Science News: Rate of Change in Acetylcholine Receptor Antibody Levels Predicts Myasthenia Gravis Outcome

Submitted by: Francisco Gomez, MD
Edited by: Pritikanta Paul, MD

Kojima Y, Uzawa A, Ozawa Y, et al. Rate of change in acetylcholine receptor antibody levels predicts myasthenia gravis outcome. J Neurol Neurosurg Psychiatry. 2021;92(9):963-968. doi:10.1136/jnnp-2020-325511

Summary: Up to 80% of myasthenia gravis (MG) patients are seropositive for anti-acetylcholine receptor antibodies (AChR-Ab) and these antibodies are routinely checked as diagnostic markers in clinical practice. However, their use in prognosis is thought to be limited.
 
This is a single center, retrospective chart review study wherein the authors investigated the correlation between change in AChR-Ab levels after therapy and treatment outcome. They introduced measuring antibody level reduction rate [(AChR-Ab level pretreatment-ACh level post-treatment)/AChR-Ab level pretreatment/days] between treatment initiation and remeasurement of AChR-Ab at 100 days following initiation of treatment. They included a total of 53 patients diagnosed with MG, who received treatment with prednisolone and/or tacrolimus for maintenance therapy, of whom 5 underwent treatment with IVIG or plasmapheresis during the study period. The primary outcome was described as achieving minimal manifestation (MM) or better status at 1 year following immunosuppressive treatment. The authors calculated the cutoff for antibody reduction rate (RR AChR-Ab) as 0.64%/day.  They found more patients with higher reduction rate achieved MM or better status at 1 year (90% vs 65% p=0.03) compared to myasthenics with lower reduction rate. They concluded Ab remeasurement within 100 days of therapy initiation may be a useful tool for prognosis and possibly measuring treatment response.

Comments: AChR-Ab testing is already in widespread use as a diagnostic tool. Expanding the utility of this test in prognostication and guiding treatment could aid clinicians in optimizing therapy for individual patients. It can be helpful but only if the antibody levels are calculated carefully, employing serial serum dilutions. Most commercial and hospital laboratories use single concentrations, designed for sensitivity and specificity, rather than interpretation of treatment responses. Clinicians need to be careful when ordering test for treatment monitoring.