Both disorders had been controlled for around 15 years by oral prednisolone and a cholinesterase inhibitor following surgical removal of invasive thymoma and radiotherapy, but muscular weakness due to myalgia and an increase in serum levels of myogenic enzymes, mainly ascribable to the recurrence of PM, reappeared immediately after cessation of these drugs, which was done because the patient had multiple bone fractures and severe osteoporosis due to the long-term corticosteroid therapy.