Myositis associated to COVID-19 mimics an acute exacerbation in myasthenia gravis patient

Coronavirus disease 2019 (COVID-19) is an acute infection of the respiratory tract spread into a global pandemic. Emerging case reports have described neurological manifestations in patients with COVID-19 infection including headache, seizure, Guillian-Barrè syndrome and encephalitis. Here we report a case of a patient affected by myasthenia gravis (MG) who developed a severe myositis post COVID-19. A 45 years-old woman affected by MG since she was 30, presented to our Neurological Department reporting severe weakness prevalent in upper limbs, diffuse myalgia, dysphagia and dyspnea started two months after COVID-19 infection. We administered intravenous immunoglobulin (IVIG) in suspecting of MG aggravation, however without clinical improvement. A full blood panel showed elevated Creatine-Phosphokinase (CPK) and Lactate-dehydrogenase (LDH) levels. Autoimmune screening revealed low level of complement C3, positive antibodies anti-Nuclear (ANA) and anti-Phospolipide (aPL), included anti-Cardiolipin (aCL) and anti-β2-glycoprotein I (aβ2GPI). Electromyographic (EMG) examination showed: diffuse spontaneous activity with positive sharp wave (PSW), fibrillation potential, small and short motor unit action potentials (MUAPs) in quantitative analysis, suggesting acute myopathic pattern. We performed therapy with intravenous Methylprednisolone for five days with full clinical recovery. One month later, EMG features were significantly improved. Viral infection is a well-known cause of myositis described also in patients with COVID-19, probably due to the expression of ACE-2 on the muscle cells. To our knowledge, this is the first case in literature of myositis associated to COVID-19 infection in MG patients. We want to underline how myositis symptoms could mimic an acute exacerbation of MG leading to harmful misdiagnosis.