Unusual Sequential Development of Multiple Sclerosis, Thymoma, Myasthenia, and Lymphoma in the Same Patient.

No case has yet been described in which a patient developed multiple sclerosis (MS) followed by thymoma, myasthenia gravis (MG), and T-cell lymphoma. The patient is a 47-year-old woman who developed relapsing-remitting MS at the age of 31 and was treated with interferon-beta (IFN-β) for over seven years. She was then diagnosed with thymoma, which was treated with chemotherapy and surgery. One year later, she was diagnosed with MG, which was treated with steroids, pyridostigmine, and intravenous immunoglobulins. Due to an MS relapse at the age of 40, ocrelizumab was administered for 2.5 years, after which she developed T-cell lymphoma. As the lymphoma had responded only partially to chemotherapy, an autologous stem cell transplantation was performed. It remains unclear whether there was a causal link between the immunosuppressive MS treatment and the thymoma or lymphoma, whether these developed due to underlying immune dysregulation, individual predisposition, or the cumulative effect of prior oncological therapies, or whether this was merely a chance co-occurrence of rare diseases. The case shows that a single patient may sequentially develop MS, MG, thymoma, and T-cell lymphoma. Fundamental and comprehensive clinical studies are required to elucidate the underlying pathophysiology and to confirm or refute a possible causal link.