Anti-Kv1.4 Antibody-positive Nivolumab-induced Myasthenia Gravis and Myositis Presenting with Bilateral Ptosis and Demonstrating Different Pathophysiologies.

Nivolumab blocks inhibitors of T-cell activation and restores antitumor immunity but promotes T-cell activity in host tissues by blocking inhibition of the T-cell function, resulting in immune-related adverse effects. We herein report an 80-year-old man presenting with nivolumab-related myasthenia gravis with anti-muscular voltage-gated potassium channel-complex (Kv1.4) antibodies. On day 29 after nivolumab administration, he simultaneously developed rapidly progressing right ptosis and left facial paralysis. Nivolumab administration was discontinued. He subsequently presented with bulbar paralysis, dyspnea, and muscle weakness and received intravenous immunoglobulin, methylprednisolone, and plasma exchange. The severity of nivolumab-related myasthenia gravis with anti-Kv1.4 antibodies presented with diverse clinical findings.

Magnetic resonance imaging findings of the lower limb muscles in anti-mitochondrial M2 antibody-positive myositis.

Anti-mitochondrial M2 antibody (AMA-M2)-positive myositis is an idiopathic inflammatory myopathy (IIM). Of all patients with myositis, 2.5-19.5% have AMA-M2 antibodies. However, the detailed distribution of muscles affected in AMA-positive myositis is unknown. Therefore, we examined lower muscle magnetic resonance imaging (MRI) findings of patients with AMA-positive myositis. Among the 63 patients with IIM at our institute, 5 (7.9%) were positive for AMA-M2 antibodies. However, one was also positive for anti-Jo1 antibodies; therefore, four patients were finally participated in this study. All patients had high-intensity MRI signals in the proximal muscles, including the gluteus maximus and iliopsoas muscles, and in the thigh muscles, including the vastus lateralis, vastus medialis, adductor magnus, and semimembranosus muscles. Lower leg muscles were relatively spared. Fascial edema was observed in all patients and was also present in the lower leg muscles. Subcutaneous edema was observed, particularly in the proximal portion of the lower limbs. In AMA-positive myositis, proximal muscles, including the gluteus maximus, vastus lateralis, adductor magnus, and the semimembranosus, were markedly affected, while the lower leg muscles were relatively preserved. Additionally, fascial edema was evident even in lower leg muscles. Therefore, muscle MRI can be a useful diagnostic aid for AMA-positive myositis.