information about myasthenia gravis

1. ASSISMENT ON
MYASTHENIA GRAVIS
BY-NILESH SHARMA
(PHARM-D 2ND YEAR)

2. CONTENTS
1. DEFINATION.
2. MEACHANISM AND ITS EFFECTS.
3. DRUGS, RELATED THERAPIES AND TREATMENT.
4. DIAGNOSTIC TEST FOR MYASTHENIA GRAVIS.

3. DEFINATION.
• Mysthenia gravis is an autoimmune disorder affecting about 1 in 10,000 population ,due to
development of antibody directed to the Nicotinic Receptor (NR) at the muscle endplate.

4. MEACHANISM.
 The number of free Nm cholinoceptors may be reduced to 1/3 of normal or less
(fig7.3KDT) and structural damage to the neurotransmitter junction .
 This results in weakness and easy fatigability on repeated activity ,with recovery
after rest.
 The eyelid ,external ocular ,facial ,and pharyngeal, muscles are generally involved fist.
 Later limb and respiratory muscles get affected .

5. DRUGS, RELATED THERAPIES AND TREATMENT.
 Neostigmine and its congeners are the first line drugs are used to restore muscle strength.
 They improve muscles contraction and allowing Ach released from prejunctional endings to accumulate
and acts on receptor over a large area ,as well as by directly depolarizing the end plate.
 Treatment is usually started with neostigmine 15mg orally 6hr ,dose and frequency is them adjusted to
obtain relief from weakness.

6. CONT…
 Pyridostigmine is an alternative which needs less frequent dosing.
 If intolerable muscarinic side effects are produced ,atropine can be added to block them.
 Atropine has no effect on the basic disorder which often progresses ,ultimately it may not be possible to
restore muscle strength adequately with anti –CHEs alone.
 Thymectomy (surgical removal of thymus ) is now generally advised for patients with generalized
weakness particularly for those with a thymoma (tumor in thymus) and for younger patients .it is
effective in majority of cases .
 Thymectomy produces gradual improvement and even complete remission has been obtained .

7. CONT…
 Corticosteroids afford improvement in myasthenia gravis by their immunosuppressant action.
 They inhibit production of antibody to NR, and may inc synthesis of new NRs.
 However ,they are generally reversed for patients who do not respond adequately to anti –CHEs and
have failed after thymectomy or are unsuitable for it.
 However long term use of corticosteroids has problem of its own .
 Immunosuppressants like azathioprine and cyclosporine are also benificial in advance cases .
 Removal of antibody by plasmopheresis (plasma exchange ) is another approach .
 It may produces dramatic but often short –lived improvement in myasthenic crisis (it is characterized by
acute weakness of respiratory muscles )
 Overtreatment with anti –CHEs can cause myasthenia crisis and cholinergic crisis.

8. CONT….
 They can be differentiated by edrophonium test.

9. DIAGNOSTIC TEST FOR MYASTHENIA GRAVIS
A. Ameliorative test – Initally edrophonium 2mg is injected i.v as a test dose.
• If nothing untowed happens the remaining 8mg is injected after 30-60 sec .
• Reversal of weakness and short lasting improvement in the strength of affected muscles occurs in
myasthenia gravis and not in other muscles dystrophies .
B. Provocative test –myasthenics are highly sensitive to d- tubocurarine ;0.5 mg i.v causes marked
weakness in them, but ineffective in non- myasthenics . This test is hazaradus .
C. Demonstration of anti –NR antibodies in plasma or muscles biopsy specimen is a more reliable TEST.

10. THANK U.
• REFERANCES- KDT.