Initial deterioration and intravenous methylprednisolone therapy in patients with myasthenia gravis.

•Intravenous methylprednisolone (IVMP) is one of the main therapies for MG patients.•We studied initial deterioration (id) for high-dose IVMP in mainly mild MG patients.•The mode of onset and duration for id were day 4 and 3 days from initial day of IVMP.•IVMP can be repeated weekly after initial deterioration in most patients.•Related factors were MGFA classification and thymectomy before IVMP.