Current patient- and physician-reported measures of disease severity and clinical response effectively reflect rapid improvements associated with plasma exchange in myasthenia gravis (MG) patients, a study reports.
These findings support the use of these MG-specific outcome measures in clinical trials of rapidly effective therapies for MG, such as plasma exchange and intravenous immunoglobulin infusion (IVIG).
The study, “Clinical outcome measures following plasma exchange for MG exacerbation,” was published in the journal Annals of Clinical and Translational Neurology.
In people with MG, the body’s immune system mistakenly recognizes the acetylcholine receptor (AChR) — a cell membrane protein essential for nerve-muscle cell communication — or the muscle‐specific tyrosine kinase receptor (MuSK), as foreign molecules and attacks them by producing autoantibodies against these molecules. This leads to muscular weakness, lack of muscle control, and fatigue.
Long‐term therapies for MG include removal of the thymus (thymectomy), anticholinesterases, and immunosuppressive or immunomodulatory treatments. Rapidly (though temporary) effective treatments — including plasma exchange and intravenous immunoglobulin infusion (IVIG) — are usually given to patients with very severe exacerbations (symptom worsening), who do not respond well to other treatments, or who are about to undergo surgery.
Current validated measures to assess disease severity and clinical response include the patient-reported MG Activities of Daily Living scale (MG-ADL) and the 15-item MG Quality of Life questionnaire (MG-QoL15), and the physician-reported Quantitative MG score (QMG), the MG manual muscle test (MG‐MMT), and the MG Composite scale (MGC).
“However, data on the performance of these outcome measures in the setting of rapidly efficacious therapies, such as [plasma exchange], are sparse,” the researchers wrote, adding that these data “could be invaluable in planning clinical trials of rapidly efficacious therapies for MG.”
Researchers evaluated the performance of MG‐ADL, MG‐QoL15, MG‐MMT, and MGC in MG patients who received a plasma exchange for an MG exacerbation at Duke University Medical Center and the University of North Carolina at Chapel Hill Hospital.
This analysis was part of the secondary goals of an open-label trial evaluating plasma exchange in 10 people (six men and four women) with MG and autoantibodies against AChR. The study met its primary goal, showing that plasma exchange effectively reduced the levels of immune-related molecules including AChR autoantibodies.
Researchers have now assessed changes in MG-specific clinical outcome measures between the beginning of the study and two weeks after plasma exchange (a time-point previously used in studies of this type of treatment), as well as potential associations between changes in outcome measures and levels of immune-related molecules (the study’s secondary goals).
In this analysis, changes of three or more points in MG‐ADL, MG‐QoL, MG‐MMT, and MGC scores were considered clinically significant.
Participants’ median age was 72.9 years, and 90% were Caucasian and had moderate disease severity at the time of enrollment. They received five to six plasma exchange sessions (one plasma volume per session) every other day, in accordance with institutional practices.
Two weeks after plasma exchange, patients’ scores on the MG‐ADL, MG‐QoL15, MG‐MMT, and MGC showed statistically significant changes and clinically significant improvements.
Patients’ scores continued to improve across all measures, with the strongest improvements occurring at six weeks after treatment for patient-reported MG‐ADL and MG‐QoL15 and at 12 weeks post-treatment for physician-reported MG‐MMT and MGC.
“Some of the continued reduction in patient‐reported outcomes after the completion of [plasma exchange] treatment may reflect a delay in returning to a more normal lifestyle after intensive therapy and in some cases, hospitalization,” the team wrote, adding that this factor should be considered in future clinical trials using these outcome measures.
Results also showed strong associations between scores on the MG‐ADL and MGC, MG‐QoL15 and MGC, and MG‐MMT and MGC. Researchers noted the data suggests that physician-reported MGC could be used to establish the “yet undetermined clinically meaningful improvement in the MG‐QoL15.”
The team found no association between plasma exchange-associated changes in outcome measures and levels of immune-related molecules, which they noted was consistent with what was reported in previous studies.
“Such weak correlation between [levels of immune-related molecules] and clinical response indicates that validated, MG‐specific clinical outcome measures should continue to be the primary means of assessing response to existing and novel rapidly efficacious therapies in clinical trials for the foreseeable future,” they wrote.
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