Thymectomy May be Effective Only For Some Forms of Myasthenia Gravis
Although randomized trials demonstrate that treatment with thymectomy has benefits for patients with nonthymomatous antiacetylcholine receptor (AChR) antibody positive generalized myasthenia gravis (MG), uncontrolled observational studies has suggested that it may not have benefit for those with ant-muscle-specific kinase (MuSK) MG. This is now supported with data from a multicenter, retrospective blinded review of the use of rituximab in anti-MuSK MG. This data was presented at the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) 34thAnnual Meeting in Washington DC Oct 10-12.
Patients with MuSK MG treated with thymectomy (n = 26) and nonthymectomy, including treatment with rituximab were followed for 3 years. Of those who had thymectomy, 9 of 26 (35%) had favorable outcomes; 16 of 29 patients given nonthymectomy treatments had favorable outcomes. The difference between the groups was not statistically significant (P = .017).
The primary outcome was the Myasthenia Gravis Foundation of America (MGFA) Post-Intervention Status (PIS). A score of minimal manifestations on the MGFA PIS was defined as a favorable outcome. The blinded case review also evaluated other immunosuppresent medications, intravenous immunoglobulin (IVIG) or plasmapheresis (PLES) treatment, MG Status and Treatment Intensity (MGSTI) score, and prednisone dose.
Of those treated with thymectomy, 69% were taking prednisone (median dose 10 mg/day) versus 41% of patients treated with nonthymectomy regimens (median dose 0 mg/day, P = .04). After controlling for IVIG/PLEX level, baseline prednisone, and rituximab, thymectomy was not associated with greater likelihood of favorable clinical outcome.
Although this study shows no evidence for the benefits of thymectomy in patients with MuSK MG, the broad confidence intervals also cannot exclude therapeutic effect (OR: 0.43, 95% CI: 0.13-1.48, P = 0.18).