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Myasthenia gravis
1. DR. DHILEEBAN MAHARAJAN P
SENIOR RESIDENT
DEPARTMENT OF NEUROLOGY
NEIGRIHMS
Myasthenia Gravis
2. Introduction
Autoimmune disorder of NMJ
AChR antibody mediated destruction of AChR
Impaired transmission of nerve impulse across NMJ
Lead to muscle weakness
Effective treatments are available
3. Epidemiology
MG begin at any age
Incidence - 0.3 to 2.8 per 100,000
Worldwide Prevalence- >700,000
Women : Men – 3:1 (<40 years)
After 50 years M > F
4. Clinical Presentation
Ptosis or diplopia - Initial symptom (2/3)
Difficulty chewing, swallowing, or talking (1/6)
Limb weakness (10%)
Fluctuating Weakness
Maximum weakness within one year in 2/3 of patients
Remission, Relapse, Active stage, Burn-out stage
weakness or dysfunction that typically worsens with activity
and improves with rest
10. 80%–85% Generalised MG patients have anti-AChR antibodies
Complement-mediated destruction of the folds
Accelerated internalization
Degradation of AChR
T lymphocytes play a pivotal role
10% - Antibodies to muscle specific tyrosine kinase (MuSK)
predominantly IgG4
Double seronegative - Agrin, LRP4
Immunopathology
11. Thymus in Myasthenia Gravis
Abnormal in most MG patients
70% - Lymphoid follicular hyperplasia
10% - Thymoma
Thymic-derived AChR subunits may serve as an antigen for the
auto-sensitization against the AChR
13. Ocular MG (OMG)
10%–15% of all MG
Weakness remains limited to the ocular muscles after 2 years
Ptosis and/or diplopia - Initial symptoms of MG (85%)
Both symptoms within 2 years of disease onset
More common in Asian populations
RNS studies and anti-AChR antibodies are often negative
Single-fiber EMG (SFEMG) testing may be required.
15. Early onset MG
Generalized MG < 40 years
Common in females
AChR AB + and High
Thymus hyperplasia +
65% of all MG
HLA -DR3 B8 DR9
• GMG > 40 years
• Common in males
• AChR ab usually lower
• Thymus normal or atrophied
• ≈ 50% have Titin and RyR AB
• HLA-A3, B7, DR2, HLA-DR4
Late onset MG
16. Thymomatous Myasthenia Gravis
In 10%–15% of MG patients
Thymic epithelial tumor or thymoma
M = F
Occur at any age (peak onset at 50)
17. MuSK-Antibody Myasthenia Gravis
MuSK ab - 50% in GMG with AchR ab –
Mostly affects females
Begin from childhood through middle age
Predominant weakness in cranial and bulbar muscles
Marked atrophy of muscles
Prominent neck, shoulder, and respiratory weakness, with little or
no involvement of ocular or bulbar muscles
18. Electrodiagnostic abnormalities are not conclusive
Do not improve with ChEIs (some actually become worse)
Improve dramatically with therapeutic plasma exchange (PLEX)
or corticosteroids
Long-term outcome is generally good
Thymic changes are absent or minimal
Thymectomy in MuSK-MG is not yet clear
MuSK-Antibody Myasthenia Gravis
20. Seronegative Myasthenia Gravis
Lack both anti-AChR and anti-MuSK antibodies
No evidence of thymoma
Low affinity anti-AChR antibodies can be detected using
specialized assays
Less severe MG than seropositive MG patients
23. Diagnostic Procedures
Diagnostic
testing
Repetitive nerve
stimulation
Anti cholinesterase
test
Assay for acetyl
cholinesterase
Receptor antibody
Single fiber
electromyography
EDROPHONIUM
Unequivocal
improvement in
objectively weak
muscle is
positive
Decrementel
response of 15%
Is considered
positive
Human AchR
labeled with alpha
bungarotoxin
Delayed or failed
NMT in pairs of
muscle fibres
supplied by br of
24. Edrophonium Chloride Test
Facilitates repeated interaction of ACh with the reduced AChRs
Only unequivocal improvement in strength of an affected muscle
Also seen in
congenital myasthenic syndromes (CMS)
Lambert–Eaton syndrome (LES)
intracranial aneurysms
brainstem lesions
cavernous sinus tumors
Maximum - 10 mg IV (2mg, 3mg, 5mg)
Neostigmine methylsulfate, 0.5 mg IM or SC
26. Acetylcholine Receptor Antibodies
AChR-ab binding assay
Specific serologic markers for MG
Sensitivity - 85% for GMG
Normal antibody measurements do not exclude
Auto-Antibodies
27. Anti-striational Muscle Antibodies
First autoantibodies discovered in MG.
