat with Lomotil or Imodium
Insufficient control w Mestinon
Diplopia rarely respond to Mestinon alone
Start at 100 mg to avoid treatment failure. After remission obtained, switch to alternate day dose, slow
taper over 6 to 12 months. Patient may get weaker initially.
Exacerbation is common.
Initial dose 2-3 mg/kg/day.
Mertens: Complete remission 40%, partial remission 51%, minimal improvement 6.4%, no effect in
Improvement begins in 2-3 months, peaks in 6-15 months.
Keep WBC above 3000/ml.
Monitor liver function weekly X 3 months, then 2x/month.
Sometimes used in combination with steroid.
If above treatment fails, consider Cyclosporine (Sandimmune)
Myasthenia gravis: A quick guide to management 4
5 mg/kg/day, in bid dose. Monitor BP, renal function, Cyclosporine level, Amylase, Cholesterol.
May cause nephropathy, hypertension, hirsutism, liver function abnormality, opportunistic infection,
may increase risk of malignancy.
Plasma Exchange: short term improvement
Human Immune Globulin: Probably effective
Drugs that may adversely affect MG
Aminoglycosides: Neomycin, Gentamycin
Peptide: Polymyxin B, Colistin
Other: tetracycline, Clindamycin, Erythromycin, Ampicillin
Neuromuscular blockers: Botulinum Toxin
Cardiac drugs: Quinine, Quinidine, Procanamide, Lidocaine, Beta blockers, Calcium Channel Blockers
Miscellaneous: Dilantin, Oxytocin, Lithium, Magnesium, Diazapam, D penicillamine, Cloroquine,
Corticosteroids may initially produce worsening of MG.
Other causes of exacerbation
Major Physical Stress
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