The Tensilon test is used to diagnose myasthenia gravis. Patients positive for the disease should show an improvement in muscular strength following administration of Tensilon - edrophonium - IV. Edrophonium is a very short acting anticholinesterase and therefore increases the effective amount of acetylcholine at the neuromuscular junction in patients with myasthenia gravis.
An easily quantifiable muscle group should be used where possible. Respiratory function is good, since it can be measured by the forced ventilatory capacity.
Care must be taken for cholinergic effects, such as bradycardia, abdominal cramps, diarrhoea. Patients can be loaded with atropine in advance of the test; it is then advisable to precede with a placebo - IV saline - and then a test dose of 1 to 2 mg. If there are no adverse effects, follow this with a further 5 to 6 mg. Measure the response over 1 minute. The response lasts no longer than 5 minutes.
It is advisable to have atropine to hand to counter the edrophonium and for there to be full resuscitative equipment. Many units would undertake this test under intensive care conditions.
This test is "not specific for myasthenia gravis: the Lambert-Eaton syndrome and congenital myasthenia can both give similar findings" (1).
- Newsom-Davis, J. (1993). Myasthenia gravis and the Lambert-Eaton myasthenic syndrome. Prescribers' Journal 33(5): 205-11.
Last reviewed 06/2021