Myasthenia

The purpose of the study is to evaluate if there is a specific association between the presence of anti Rach antibodies in the CSF and the presence of a cogntive disorder in myasthenic patients. Moreover the investigator wants to study if there is a link between the presence of Anti RACH antibodies in myasthenia and Alzheimers's disease. For that, the investigator will recruit myasthenic patient with cognitive disorder that has undergo a diagnostic process including lombar punction for memory trouble in Nice memory center as well as Alzheimer's patient having go through the same process. The study will consist in one additionnal blood draw. Anti RACH antibodies will be analyzed in historical CSF stored in biocollection and serum collected for the study. LCS of healthy control will also be analyzed.

The goal of this observational study is to learn about the experiences of people living with Myasthenia Gravis (MG) in the United States. The main questions it aims to answer are: * How and when are people with MG diagnosed? * What are the most common symptoms associated with MG? * What treatments are being used to treat MG? * What are the impacts of MG on activities of daily living, employment and quality of life? * What are the experiences with exacerbation, hospitalization and healthcare access for people with MG? Participants will answer a survey to enroll in the study, and be invited to fill out an update survey twice a year.