MYASTHENIA GRAVIS

1. Topic: MYASTHENIA GRAVIS
By : Vinayak U Navalihiremath
Moderator:
Dr. Sechassayanan AP
Department of general
medicine

2. Myasthenia gravis
• Myasthenia gravis (MG) is a neuromuscular
junction (NMJ) disorder characterized by
weakness and fatigability of skeletal muscles.

3. • The underlying defect is a decrease in the
number of available acetylcholine receptors
(AChRs) at NMJs due to an antibody-mediated
autoimmune attack

4. Incidence and Prevalence
• It affects individuals in all age groups
• Peak incidences occur in women in their
twenties and thirties and in men in their fifties
and sixties.
• Overall, women are affected more frequently
than men, in a ratio of ~3:2.

5. Etiology
• Most commonly by anti-AChR antibodies at
NMJs by three distinct mechanisms:
(1) accelerated turnover of AChRs
(2) damage to the postsynaptic muscle
membrane
(3) blockade of the active site of the AChR

6. • Anti-MuSK antibody occurs in about 10% of
patients (about 40% of AChR antibody negative
patients)
• 1–3% have antibodies to another protein at the
NMJ—low-density lipoprotein receptor-related
protein 4 (LRP4)—that is also important for
clustering of AChRs.
• Thymic abnormalities

7. Pathophysiology
Depolarization spreads. causing muscle contraction.
ACh receptor sites in motor end plates depolarize muscle fiber
ACh diffuses across synapse
Acetylcholine (ACh) is released.
Motor nerve impulses travel to motor nerve terminal
NORMAL NEUROMUSCULAR TRANSMISSION

8. Depolarization and muscle contraction don't occur. Neuromuscular transmission is blocked.
ACh receptor sites, weakened or destroyed by attached antibodies. block ACh
reception
ACh diffuses across synapse
Acetylcholine (ACh) is released
Motor nerve impulses travel to motor nerve terminal
NEUROMUSCULAR TRANSMISSION IN MYASTHENIA GRAVIS

10. Symptoms
• Babies with neonatal MG may be weak, with a
poor suck, and may have respiratory difficulty.
A few babies may need the help of a
mechanical breathing machine if their
respiratory muscles are too weak to breathe on
their own.
• Congenital MG symptoms may begin in the first
year, with generalized weakness in the arms
and legs, and delays in motor skills such as
crawling, sitting, and walking

11. • Juvenile MG symptoms may begin gradually over
weeks or months. The child may become
excessively tired after very little activity, and begin
to have problems chewing and swallowing.
Drooping eyelids may be so severe that the child
cannot see.
• Ocular MG If weakness remains restricted to the
EOMs for 3 years, it is likely that it will not become
generalized, and these patients are said to have
ocular MG

12. Eye muscles
In more than half the people who develop MG,
their first signs and symptoms involve eye
problems:
• Drooping of one or both eyelids (ptosis)

13. • Double vision (diplopia), which may be
horizontal or vertical
• Blurred vision, which may come and go

14. Face and throat muscles
In about 15 percent of people with myasthenia
gravis, the first symptoms involve face and throat
muscles, which can cause difficulties with:
• Speaking. The speech may be very soft or sound
nasal, depending upon which muscles have been
affected.
• Swallowing. May choke very easily, which makes
it difficult to eat, drink or take pills. In some cases,
liquids may come out of the nose.

15. • Chewing. The muscles used for chewing may
wear halfway through a meal, particularly if
eating something hard to chew, such as
sugarcane.
• Facial expressions. Family members may note
"lost smile" if the muscles that control facial
expressions are affected.

16. Arm and leg muscles
• Myasthenia gravis can cause weakness in
arms and
legs, but this usually happens in conjunction
with muscle weakness in other parts of the
body - such as eyes, face or throat.
• The disorder usually affects arms more often
than
legs.
• If it affects legs, may waddle when walking.

18. THANK YOU