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Practice Easily Missed?

Myasthenia gravis

BMJ 2012; 345 doi: http://dx.doi.org/10.1136/bmj.e8497 (Published 21 December 2012) Cite this as: BMJ 2012;345:e8497
  1. J Spillane, clinical research associate 1,
  2. E Higham, general practitioner partner2,
  3. D M Kullmann, professor of neurology1
  1. 1UCL Institute of Neurology, London WC1N3BG, UK
  2. 2Central Medical Centre, Morden SM4 5RT, UK
  1. Correspondence to: J Spillane jennifer.spillane.09{at}ucl.ac.uk

A previously well 78 year old man presented to his general practitioner with a six month history of double vision that was more pronounced when he was tired. His wife had also noted drooping of his eyelids towards the end of the day. Examination showed restricted eye movements (ophthalmoplegia) and fatigable ptosis. He was referred to his local neurology centre and a diagnosis of myasthenia gravis was confirmed with antibody and electrophysiological tests. A computed tomography scan of his thorax was normal and he was prescribed oral pyridostigmine.

What is myasthenia gravis?

Myasthenia gravis is an autoimmune disorder of neuromuscular transmission characterised by fatigable muscle weakness. The disorder is typically mediated by antibodies against the postsynaptic acetylcholine receptor or by antibodies against muscle specific tyrosine kinase. About 10% of patients with myasthenia gravis have a thymoma.1 Any muscle group can be affected in myasthenia gravis, but typically patients present with ocular symptoms, namely diplopia and ptosis. Weakness then becomes generalised in about 80% of patients.2 The most serious complication is myasthenic crisis: acute respiratory failure resulting from myasthenia gravis that requires mechanical ventilation. Myasthenic crisis occurs in about 20% of patients with myasthenia gravis and is a neurological emergency requiring admission to an intensive care unit for respiratory support.3

How common is myasthenia gravis?

  • The prevalence of myasthenia gravis in the United Kingdom is estimated at about 15 per 100 000 population, although this figure has increased over time4 5

  • The incidence is bimodal, with a female:male ratio of 2:1 in younger adults and a reversed sex ratio in older people6

  • Both the incidence and the prevalence of myasthenia gravis in older patients are greater than previously thought7

Why is myasthenia gravis missed?

The fluctuating nature of the symptoms and the often subtle findings on clinical examination can make myasthenia gravis difficult to diagnose. In one study, diagnosis was …

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