The MG composite: an outcome measure for myasthenia gravis for use in clinical trials and everyday practice.

The myasthenia gravis composite (MGC) was constructed by selecting the best performing items from three commonly used, MG-specific scales. The response categories of the items were subsequently weighted for importance. The MGC, which takes less than five minutes to complete, is made up of three ocular, three bulbar, one respiratory, one neck, and two limb items. After its construction, the MGC was validated in an 11-center scale validity study. During the validation study, which included test-retest analysis, it was determined that a 3-point improvement in MGC score reliably indicates clinical improvement. A 3-point improvement in MGC also appears to be meaningful to the patient. Rasch analysis of the MGC confirmed that all 10 items belong and can be summed to provide a total score, and that the weights given to the response categories of the items are appropriate.