Anti-musk antibody myasthenia gravis: Clinical findings and long term follow up

Abstract

Myasthenia gravis (MG) is adisorder neuro-muscular junction where 50-85% patients have acetylcholine receptor antibody (AChR-Ab). About 30-40% sero-negative patients have antibodies to muscle-specific tyrosine kinase (MuSK). This disorder represents a distinct subset of MG where clinical features and treatment options are different. We retrospectively analysed MuSK-MG patients seen at our center in last 4 years. From 2015 to 2019, there were 6 MuSK-MG patients. Eighty-three percent were female, with disease onset in the fourth to fifth decade. Oculobulbar symptoms were present at onset in 83%. Eventually ocular involvement was seen in 83%, bulbar in 83% and limbs weakness in 83%. Fifty percent patients had myasthenic crisis. No patient had antibodies to AchR and of those tested, CT scan of thorax did not show any thymic tumour. No patients responded to pyridostigmine. Sixty six percent patients had moderate to good response to steroids. Sixty six percent patients were treated with plasma exchange (PLEX) which produced improvement while none was treated with intravenous immunoglobulin. Immunosupression with azathioprine (50%), mycophenolate (16%) and rituximab (50%) was used during the course of illness. All patients achieved good remission over a median follow up of 2 years. MuSK-MG has a marked female predominance with frequent oculobulbar weakness and crises. Pyridostigmine does not help to relieve symptoms and PLEx shows better results compared to steroids. Most patients need immunosuppression and remission can be achieved with it.