Muscle cytoplasmic proteins (titin, myosin, actin, and ryanodine receptors)
60% of patients with MG with onset before age 50, who have elevated StrAbs
have thymoma
Anti-MuSK Antibodies
Antibodies to MuSK are present in up to 50% of GMG patients who are
seronegative for AChR abs and in some patients with OMG
Auto-Antibodies
28. Electrodiagnostic Testing
Repetitive nerve stimulation (RNS) – Commonly used
Decrementing response of at least 10% to trains of 2–3 Hz
stimulation
Sensitivity - 53% to 100% in GMG and 10% to 48% in OMG
SFEMG
Most sensitive
Shows increased jitter
30. Ocular Cooling (Ice pack Test)
Myasthenic weakness typically improves with muscle cooling
Cooling of a ptotic lid improves lid elevation
Useful in patients with lid ptosis, particularly if the edrophonium
test is negative or contraindicated
35. 1. Symptomatic and immunosuppressive (IS) treatments
2. IV immunoglobulin (IVIg) and plasma exchange (PLEX)
3. Impending and manifest myasthenic crisis
4. Thymectomy
5. Juvenile MG (JMG)
6. MG with antibodies to muscle-specific tyrosine kinase
(MuSK-MG)
7. MG in pregnancy
Guidance statements were developed for :
36. Preliminary definitions
Minimal Manifestation Status (MMS)
The patient has no symptoms or functional limitations from MG
but has some weakness on examination of some muscles
Remission
The patient has no symptoms or signs of MG. Weakness of eyelid
closure is accepted, but there is no weakness of any other muscle
on careful examination
37. Ocular MG
Any ocular muscle weakness. May have weakness of eye closure.
Strength in all other facial, bulbar, and limb muscles is normal.
Impending myasthenic crisis
Rapid clinical worsening of MG that, in the opinion of the treating
physician, could lead to crisis in the short term (days to weeks)
Preliminary definitions
38. Manifest myasthenic crisis
Worsening of myasthenic weakness requiring intubation or non-
invasive ventilation to avoid intubation, except when these
measures are employed during routine postoperative management
Refractory MG
PIS is unchanged or worse after corticosteroids and at least 2 other
IS agents, used in adequate doses for an adequate duration, with
persistent symptoms or side effects that limit functioning, as
defined by patient and physician
Preliminary definitions
39. Symptomatic And Immunosuppressive (IS)
Treatment Of Mg
Pyridostigmine - Initial treatment in most cases
Dose adjusted based on symptoms
Ability to discontinue pyridostigmine - Patient met treatment goals
Corticosteroids or IS therapy - not met Rx goals after an adequate trial
A non-steroidal IS agent should be used alone when corticosteroids are
contraindicated or refused
A non-steroidal IS agent used initially with corticosteroids when the risk of
steroid side effects is high
40. A non-steroidal IS agent should be added to corticosteroids when:
Significant side effects
Inadequate response to an adequate trial of corticosteroids
Corticosteroid dose cannot be reduced d/t symptom relapse
Following IS agents may also be used in refractory MG
Chronic IVIg and chronic PLEX
Cyclophosphamide
Rituximab
Symptomatic And Immunosuppressive (IS)
Treatment Of Mg
41. IS Agent Dosage And
Duration Of Treatment
Once patients achieve treatment goals, the corticosteroid dose
should be gradually tapered
In many patients, continuing a low dose of corticosteroids long-
term can help to maintain the treatment goal
For non-steroidal IS agents, once treatment goals have been
achieved and maintained for 6 months to 2 years, the IS dose
should be tapered slowly to the minimal effective amount
42. Dosage adjustments should be made no more frequently than every
3–6 months
Tapering of IS drugs is associated with risk of relapse
Risk of relapse is higher in symptomatic, or after rapid taper
Usually maintenance immunosuppression is needed for many years
Monitored for potential adverse effects and complications from IS
drugs
Changing to an alternative IS agent should be considered if adverse
effects and complications occurs
IS Agent Dosage And
Duration Of Treatment
43. INDICATIONS FOR IVIG AND PLEX
Short-term treatment in patients with MG with life-threatening
signs such as respiratory insufficiency or dysphagia
In preparation for surgery in patients with significant bulbar
dysfunction
When a rapid response to treatment is needed
When other treatments are insufficiently effective
Prior to beginning corticosteroids if deemed necessary to prevent
or minimize exacerbations
44. Depends on individual patient factors and the availability
Equally effective in the treatment of severe GMG
Efficacy of IVIg is less certain in milder MG or in ocular MG.
