Long-term efficacy and safety of tacrolimus in anti-MuSK antibody-positive myasthenia gravis: a retrospective single-center cohort study.

Objective: To evaluate the long-term efficacy and safety of tacrolimus in patients with muscle-specific kinase antibody-positive myasthenia gravis (MuSK-MG).

Methods: We performed a retrospective, single-center, and cross-sectional study analyzing medical records of 18 MuSK-MG patients treated with tacrolimus for more than 1 year. The efficacy and safety of tacrolimus were evaluated by modified Osserman scale, Myasthenia Gravis Foundation of America post-intervention status, prednisone dosage, quantitative MG (QMG) scores, MG-activity of daily living (MG-ADL) scores, anti-MuSK antibody titers, blood routine, and serum biochemicals.

Results: After 4 weeks of tacrolimus treatment, there was a significant improvement in prednisone dose, QMG, and MG-ADL scores, which continued to improve over 1 year. In addition, clinical grade of modified Osserman scale was improved in all patients, 16 (88.9%) of whom were asymptomatic at the last visit. More importantly, the mean titers of anti-MuSK antibody were significantly decreased from 0.777 ± 0.381 to 0.283 ± 0.178 nmol/L after a median of 1.4 years of tacrolimus treatment in 9 patients with MuSK-MG (P = 0.015). All patients achieved minimal manifestations status (MMS) after tacrolimus treatment (range, 4-32 weeks). Subsequently, seven patients (38.9%) underwent a taper of tacrolimus dosage. However, four patients (57.1%) experienced an exacerbation. Adverse events occurred in 2 patients (11.1%), all of which were mild and resolved after the tacrolimus dose was adjusted or discontinued.

Conclusion: Our results suggest that tacrolimus may be an effective and safe steroid-sparing treatment for patients with MuSK-MG. However, tacrolimus should be carefully tapered to avoid disease exacerbation.