Myasthenia gravis (MG) is an antibody-mediated neuromuscular disease affecting the neuromuscular junction. In most cases, autoantibodies can be detected in the sera of MG patients, thus aiding in diagnosis and allowing for early screening. However, there is a small proportion of patients who have no detectable auto-antibodies, a condition termed “seronegative MG” (SnMG). Several factors contribute to this, including laboratory test inaccuracies, decreased antibody production, immunosuppressive therapy, immunodeficiencies, antigen depletion, and immune-senescence. The diagnosis of SnMG is more challenging and is based on clinical features and neurophysiological tests. The early identification of these patients is needed in order to ensure early treatment and prevent complications. This narrative review aims to examine the latest updates on SnMG, defining the clinical characteristics of affected patients, diagnostic methods, management, and therapeutic scenarios.

Background: Myasthenia gravis (MG) is an autoimmune disease characterized by fluctuating muscle weakness due to autoantibodies targeting neuromuscular junction proteins. Mycophenolate mofetil (MMF), an immunosuppressive therapy, has shown potential for managing MG with fewer side effects compared to other treatments. This study aims to evaluate the effectiveness and safety of MMF in MG patients in a real-life multicenter setting. Methods: A retrospective cohort study was conducted on generalized MG patients, refractory to azathioprine (AZA) and treated with MMF alone or with steroids, at three Italian centers from January 2011 to February 2024. Patients were assessed using the Myasthenia Gravis Foundation of America (MGFA) classification, MG composite score (MGCS), and MG activity of daily living (MGADL) scores at baseline, 6, 12, 18, and 24 months. Statistical analyses included the Spearman correlation, the Friedman test, and ANOVA. Results: Thirty-two patients were enrolled (13 males, mean age 66.5 ± 11.5 years). Significant improvements in MGADL and MGCS scores were observed at 6 and 12 months (p < 0.001), with continued improvement over 24 months. Side effects were reported in 12% of patients. MMF showed a faster onset of symptom control compared to azathioprine, with a significant improvement noted within 6 months. Conclusions: A recent study found that MMF and AZA were equally effective in improving patients’ quality of life, but because AZA had more serious adverse events than MMF, lower doses of AZA were therefore recommended to reduce the adverse events while maintaining efficacy. Conversely, results showed that MMF is effective and well-tolerated in the long-term management of MG, providing faster symptom control and a favorable safety profile. Future prospective studies with larger cohorts are needed to confirm these findings and explore sex differences in response to MMF treatment.