Myasthenia gravis Flashcards
What is Myasthenia Gravis?
An autoimmune disease mediated by antibodies to nicotinic acetylcholine receptors (AChR) on the post-synaptic side of the neuromuscular junction
Describe the presentation of MG
Slowly increasing or relapsing muscular fatigue
Muscle groups affected in order - extraocular, bulbar (swallowing and chewing), face, neck, limb girdle, trunk
What are the signs of MG
Ptosis Diplopia Myasthenic snarl on smiling Peek sign of orbicularis fatigability Dysphonia - on counting to 50 voice fades (rare) Tendon reflexes are normal
What are MG symptoms exacerbated by?
Infection Emotions Environment Pregnancy Hypokalaemia Over-treatment Exercise Drugs - gentamicin, opiates, tetracycline, quinine, betablockers
What is MG associated with?
RA
SLE
Thymic hyperplasia (women <50)
Thymic atrophy or tumour (men >50)
What investigations would you request for MG
Antibodies - AntiAChR (anti-acetylcholine receptor antibodies) or MUSK antibodies (muscle specific tyrosine kinase)
EMG - decremental muscle response to repetitive nerve stimulation +/- single fibre jitter
Imaging - CT to exclude thyoma
Ice application - improves ptosis >2mm after 2 mins
Describe the treatment of MG
Symptom control - acetylcholinesterase - pyridostigmine
Immunosuppression - prednisolone for relapses, azathioprine, ciclosporin and mycophenolate mofetil may be used
Thymectomy
List the side effects of pyridostigmine
Cholinergic SE - hypersalivation, lacrimation, sweats, vomiting and miosis
Other - diarrhoea, colic
What is a myasthenic crisis?
Life threatening weakness of respiratory muscles during a relapse
What can myasthenic crisis be difficult to differentiate from?
Cholinergic crisis (overtreatment of MG - rare and usually doses >960mg/d of pyridostigmine)
How is a myasthenic crisis managed?
Monitor Forced vital capacity
Ventilatory support may be needed
Treat with plasmapheresis or IVIg
Identify and treat the trigger for the relapse