PLEX may be more effective than IVIg in MuSK-MG
The use of IVIg as maintenance therapy can be considered for
patients with refractory MG or for those in whom IS agents are
relatively contraindicated
INDICATIONS FOR IVIG AND PLEX
45. Impending and Manifest
Myasthenic Crisis
Emergent situations - Aggressive management and supportive
care.
Although cholinergic crises are rare, excessive ChEI cannot be
completely excluded as a cause of clinical worsening.
ChEIs increase airway secretions, which may exacerbate
breathing difficulties.
46.
47. Myasthenic Crisis
PLEX and IVIg are the mainstay of management
Impending crisis requires hospital admission and close
observation of respiratory and bulbar function, with the ability to
transfer to an ICU if it progresses to manifest crisis
PLEX and IVIg are used as short-term treatment for impending
and manifest myasthenic crisis and in patients with significant
respiratory or bulbar dysfunction
48. Corticosteroids or other IS agents are often started at the same
time to achieve a sustained clinical response.
Clinical trials - IVIg= PLEX
Expert consensus - PLEX> IVIg
A greater risk of hemodynamic and venous access complications
with PLEX may be minimized by using peripheral rather than
central venous access.
Myasthenic Crisis
49. Thymectomy in MG
Non-thymomatous MG - Thymectomy is an option to
potentially avoid or minimize the dose or duration of
immunotherapy
Thymectomy for MG is an elective procedure
Should be performed when the patient is stable
Value of thymectomy in the treatment of pre-pubertal patients
with MG is unclear.
50. Considered in children with generalized AChR ab positive MG-
If the response to pyridostigmine and IS therapy is unsatisfactory
In order to avoid potential complications of IS therapy
For Seronegative generalized MG, the possibility of a
congenital myasthenic syndrome or other neuromuscular
condition should be entertained
Current evidence does not support an indication for
thymectomy in patients with MuSK, LRP4, or agrin antibodies
Thymectomy in MG
51. All patients with MG with thymoma should undergo surgery
to remove the tumor
All thymus tissue should be removed along with the tumor
Further treatment of thymoma will be dictated by histologic
classification and degree of surgical excision
Incompletely resected thymoma - Surgery with an interdisciplinary
treatment approach (radiotherapy, chemotherapy)
Thymectomy in MG
52. Juvenile MG
Children with ocular MG are more to go into spontaneous remission
Initial therapy - pyridostigmine.
Immunotherapy - if goals of therapy are not met
Children are at particular risk of steroid side effects-
Eg. - Growth failure, poor bone mineralization, and susceptibility to
infection
Corticosteroids should use the lowest effective dose to minimize side effects
Maintenance PLEX or IVIg are alternatives to IS drugs
53. MG WITH MuSK ANTIBODIES
Respond poorly to ChEIs
Respond well to corticosteroids and steroid-sparing IS agents
Dependent on prednisone despite concomitant treatment with steroid-
sparing agents
MuSK-MG responds well to PLEX, while IVIg seems to be less effective
Rituximab should be considered as an early therapeutic option in
patients with MuSK-MG who have an unsatisfactory response to initial
immunotherapy
54. MG IN PREGNANCY
Planning for pregnancy should be instituted well in advance
Majority of women can be reassured that they will remain stable throughout
pregnancy.
If worsening occurs, it may be more likely during the first few months after
delivery
Oral pyridostigmine is the first-line treatment
IV ChEIs may produce uterine contractions
Thymectomy should be postponed until after pregnancy, as benefit is unlikely to
occur during pregnancy
Prednisone is the IS agent of choice during pregnancy
55. Azathioprine and cyclosporine are relatively safe
Mycophenolate mofetil and methotrexate - teratogenic
PLEX or IVIg are useful during pregnancy.
