Patient-acceptable symptom states in myasthenia gravis.

Objectives: To estimate patient-acceptable symptom state (PASS) cut points for myasthenia gravis (MG) health scales.

Methods: We conducted an electronic survey that included the Myasthenia Gravis Impairment Index (MGII), EuroQol 5-Dimension (EQ5D), and a simple PASS question. PASS-anchored thresholds were estimated for the MGII questionnaire through receiver operating characteristic curves. We used the MGII PASS cut point in a validation cohort of 257 patients to estimate PASS thresholds for other clinically relevant health scales such as the Quantitative Myasthenia Gravis Scale (QMGS), Myasthenia Gravis Activities of Daily Living (MG-ADL), Myasthenia Gravis Composite (MGC), and Myasthenia Quality of Life (MG-QoL15).

Results: One hundred twenty-four of ≈250 invited patients answered the electronic survey (49% response rate), and 80 considered their current symptom state acceptable (PASS-positive). They had lower MGII scores than PASS-negative patients (7.76 ± 9.37 vs 25.0 ± 13.7, < 0.0001) and better EQ5D scores (0.86 ± 0.17 vs 0.69 ± 0.18, < 0.0001). The MGII questionnaire threshold for PASS was ≤10 points. With the use of this threshold in an independent dataset of 257 patients, all patients in remission or minimal manifestation status were PASS-positive. In addition, some patients in Classes I, II, and IIIA also achieved PASS status. PASS thresholds for the QMGS, MG-ADL, MGC, and MG-QoL15 were ≤7, 2, 3, and 8 points, respectively.

Conclusions: We have estimated thresholds for commonly used myasthenia health scales reflecting patient-acceptable states in patients with MG. These thresholds indicate a global state of well being, rather than a change in scores, or being better. Therefore, PASS thresholds can be used as secondary endpoints for myasthenia research.