Clinical Characteristics of Double SeroPositive Myasthenia Gravis

Objective This study aims to delineate the clinical phenotype of DSP-MG and assess the histopathological correlation with thymoma. Background Double SeroPositive Myasthenia Gravis (DSP-MG), a rare autoimmune disease that affects neuromuscular transmission, is characterized by antibodies against both AChR and MuSK receptors. This is the second study to be conducted in the world which attempts to define the clinical phenotype of DSP-MG patients. Design/Methods This is a retrospective case series conducted at a tertiary care hospital in South India conducted between February 2018 and October 2021. All patients who were diagnosed with DSP-MG based on typical clinical presentation and positive titres of both Anti- AChR and Anti-MuSK antibodies were included in the study. Results This study consisted of 13 DSP-MG patients (7 Females, Mean age- 60.77 +/-14.24). The presentation was generalized in 9 patients, bulbar in 3 and ocular in 1 patient. Severity of the disease was assessed using the Modified Osserman System wherein 5 patients were Grade 4, 4 patients in grade 3, 3 patients in grade 2 while 1 patient was grade 1. The muscle groups affected first were the limbs (n = 6), ocular (n = 5), bulbar (n = 3) and respiratory (n = 1). MDCT done in 11 patients showed thymoma in five and thymic hyperplasia in 1. Four patients underwent thymectomy whose histopathology showed Type A, B2 (n = 2) and AB thymomas. Four patients had associated thyroid dysfunction and 3 patients were found to have developed MG post stroke. All 13 patients improved with Anticholinesterases, 9 patients were administered immunosuppressants, 3 patients were given IVIg and a single patient underwent plasmapheresis. Conclusions Our study shows that DSP MG is more similar to the clinical phenotype of AChR-MG, rather than MuSK-MG that has been previously defined in literature.