Part 2 · Diagnosis
MGFA class & scores
The MGFA clinical classes I to V, the post-intervention status, and the MG-ADL, QMG and MG Composite scores. Press play to follow a schematic patient across the classes over months, then score the MG-ADL yourself.
A schematic course, not a real patient and not a typical one. Class wording is the MGFA's own; click a class on the ladder to read it.
Class V and the breathing mask: two definitions
Class V: "Defined as intubation, with or without mechanical ventilation, except when employed during routine postoperative management. The use of a feeding tube without intubation places the patient in class IVb."
Non-invasive ventilation is not mentioned. Read strictly, a person kept off a ventilator by a BiPAP mask is not Class V. 271,354
Manifest myasthenic crisis: MGFA Class V, meaning worsening of myasthenic weakness "requiring intubation or noninvasive ventilation to avoid intubation".
The same label now covers people treated with a mask. Claytor and colleagues likewise define crisis as respiratory insufficiency needing invasive or non-invasive ventilation. 82,476
Why the gap matters: in a Mayo series of 60 crisis episodes, BiPAP was the first support in 24 and intubation was avoided in 14 of them (about 58%); in the first BiPAP series it was avoided in 7 of 11 trials. Under the 2000 wording those people would stay in IVb; under the 2016 definition they are Class V. Counts of "Class V" or "crisis" in different studies may therefore not mean the same thing. 437,476,486 Trouble breathing or swallowing in MG is an emergency; see Myasthenic crisis.
The MGFA classes, word for word
| Class | Published wording |
|---|---|
| I | "Any ocular muscle weakness; may have weakness of eye closure. All other muscle strength is normal." |
| II | "Mild weakness affecting muscles other than ocular muscles; may also have ocular muscle weakness of any severity." |
| III | "Moderate weakness affecting muscles other than ocular muscles; may also have ocular muscle weakness of any severity." |
| IV | "Severe weakness affecting muscles other than ocular muscles; may also have ocular muscle weakness of any severity." |
| a (IIa, IIIa, IVa) | "Predominantly affecting limb, axial muscles, or both. May also have lesser involvement of oropharyngeal muscles." |
| b (IIb, IIIb, IVb) | "Predominantly affecting oropharyngeal, respiratory muscles, or both. May also have lesser or equal involvement of limb, axial muscles, or both." |
| V | "Defined as intubation, with or without mechanical ventilation, except when employed during routine postoperative management. The use of a feeding tube without intubation places the patient in class IVb." |
Wording from the MGFA clinical classification 271,354. The class describes the disease at that examination; the 2025 MGFA task force says it should be updated every 3 to 6 months 469.
Post-intervention status
| Status | Definition (MGFA-PIS) |
|---|---|
| Complete stable remission (CSR) | No symptoms or signs of MG for at least 1 year and no MG therapy during that time; no weakness of any muscle on careful examination by someone skilled in neuromuscular evaluation. Isolated weakness of eyelid closure is accepted. |
| Pharmacologic remission (PR) | The same criteria as CSR, except the patient continues some form of MG therapy. Patients taking cholinesterase inhibitors are excluded, because their use suggests weakness. |
| Minimal manifestations (MM) | No symptoms of functional limitation from MG, but some weakness on examination of some muscles. MM-0: no MG treatment for at least 1 year. MM-1: continuing immunosuppression, no cholinesterase inhibitors or other symptomatic therapy. MM-2: only low-dose cholinesterase inhibitors (under 120 mg pyridostigmine a day) for at least 1 year. MM-3: cholinesterase inhibitors or other symptomatic therapy plus some immunosuppression during the past year. |
| Improved (I) | A substantial decrease in pre-treatment manifestations, or a sustained substantial reduction in MG medications; in prospective studies, a specific decrease in QMG score. |
| Unchanged (U) | No substantial change. |
| Worse (W) | A substantial increase in manifestations or in MG medications. |
| Exacerbation (E) | A patient who met CSR, PR or MM criteria and then developed findings beyond those criteria. |
| Died of MG (D of MG) | Death from MG, from complications of therapy, or within 30 days after thymectomy. |
271,355 The 2016 consensus excludes from remission anyone taking a cholinesterase inhibitor every day with reasonable evidence of benefit, and calls MG refractory when PIS is unchanged or worse after corticosteroids and at least 2 other immunosuppressive agents at adequate dose and duration. 476
Over the past year, on careful examination:
MG treatment during that time:
Has this lasted at least 1 year?
Applies the MGFA-PIS definitions word by word. The 2025 MGFA task force describes PIS as the evaluator's overall clinical judgement, which needs no defined change on any score. 355,469
MG-ADL, scored live
The MG Activities of Daily Living profile has 8 items scored 0 to 3: 2 ocular, 3 oropharyngeal, 1 respiratory and 2 extremity items, for a total of 0 to 24. Current MGNet instructions: the person completes it, rating their average function over the last 7 days, taking their current MG medicines into account and counting only symptoms from MG. If torn between two scores, record the higher. 351,356,551
Anchor wording from the MG-ADL form (© 1997 UT Southwestern) 351,551. Thresholds: 2-point improvement 369; minimal symptom expression 0 or 1, PASS threshold 2, and a floor effect, as collected by MGNet 359. The examples are invented. Not a clinical tool.
The other scales
QMG (Quantitative MG score)
13 items, each 0 (none) to 3 (severe), total 0 to 39: diplopia on lateral gaze, ptosis on upward gaze, facial muscles, swallowing, speech, right and left arm outstretched, forced vital capacity, right and left hand grip, head lift, right and left leg outstretched. It takes about 20 to 30 minutes and needs a spirometer, a stopwatch and a dynamometer. 358,359
Meaningful change: at least 2 points if baseline QMG is 0 to 16, at least 3 if above 16; other estimates 2.3 and 2.6. The individual minimum detectable change, 4.3, may exceed the MCID. 32,37,285,359
MG Composite
10 items with weighted scoring, maximum 50. A 3-point improvement was optimal for signifying clinical improvement in 175 patients at 11 centres, and test-retest reliability was 98%. 65,66,357 The weights put breathing highest:
Diplopia within 1–10 s scores 3 but ptosis in the same time scores 2. Limb grades: mild is MRC 4+, moderate 4 to 4−, severe 3 or less. 65,357
MG-QOL15r
The MG-QOL15 was revised after Rasch analysis of more than 1,300 surveys: 3 items were reworded and a 3-response format worked best. It is the preferred quality-of-life instrument. With 15 items scored 0 to 2, the range is 0 to 30, a figure inferred from the item structure rather than stated in the abstract. 67
Meaningful change: anchored to the MG-ADL in ADAPT (157 people) and MyRealWorld-MG (92), the MCID ranged from 1.6 to 3.0; the authors suggest 2- and 3-point thresholds. 41
How the MG-ADL holds up
In the original 254 encounters, mean MG-ADL was 4.89 and mean QMG 10.80, with a correlation of 0.583. In 87 patients the MG-ADL correlated with the MG Composite at r = 0.85, and a 2-point improvement indicated clinical improvement. An MG-ADL of 0 or 1, "minimal symptom expression", is used as a trial endpoint. 359,369,551