Myesthenia Gravis

Question 1

Aetiology

Answer 1

• autoimmune
• antibodies prevent acetylcholine binding
• maintains striated muscle contracture - fatigue

Question 2

Features of ocular MG

Answer 2

• 40/50% of ocular MG Px have antibodies
• can be associated with systemic disease
• symptoms get worse throughout the day
• ptosis
• diplopia
• inadequate lid closure

Question 3

Features of ptosis in MG

Answer 3

• usually first presenting sign
• bilateral but asymmetrical
• ptosis increases throughout the day

Question 4

Measurement in ptosis

Answer 4

• ptosis should increase on continued elevation
• positive Cogan’s twitch
• fluttering upper lid
• holding most effected lid open, contralateral ptosis increases
• frontialis overaction can cause upper lid retraction

Question 5

Diplopia in MG

Answer 5

• horizontal/vertical/both - will vary during day
• MG can mimic any type of muscle palsy
• obicularis weakness

Question 6

Systemic signs

Answer 6

• difficulty swallowing and chewing
• difficulty speaking
• breathlessness
• fatigue climbing stairs or holding arms up
• lack of facial expression
• fatal if Lungs involved
• excessive fatigue on striated muscle
• 80/90% of general MG Px have antibodies in blood

Question 7

Investigations

Answer 7

• ice pack test
• lowering temp can improve symptoms
• ice pack test improves ptosis
• sleep test
• lid position will improve if MG
• blood test, acetylcholine receptor site antibodies
• tension test, short acting anticholinesterase

Question 8

Management - General

Answer 8

• possible longer acting anticholinesterase
• CT scan of thymus gland
• if enlarged then remove
• systemic steroids - prednisolone

Question 9

Ocular management

Answer 9

• fresnel prism
• ptosis props
• occlusion
• Botox
• strabismus surgery