Thymoma-Associated Systemic Lupus Erythematosus and Myasthenia Gravis

Summary: Background: The thymus plays a crucial role in nurturing cell-mediated immunity and ensuring self-tolerance. Thymoma, a rare tumor originating from thymic epithelial cells, has the potential to disrupt this process by promoting the emergence of autoreactive lymphocytes, thereby increasing the risk of autoimmune disorders. The association between thymoma and autoimmune diseases, such as myasthenia gravis is well-established. Conversely, the link between thymoma and systemic lupus erythematosus (SLE) is less frequently observed. In this report, we present the case of a young adult woman diagnosed with both SLE and myasthenia gravis, who was also found to have a thymoma. Case Presentation: A 32-year-old woman with SLE was admitted to the hospital presenting with a headache, blurred vision in her right eye, generalized weakness, and dysphagia. The headache had begun three days prior to admission, localized to the right retro-orbital area and accompanied by blurred vision. She had been experiencing dysphagia and weakness for the past year, with symptoms intensifying in the three weeks leading up to admission. Her SLE had been diagnosed a year earlier, initially presenting with polyarthritis, positive antinuclear antibody (ANA; 1:640 homogenous pattern), low levels of C3 and C4, and elevated anti-dsDNA and anti-Ro antibodies. Treatment included prednisone 10 mg daily, hydroxychloroquine 200 mg daily, and mycophenolate mofetil 500 mg twice daily. On physical examination, right palpebral ptosis and proximal muscle weakness in the upper extremities were noted. No rash, alopecia, mucosal ulcers, or joint tenderness or swelling were observed. Laboratory tests revealed a positive ANA (1:160, homogeneous pattern), elevated dsDNA antibodies, low C3 and C4 levels, and positive anti-Mi-2 and anti-acetylcholine receptor (AChR) antibodies. All three types of AChR antibodies (blocking, modulating, and binding) were detected. Serum levels of creatine phosphokinase and aldolase were within normal limits. A chest computed tomography (CT) scan revealed an anterior mediastinal mass with left pleural and left brachial and cephalic veins invasion (Figure 1). A CT-guided biopsy of the mass showed a thymoma most consistent with World Health Organization type AB. Immunohistochemistry was positive for BCL2, CD3, CD5, CK19, CK-Pankeratin, Ki-67, p40, p63, and PAX-8. She was diagnosed with myasthenia gravis and started on intravenous immunoglobulin for five days, pyridostigmine 30 mg three times a day, and prednisone 40 mg daily. After improvement of symptoms, she was discharged with neurology, hematology-oncology, and cardiothoracic surgery follow-up. Discussion: Thymomas have the potential to disturb the regular process of T-cell maturation, potentially enabling autoreactive lymphocytes to evade elimination, thereby contributing to the development of autoimmune disorders. Consequently, this disturbance can lead to the onset of various autoimmune disorders, such as myasthenia gravis, autoimmune cytopenias, inflammatory myositis, Hashimoto’s thyroiditis, SLE, rheumatoid arthritis, systemic sclerosis, Sjogren’s syndrome, and sarcoidosis. Among these autoimmune conditions, myasthenia gravis exhibits the highest frequency of association, reported in up to 30-50% of patients. In contrast, SLE shows a less common association, linked to approximately 1.5-2% of patients. While our patient did not present clinical symptoms consistent with dermatomyositis, anti-Mi2 antibodies were detected. To the best of our knowledge, although inflammatory myositis has been described alongside myasthenia gravis, the co-occurrence of thymoma and anti-Mi2 antibodies has not been previously reported. Conclusions: We present a case of thymoma-associated paraneoplastic syndrome manifesting as both SLE and myasthenia gravis. Clinicians should be vigilant, recognizing that patients displaying atypical clinical presentations or overlapping features of autoimmune disorders may warrant consideration of an underlying condition, potentially including malignancy.