Ocular manifestations of systemic disease: Myasthenia gravis

Question 1

What is myasthenia gravis?

Answer 1

Autoimmune condition with Ab targeting post-synaptic Ach receptors on NMJ of skeletal muscles resulting in painless weakness that worsens with activity and improves with rest (fatigable)

Question 2

Ocular signs of myasthenia gravis

Answer 2

• Asymmetrical, bilateral ptosis which is pupillary sparing a/w frontalis muscle overactivity to compensate for ptosis
• Ptosis that gets worse at the end of the day
• Diplopia
• Fatigability with sustained upgaze (Simpson test)
• Cogan’s lid twitch
• Curtain’s sign
• Peek sign

Question 3

Cardinal features of MG

Answer 3

Fatigability
Variable
Reversible with rest

Question 4

Symptoms/signs of MG

Answer 4

• Extraocular muscles: Ptosis, Diplopia (often first symptoms)
• Bulbar muscles: dysarthria, difficulty swallowing, difficulty chewing, dysphonia
• Facial muscles: facial droop
• Truncal muscles: respiratory failure
• Limb muscles: generalized proximal weakness
• Weakness in neck flexion

Question 5

Investigations for MG

Answer 5

Bedside
- Ice pack test (ptosis improves)
- Tensilon test

Bloods
- Anti-acetylcholine receptor antibody (80% in generalized MG, 50% in ocular MG)
- Anti-Muscle Specific Kinase antibody
- Anti striated muscle antibody
- FBC, RP, TFT

Imaging
- CXR
- CT thorax

Electrodiagnostic studies
- Repetitive nerve stimulation test
- Single fibre nerve electromyography

Question 6

Management of MG

Answer 6

Conservative
- Patient education: avoid triggers, red flag sx, compliance to meds
- Referral to OT/PT for mobility issues, ST for swallowing impairment
- Diplopia: Occlusion/ Patch, Prisms
- Ptosis: Lid Crutches/ Taping

Medical
- PO pyridostigmine/neostigmine
- Corticosteroids
– 2nd line: Azathioprine, mycophenalate mofetil, cyclosporin, tacrolimus
- For myasthenic crisis: Plasmapheresis, IVIG

Surgical
- Thymomectomy