The masquerade of myasthenia gravis

Published Date: 19th July 2016

Publication Authors: Mavinamane S

Objective

Myasthenia gravis is an autoimmune condition characterised by fatigable muscle weakness. It may present as a bulbar palsy and can mimic a cerebrovascular event. We report a case of myasthenia gravis presenting in a 69 year old which initially presented as stroke.

Case presentation

A 69 year old male was admitted to a hospital with a sudden onset of difficulty in swallowing and slurred speech which started two weeks prior to admission. Past medical history included type 2 diabetes mellitus, hyperlipidaemia, hypertension, and gout and the patient was an ex-smoker. Full neurological examination was normal except for mild dysarthria and difficulty in swallowing. Routine blood tests, electrocardiogram, CT brain, echocardiogram and carotid Doppler's were all normal. An initial diagnosis of stroke was considered due to his risk factors and the patient was started on Aspirin 300 mg. Assessment by a speech and language therapist revealed poor swallow but the patient tolerated a modified diet. Otherwise he was independently mobilising and self-caring. Over a few days, there was no improvement in his dysarthria and dysphagia. An MRI with diffusion weighted imaging showed patchy high signal changes, likely to be ischaemic but no acute infarct. On further assessment, fatigability was demonstrated with prolonged speech and it was noted that the patient had difficulty chewing. However, there was no ptosis and no obvious limb fatigability. The diagnosis of stroke was revisited and myasthenia gravis was considered. The patient underwent neurophysiological investigations and single fibre electromyography was positive. In addition, acetylcholine receptor antibodies were positive (titre 19 nmol/l [> 0.4 nmol/l is abnormal]). A CT thorax did not reveal a thymoma. The patient was started on pyridostigmine and steroids in addition to five days of intravenous immunoglobulin with a significant clinical improvement.

Discussion and conclusion

Myasthenia gravis is an autoimmune disorder of neuromuscular transmission associated with acetylcholine receptor antibodies. Diagnosis in the elderly can be difficult due to multiple co-morbidities and vague symptoms. It has been reported that 59% of all patients with myasthenia are elderly. This clearly overlaps with a patient group most at risk of cerebrovascular disease and therefore correct diagnosis is important. In this case, stroke was considered primarily due to a relatively acute onset of symptoms and a significant vascular history. In addition, the patient did not have ocular features, muscle fatigability or respiratory problems. This report describes a case of myasthenia gravis masquerading as a stroke in a patient with a significant vascular history. Accurate diagnosis of stroke is increasingly important where rapid decisions regarding thrombolysis are made. As such, myasthenia gravis should be considered as a differential in elderly patients presenting with bulbar symptoms as prompt diagnosis may prevent complications of this treatable disease.

Piercy, HL; Hamilton, DO; Mavinamane, S. (2013).  The masquerade of myasthenia gravis . European Journal of Internal Medicine. 24 (Supp 1), e50-51

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