What are the Myasthenia Gravis Foundation of America operational definitions of myasthenia gravis (MG)?

Updated: Aug 27, 2018
  • Author: Abbas Jowkar, MD; Chief Editor: Nicholas Lorenzo, MD, MHA, CPE  more...
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Answer

In October 2013, the Myasthenia Gravis Foundation of America appointed a Task Force to develop treatment guidance for MG. Definitions were developed for goals of treatment, minimal manifestation status (MMS), remission, ocular MG, impending crisis, crisis, and refractory MG. Guidance statements were developed for symptomatic and immunosuppressive treatments, IV immunoglobulin and plasma exchange, management of impending and manifest myasthenic crisis, thymectomy, juvenile MG, MG associated with antibodies to muscle-specific tyrosine kinase, and MG in pregnancy. [53]

MGFA Task Force defined goals of treatment of MG to achieve Minimal Manifestation Status (MMS) or better, with no more than grade 1 Common Terminology Criteria for Adverse Events (CTCAE) medication side effects. Operational definitions were set as follows:

Definition of remission: The patient has no symptoms or signs of MG. Weakness of eyelid closure is accepted, but there is no weakness of any other muscle on careful examination. Patients taking cholinesterase inhibitors (ChEIs) every day with reasonable evidence to support symptomatic benefit are therefore excluded from this category.

MMS: The patient has no symptoms or functional limitations from MG but has some weakness on examination of some muscles. This class recognizes that some patients who otherwise meet the definition of remission have mild weakness.

CTCAE grade 1 medication side effects: asymptomatic or only mild symptoms; intervention not indicated.

Definition of ocular MG (based on dysfunction due to MG at a specified point in time, and not dependent upon the duration of disease): MGFA Class I: Any ocular muscle weakness. May have weakness of eye closure. Strength in all other facial, bulbar, and limb muscles is normal. (It is recognized that some patients report fatigue when strength testing is normal. The physician should use clinical judgment in attributing fatigue to generalized MG in the absence of objective nonocular weakness).

Definition of impending myasthenic crisis: Rapid clinical worsening of MG that, in the opinion of the treating physician, could lead to crisis in the short term (days to weeks).

Definition of manifest myasthenic crisis (the concept of crisis focuses on the clinical implications—it represents a serious, life-threatening, rapid worsening of MG and potential airway compromise from ventilatory or bulbar dysfunction): MGFA Class V: Worsening of myasthenic weakness requiring intubation or noninvasive ventilation to avoid intubation, except when these measures are employed during routine postoperative management (the use of a feeding tube without intubation places the patient in MGFA Class IVB).

Definition of refractory MG: Unchanged or worse after corticosteroids and at least 2 other immunosuppressant agents, used in adequate doses for an adequate duration, with persistent symptoms or side effects that limit functioning, as defined by patient and physician


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