Myasthenia gravis

A 35 years old woman comes to the clinic complaining of double vision that seems to worsen near he end of the day.She also complains of difficulty in chewing meat and other hard foods.She notices that her symptoms improve following a good night’s sleep.on neurologic examination, you note a snarling appearance when the patient is asked to smile, & a nasal tone is heard in her voice.You also note the weakness in the upper extremities when the patient is asked to clench her fist around your finger repeatedly.

“It is an acquired autoimmune

neuromuscular junction disorder

characterized clinically by weakness of

skeletal muscle and rapid fatigability on

exertion”

1) Estimated annual incidence is 2 per

1,000,000 in US( from research)

2) Mortality rate: previously it was 40 to 50

% now it is 2 to 3 %

3) Sex: female:male ratio is 6:4

4) Age: presents at any age. Mean age of

onset is 28 years in females and 42 years

in males.

1)Thyroid diseases

2)SLE

3)Rheumatoid arthritis

4)Pernicious anemia

5)Various drugs can exacerbate symptoms

of myasthenia gravis which are

lithium,procainamide,verapamil,quinidin

e,propranolol,aminoglycosides,erythrom

ycin,timolol etc.

A)Type 2 hypersensitivity reaction

Antibodies target the Ach receptor

results in receptor blockage,down

regulation of receptor and compliment

mediated destruction thus reducing

the number of receptors available to

interact with the ACh released from the

presynaptic nerve terminal

B)Compliment activation attracts

activated macrophages which cause

significant damage to the syneptic

fold,loss of voltage gated sodium

channels muscle weakness and

fatigability.

According to the Myasthenia Gravis

Foundation of America (MGFA) clinical

classification was created in the year

1997 which is as follows;

CLASS 1:

a)Any ocular muscle weakness

b)May have weakness of eye closure

c)All other muscle strength is normal

CLASS II:

a)Mild weakness affecting other than ocular muscles

b)May also have ocular muscle weakness of any severity

CLASS 11 a:

a)Predominantly affecting limb, axial muscles, or both

b)May also have lesser involvement of oropharyngeal muscles

CLASS II b:

a)Predominantly affecting oropharyngeal, respiratory muscles, or both

b)May also have lesser or equal involvement of limb, axial muscles, or both

CLASS III:

a)Moderate weakness affecting other than ocular muscles

b)May also have ocular muscle weakness of any severity

CLASS III a:

a)Predominantly affecting limb, axial muscles, or both

b)May also have lesser involvement of oropharyngeal muscles

CLASS III b:

a)Predominantly affecting oropharyngeal, respiratory muscles, or both

b)May also have lesser or equal involvement of limb, axial muscles, or both

CLASS IV

a)Severe weakness affecting other than ocular muscles

b)May also have ocular muscle weakness of any severity

CLASS IV a

a)Predominantly affecting limb and/or axial muscles

b)May also have lesser involvement of oropharyngeal muscles

CLASS IV b:a)Predominantly affecting oropharyngeal,

respiratory muscles, or both

b)May also have lesser or equal involvement of limb, axial muscles, or both

CLASS V:

a)Defined by intubation, with or without mechanical ventilation, except when used during routine postoperative management.

b)The use of a feeding tube without intubation places the patient in class IVb.

1)TENSILON(edrophonium)TEST:edrophonium 10 mg is injected as iv improvement in weakness within seconds and last for 2- 3 minutes when test is positive.

2)Serum acetylcholine receptor antibodies: raised

3)CPK: Normal

4)ESR: Not raised

5)Antibodies to striated muscle: Present

5)Antinuclear antibodies & rheumatoid factor: positive

6)NERVE STIMULATION TEST: characteristic decrement in the evoked muscle action potential.following continuous stimulation of motor nerve

7)CXR: may show thymoma

1)Oral anticholinesterases like pyridostigmie is given.drug prolongs the action of Ach by inhibiting the action of cholinesterases( adverse effect can becolic,diarrhoea )

2)Immunosuppressant drugs like corticosteriods like azathioprine are used when there is incomplete response to anticholinesterases.thereis improvement in 70% of cases.Mycophenolate is a newer immunosuppressive drug having less adverse effects then steroids.

3)Thymectomy: for malignant tumor

4)Plasmapheresis and intravenous immunoglobulins:usewhen there is respiratory involvement