What are the most common diagnostic tests for Myasthenia Grevis?
The diagnosis of Myasthenia Grevis is a clinical one but may be supported by several different tests.
Electrophysiologic tests are often the first step after clinical examination, and typically include repetitive nerve stimulation (RNS) studies, which have a sensitivity of 40% to 90% depending on disease severity.
A more advanced test, single-fiber electromyography (SFEMG), is the single most sensitive assay in Myasthenia Grevis with a sensitivity of 90% to 95% even in mildly symptomatic patients.
The AChR binding antibody assay (using serum samples) is 90% sensitive in generalized disease and 70% in pure ocular disease, but the blocking and modulating AChR antibody assays are less sensitive, particularly in pure ocular disease.
Administration of the short-acting AChE inhibitor edrophonium (the Tensilon test) may transiently improve strength and can also aid in diagnosis but must be properly performed in a patient having clearly discernible weakness on examination to serve as a gauge for response.
