In addition to a complete medical and neurological evaluation, a number of tests may be used to establish a diagnosis of MG. A characteristic of MG is that patients have weakness that comes on with activity and improves following rest. To examine for weakness with activity, a clinician might have a patient do a sustained task, such as looking upwards (which induces the eyelids to remain elevated) to see if the eyelids start to droop (referred to clinically as ptosis) when the eyelids are open for several minutes. To test for recovery of strength after rest, a clinician may examine muscle strength and then have the patient suspected to have MG rest or rest a part of the body and then retest muscle strength after rest to see if strength improves. For example if a person who is suspected to have MG has droopy eyelids, the physician might have the patient lay down with his/her eyes closed for several minutes, perhaps with a cool pack over the eyelids, to see if eyelid function improves after rest.
A diagnosis can be confirmed in several ways, including the following:
Sometimes all of these tests are negative or equivocal in someone whose story and examination still seem to point to a diagnosis of MG. A clinician skilled in recognizing MG and distinguishing MG from other conditions would need to determine if such a patient has MG or another disorder.
Reviewed by the MGFA’s Medical Advisory Board, November 2010