Occasional detection of thymic epithelial tumor 4 years after diagnosis of adult onset Still disease A challenging case report and immuno-oncological considerations coming from pertinent literature review

Background: Thymoma is a T cell neoplasm arising from the thymic epithelium that due to its immunological role, frequently undercover derangements of immunity such a tumors and autoimmune diseases. Methods:Herein, we report, to the best of our knowledge, the first description of an association between thymoma and adult onset Still disease (AOSD) in a 47-year-old man. The first one was occasionally detected 4 years later the diagnosis of AOSD, and surgically removed via right lateral thoracotomy. Histology confirmed an encapsulated thymic tumor (type AB sec. WHO-classification). Results: The AOSD was particularly resistant to the therapy, requiring a combination of immunosuppressant followed by anti-IL1R, that was the only steroids-sparing treatment capable to induce and maintain the remission. The differential diagnosis was particularly challenging because of the severe myasthenic-like symptoms that, with normal laboratory tests, were initially misinterpreted as fibromyalgia. The pathogenic link of this association could be a thymus escape of autoreactive T lymphocytes causing autoimmunity. Conclusion: Clinicians should be always include the possibility of a thymoma in the differential diagnosis of an unusual new onset of weakness and normal laboratories data, in particular once autoimmune disease is present in the medical history.