It is an autoimmune disease characterised by the weakness of the skeletal muscle
Autoantibodies are made to the nicotinic acetylcholine receptor in skeletal muscle
Transmission through the neuromuscular junction is decreased
Aetiology
Age
Different distribution between males and females
For females the peaks are between 20-30 years
For males - peaks are between 60-80 years
The risk is higher in younger females compared to males
Cause of the autoimmune disease is largely unknown
Signs and Symptoms
Usually patients present with ocular symptoms Usually patients present with ocular symptoms Usually patients present with ocular symptoms Usually patients present with ocular symptoms
drooping eyelids (ptosis)
Double vision (diplopia)
Restricted eye movements ( worse when tired)
Also includes - lack of facial expression, difficulties chewing Difficulty swallowing (dysphagia), weakness in arms, legs and neck, SOB - can be severe myasthenic crisis
Tests
Can be difficult to diagnose since symptoms can fluctuate
In older patients there are similarities to other conditions
Cause of the disease is largely unknown
Ice test
simple
cooling the muscle improves symptoms
Blood test for autoantibodies
Test 2
Neurophysiology
Electromyogram measures the muscle compound action potential in response to repeated stimulation
See a decrease in the size of the muscle response
Edrophonium test
Edrophonium is a short acting cholinesterase inhibitor
Injection of edrophonium causes increase in muscle strength (ptosis is reversed)
rarely used due to side effects
CAT scan used to exclude thymoma
Natural history
Long term condition
most patients can live normal lives without significant impact on life expectancy
Severity fluctuates
Usually starts with ocular symptoms
Then progresses to affect other muscles - progression can be rapid weeks or slow years
Can be life threatening - myasthenic crisis, affects 20% of patients at some point in their lives