Objective: To describe what we believe is the first reported case of MuSK Myasthenia Gravis (MG) after COVID-19.
Case Report: A 24-year-old previously healthy woman of Pakistani origin presented to the emergency department in June 2020 with a flu-like illness consistent with COVID-19. She was discharged without a SARS-CoV-2 swab test. She self-isolated at home and recovered completely.
Four weeks later, she developed diplopia, slurred speech, dysphagia, and global limb weakness. Examination revealed bilateral fatigable ptosis, complex ophthalmoplegia, symmetrical lower motor neuron facial weakness, and dysarthria. She had weakness and fatigability in all 4 limbs. Neck flexion and extension were also weak. Reflexes were brisk and symmetrical throughout. Her FVC was 0.97 L, so she was transferred to intensive care for monitoring without ventilator support.
Bloods for CK, TFTs, ANA, ANCA and antiganglioside antibodies were normal/negative. SARS-CoV-2 antibodies were detected. MRI brain and spine were unremarkable. CSF constituemts were normal. Single-fibre electromyography of the left orbicularis oculi was abnormal. Repetitive nerve stimulation of the left abductor digiti minimi muscle showed abnormal decrementing responses. Computed tomography of the chest revealed no thymoma.
AChR antibodies were negative but MuSK antibodies were positive, confirming the diagnosis of generalised MuSK-Myasthenia Gravis
We administered intravenous immunoglobulin, pyridostigmine, and prednisolone which led to symptom improvement. However, the effect of intravenous immunoglobulin was relatively short-lived. She developed side effects with higher doses of pyridostigmine, so we reduced the dose and added salbutamol. She is now 20 weeks from symptom onset and is receiving 50 mg of prednisolone every other day. She has mild to moderate dysarthria and mild limb weakness. If her condition relapses as her steroids are reduced, we will consider treatment with rituximab.
Discussion: Other authors have reported that MuSK-MG may develop after viral infection (1), Although our findings demonstrate a temporal association between COVID-19 infection and MuSK-MG, we recognise that we cannot definitively conclude causality. Nevertheless, we believe that this report of MuSK-MG associated with COVID-19, along with reports of AChR-MG associated with COVID-19 (2), provide clues to possible mechanisms for the association. For example, cross-reactivation of SARS-CoV-2 antibodies with both AChR and MuSK proteins is highly unlikely given their molecular differences; therefore, the development of myasthenia gravis after COVID-19 more likely represents a breakdown in self-tolerance mechanisms than cross-reactivation. Long-term follow-up will determine whether this case of MuSK-MG is an acute, monophasic, post-infectious phenomenon or a chronic autoimmune disorder requiring long-term immunosuppressive treatment.