Myasthenia gravis (MG) is caused by failure of chemical transmission at the 
neuromuscular junction. It is an autoimmune disorder in which antibodies 
interfere with neuromuscular transmission. It has a prevalence of around 20 per 
100,000. The incidence is bimodal with a 2:1 female to male ratio in the younger 
population and a reversed sex ratio over the age of 60. Around 15% of cases are 
associated with a thymoma. MG presents with fatiguable painless muscle weakness. 
Diplopia and ptosis are the most common presenting features. Around 80% of 
patients presenting with ocular MG will subsequently develop more generalised 
weakness. Respiratory muscle weakness is the most serious manifestation of MG 
and can be fatal. A detailed history is the most valuable tool in the diagnosis 
of MG. This should elicit the pattern of weakness, severity and diurnal 
variation. Exacerbating factors including extremes of weather, emotional stress, 
menstruation and intercurrent illness should be enquired about. No one 
diagnostic test is 100% sensitive and patients who have negative antibodies and 
normal neurophysiology may still have MG. Treatment should be directed at 
ameliorating weakness with acetylcholinesterase blockers and modulating the 
immune system. Pyridostigmine is the most widely used acetylcholinesterase 
inhibitor. Most patients with generalised MG require immunomodulatory therapy 
and prednisolone is generally used as the first-line agent. Despite the 
availability of symptomatic and immunomodulatory treatment, up to 20% of 
patients will experience a myasthenic crisis requiring admission for ventilatory 
support at some stage.