Spontaneous vaginal delivery should be the objective
Magnesium sulfate is not recommended
Barbiturates or phenytoin usually provide adequate treatment
All babies born to myasthenic mothers should be examined for
evidence of transient myasthenic weakness
MG IN PREGNANCY
57. Differential diagnosis
CONDITIONS
SYMPTOMS AND
CHARECTERISTICS
COMMENT
Congenital myasthenia
syndromes
Rare, early onset non
autoimmune disorder
Specialized EP &
immunocytochemical test
Drug induced Myasthenia
Penicillamine,procainamide,
aminoglycosides
Triggers autoimmune
Myasthenia
Recovery within weeks of drug
withdrawal
Lambert Eaton syndrome
Weakness, fatigue, areflexia
60% A/W oat cell
carcinoma
Incremental response to RNS,
Abs to calcium channel present
Hyperthyroidism Exacerbation of Myasthenia Thyroid function abnormal
Graves disease Diplopia,opthalmoplegia Thyroid stimulating Ig present
Botulism
Generalized weakness,
opthalmoplegia
Incremental response , pupils
are dilated
Intracranial mass
compressing CN
Opthalmoplegia , CN
palsies
Abnormalities on CT or MRI
58. Disorders Associated with Myasthenia
Associated disorders
Recommended lab
test and procedure
Disorder of Thymus Thymoma , hyperplasia MRI or CT of Mediastinum
Autoimmune Disorders
Thyroiditis, Graves disease,
Rheumatoid arthritis, SLE, skin
disorders and F/H/O autoimmune
disorders
Test for Rh-factor, Thyroid function
test, ANA
Disorders That May
Exacerbate Myasthenia
Hypo or hyperthyroidism, Occult
infection and Drugs
Disorders That May Interfere
With Therapy
Tuberculosis, diabetes, peptic ulcer,
renal disease, hypertension ,asthma,
Osteoporosis
Tuberculin test, Chest X-Ray, FBG,
Pulmonary function test, Bone
densitometry
59. Drugs that may Exacerbate MG
Drugs with important
interactions in MG
Antibiotics
Amino glycosides eg. SM, Tobra, Kana
Quinolones eg. Cipro, Levo, O, Gati
Macrolides eg. Erythro, azithro
Cyclosporine
Broad Range of drug interactions which may
raise or lower cyclosporine levels
Non Depolarizing Muscle Relaxants
Curare, Pancuronium, Ve, Atracurium
Azathioprine
Avoid Allopurinol- combination leads to
myelosuppression
Beta Blockers
Propranolol, Atenolol, Metoprolol
LA and related agents
Procaine, Xylocaine (Large amts)
Procainamide (anti arrhythmic)
Botulinum Toxin
Quinine derivatives
Quinine, quinidine, Chloro, Meflo
Magnesium (Decrease Ach Release)
60. Myasthenic Crisis
Respiratory failure from myasthenic weakness
Precipitating Factors – Infection, Surgery, Aspiration, Medication
Cholinergic crisis is respiratory failure from overdose of ChEIs
Admit the patient to an Intensive Care Unit
Serial measurements of Negative Inspiratory Force (NIF)
NIF less than –20 cm H2O
When tidal volume less than 4 to 5 cc/kg body weight and maximum
breathing capacity less than three times the tidal volume
Forced vital capacity less than 15 cc/kg body weight.
61. Many case series report short-term benefit from PLEX and IVIg in
myasthenic crisis
Retrospective studies suggest that both are equally effective in
disease stabilization
Once ventilated, discontinuing ChEIs is safe and recommended
Extubation
when the patient has a NIF greater than –20 cm H2O and an
expiratory pressure greater than 35 to 40 cm H2O
Myasthenic Crisis
64. LAMBERT–EATON SYNDROME (LES)
Immune-mediated attack against the P/Q type voltage-gated calcium channels (VGCC)
Neuromuscular junction and Autonomic ganglia
Gradual onset lower extremity weakness, autonomic dysfunction
Usually after 40 years
60% patients have an underlying malignancy (80% - small-cell lung cancer)
Tendon reflexes absent
Compound muscle action potentials (CMAPs) with low amplitude, which increases
during 20 to 50 Hz stimulation and after brief maximum voluntary muscle activation