Myasthenia gravis associated with anti-MuSK antibodies developed after SARS-CoV-2 infection

Introduction: Since the onset of the novel coronavirus pandemic, several neurological complications secondary to SARS-CoV-2 infection have been reported, affecting central nervous system, peripheral nervous system and neuromuscular junction. Case report: We present the case of a 77-year-old man who developed bulbar myasthenia gravis (MG) eight weeks after SARS-CoV-2 infection. The search for serum antibodies against the acetylcholine receptor and the muscle-specific tyrosine kinase (MuSK), performed by radioimmunoassay (RIA), and the search of low-density lipoprotein receptor-related protein 4 antibodies, performed by immunohistochemistry, resulted negative, while anti-MuSK antibodies were detected by cell-based assay (CBA). The patient was treated with pyridostigmine (60 mg four times a day) with unsatisfactory clinical response, followed by immunosuppressive therapy (azathioprine 1.5 mg/kg/day) with improvement of MG symptoms after two months of treatment. Discussion: Several viral diseases have been described as associated with the onset of MG, although the underlying mechanisms are not yet fully understood. Similarly, a growing number of scientific reports suggest a correlation between SARS-CoV-2 infection and autoimmune diseases. The interest of our case lies in the timing of the MG onset (after 2 months from infection), together with the unusual late onset of anti-MuSK MG. These elements suggest that coronavirus infection may act as a trigger of the disease. We confirm the importance of CBA in the serological diagnosis of RIA-negative MG.