Myasthenia Gravis

Question 1

Myasthenia gravis pathology

Answer 1

Autoimmune destruction of nicotinic ACh receptors on post-synaptic side of NMJ

Question 2

Myasthenia gravis presentation

Answer 2

Relapsing/increasing muscular fatigue with use, affecting muscle groups in order down body
Ptosis
Diplopia
Myasthenic snarl on smiling

Question 3

Myasthenia gravis tests

Answer 3

Anti-AChR antibodies in 90%, look for muscle-specific tyrosine kinase (MuSK) Abs if negative
Decremental muscle response to repetitive n. stimulation
CT to exclude thymoma

Question 4

Myasthenia gravis treatment

Answer 4

Pyridostigmine 60-120mg PO up to 6x daily
Prednisolone 10mg/2d for relapses, or azathioprine
Thymectomy even if no thymoma may help in younger pt <5 yr previous history

Question 5

Myasthenic crisis and how to treat

Answer 5

Severe weakness of resp muscles during relapse
Can be similar to cholinergic crisis from overtreatment with pyridostigmine >960mg/d but rare
Treat with plasmapheresis to remove AChR Abs or IVIg

Question 6

Lambert-Eaton myasthenic syndrome pathology

Answer 6

Abs to voltage-gated pre-synaptic Ca channels at NMJ

Can be paraneoplastic or autoimmune

Question 7

Lambert-Eaton myasthenic syndrome clinical features

Answer 7

Gait issues before eye signs
Autonomic involvement
Hyporeflexia + weakness which improves post exercise
Diplopia/resp muscle involvement rare
Similar EMG to MG but improves post-exercise

Question 8

Lambert-Eaton myasthenic syndrome treatment

Answer 8

Pyridostigmine

CXR/CT as symptoms may precede cancer by >4yrs