Myasthenia gravis

Question 1

What is Myasthenia Gravis?

Answer 1

Myasthenia gravis (MG) is a chronic autoimmune disorder of the post-synaptic membrane at the neuromuscular junction (NMJ) in skeletal muscle.

Circulating antibodies against the nicotinic acetylcholine receptor (AChR) and associated proteins impair neuromuscular transmission.

Question 2

What are the signs and symptoms of Myasthenia Gravis?

Answer 2

Characterised by muscle weakness that increases with exercise (fatigue) and improves on rest.

Commonly presents with drooping eyelids, double vision, oropharyngeal and/or appendicular weakness, and shortness of breath.

Also:
> Dysphagia

Question 3

What are the risk factors of Myasthenia Gravis?

Answer 3

FHx of AI disease
Genetic markers
Cancer targeted therapies

Question 4

What is the epidemiology of Myasthenia Gravis?

Answer 4

Myasthenia gravis (MG) is an uncommon disease with an estimated worldwide prevalence of 100 to 200 per million population.

Question 5

What investigations would you do for Myasthenia Gravis?

Answer 5

> Serum AChR antibody analysis
muscle specific tyrosine kinase antibodies
Serum pulmonary function tests
Repetitive nerve stimulation

Results:
Elevated serum acetylcholine receptor antibody titres or muscle-specific tyrosine kinase antibodies are present.

Antibodies to 4 new autoantigens, low-density lipoprotein receptor-related protein (LRP4), agrin, collagen Q, and cortactin, located at the neuromuscular junction, have been identified.

Clinical electrophysiology shows decremental response on repetitive nerve stimulation or increased jitter on single-fibre study.