Myasthenia Gravis
Myasthenia Gravis is a Latin term meaning Grave Muscle Weakness
Definition:-
MG is an autoimmune disorder affecting the myoneural junction (also called
neuromuscular junction) and is characterised by varying degrees of weakness of voluntary
muscles
The weakness of skeletal muscles worsens upon exertion and improves after rest
periods. Myasthenia gravis results from failure or error in transmission of impulses between
nerves and muscles. Although it is a relatively rare condition, myasthenia gravis can affect
people of all ages, and is most commonly seen in women younger than 40 years old and in
men above 60 years old.
At present, there is still no cure for myasthenia gravis, but treatment aims in
relieving signs and symptoms and improving the patient's quality of life.
Causes:-
Autoantibodies directed at acetylcholine receptors:
Muscles and nerves communicate through neurotransmitters, which are chemicals
released by the nerves and matches into the receptor sites found in the neuro-muscular
junction. When a continuous problem in this process of transmission occurs, myasthenia
gravis can develop. The immune system blocks the receptor sites for a neurotransmitter
called acetylcholine by producing antibodies. Less receptor sites cause insufficient
acetylcholine secretion and fewer nerve signals result in muscle weakness. These antibodies
also block protein function and tyrosine kinase, a protein enzyme associated in the
formation of neuro-muscular junction.
• Thymus gland may trigger and maintain levels of antibodies that block acetylcholine
receptors
• It is also associated with thymus tumours
• There is also a type of myasthenia gravis that is antibody-negative, wherein the root
cause is the antibodies are working against Lipoprotein-related protein 4, and not by
blocking the acetylcholine.
Clinical manifestations:-
•Muscle weakness with activity- hallmark sign
• Ocular myasthenia - weakness of the eye muscles
• Ptosis -drooping of one or both eyelids
• Diplopia - double vision
