Case report: Efgartigimod combined with intravenous methylprednisolone in a case of co-occurrence of unexplained myasthenia gravis, inflammatory myopathy, and fulminant myocarditis.

The co-occurrence of myasthenia gravis (MG), inflammatory myopathy (IM), and fulminant myocarditis (FM) has rarely been reported. The few previous articles were mostly case reports or small sample data analysis, and the etiology was mostly attributed to thymoma and/or the application of immune checkpoint inhibitors (ICIs). We report a 74-year-old woman with an acute onset of general weakness, chest tightness, shortness of breath, dysarthria, masticatory weakness and dysphagia, without myalgia or rash. Acetylcholine receptor antibody was positive. Serum creatine kinase, transaminase, and myoglobin were higher than normal. A variety of autoimmune antibodies including anti-Ro-52, JO-1, nRNP and dsDNA antibodies were positive. Chest CT showed no thymoma, bronchiectasis with infection in both lungs. Some of them showed interstitial changes. Electromyography repetitive nerve stimulation of the bilateral deltoid muscle demonstrated a decremental response at low frequencies without an incremental response at high frequencies. Needle electromyography revealed spontaneous potentials. Echocardiography showed that left ventricular wall motion was generally reduced, left ventricular systolic function was reduced, and cardiac function was EF18%. Muscle biopsy suggested myogenic injury. The patient was diagnosed with MG-IM-FM coexisting without thymoma and without ICIs. After treatment with Efgartigimod combined with intravenous methylprednisolone, the symptoms were relieved, serum creatine kinase, myoglobin and other laboratory indicators and cardiac function returned to normal. MG-IM-FM is a complex disease with rapid onset, rapid progression and critical condition. Clinicians should be on high alert and early intervention is the key to improve the prognosis. The immune mechanism of its occurrence is still unclear and needs to be further studied. Traditional glucocorticoid is still the first-line drug, but the new targeted drug Efgartigimod has less adverse reactions and faster onset of action, which may become a good choice, but needs to be verified by a larger sample.