Myasthenia gravis is said to be a clinically obvious disease which does not normally require laboratory tests, however, there are many laboratory tests that can be done to confirm myasthenia gravis. Endrophonium chloride is a short acting anticholinesterase. This is not effective in cats, however, because they do not react predictably to the short acting anticholinesterase endrophonium chloride. Animals that are not already collapsed are made to do some type of exercise until weakness develops. After the exercise, the animal is given an injection of the anticholinesterase endrophonium chloride.
Muscle strength following the injection of endrophonium chloride is evaluated.
With a positive test, muscle strength improves within 10 - 30 sec after injection and decreases within 5 minutes. If no benefit is seen after 2 minutes, the test is negative. This test is not specific only for myasthenia gravis and other tests should be performed to confirm the disease. Other tests can be done in the same fashion as the endrophonium chloride response test using longer acting anticholinesterase drugs such as neostigmine methylsulfate. Clinical improvements occur 15 - 30 minutes after the injection.