Evidence for comparative effectiveness of immunosuppressive/ immunomodulating (IS/IM) treatments for myasthenia gravis (MG) is not available.

To present baseline data of participants in the PROMISE-MG study.

Multicenter, prospective, observational comparative effectiveness study comparing outcomes at 2 years in: 1. MG patients who receive azathioprine (AZT) vs. mycophenolate (MMF), 2. Patients receiving vs. not-receiving AZT/MMF at adequate doses/duration.

Inclusion criteria: autoimmune MG, age >18 years, no IS/IM treatment prior to initial study visit. Patients are treated as in routine clinical practice. Co-primary outcomes are MGQOL-15r, and a composite measure of achieving Minimal Manifestation status with no more than grade 1 CTCAE adverse effects.

De-identified data are entered into a central REDCap database. We used descriptive statistics to analyze initial visit data and Pearson correlation to measure the association between outcome measures.

One hundred sixty seven participants are enrolled from 19 centers: male 62%, 93% Caucasian. Average age at disease onset: 63±14 years (females 61± 17, males 65±11). Sixty percent have generalized MG. MGFA class: I - 40%, II - 37%, III - 20%, IV/V - 3%. Mean disease duration: 1.2± 2.4 years; 76% are AChR-Ab positive, 5% MuSK-Ab positive. Thymus imaging: normal/involuted - 88%, thymoma - 7%. At initial visit, 57% were on pyridostigmine. Treatment was started or changed in 73% (66% pyridostigmine, 23% corticosteroids).  Mean outcome measure scores at initial visit: MGQOL15r - 10.9±8.2, MG Composite (MGC) - 8.6±6.3, MG-MMT - 8.3±6.8, MG-ADL - 5.5± 3.3. Correlations between outcome measures were strong (r= 0.71 to 0.79) for MGC/MG-ADL and MGC/MG-MMT; all other measures correlated moderately with each other (r= 0.54 to 0.68), all p< 0.0001.

Participants in PROMISE-MG are predominantly male with disease onset in the 7^th decade.  The highest correlations among outcome measures were between MGC/MG-ADL and MCC/MG-MMT, likely because the MG-ADL and MG-MMT are components of the MGC.

 Dr. Narayanaswami and Dr. Sanders are co-PIs and contributed equally