Thymoma and multiple sclerosis: coincidence or causal association?

Case Presentation A 59-year-old woman presented acutely with paroxysmal sensory symptoms on the right side of her body, sparing the face, presumably due to a cervical spinal cord lesion. She denied any previous episodes consistent with demyelinating disease. MRI of the brain showed juxtacortical, periventricular, and infratentorial lesions suggestive of MS (none with contrast enhancement), whereas MRI of the cervical and dorsal spinal cord was unremarkable; CSF analysis showed exclusive oligoclonal bands, and an extensive workup ruled out other causes, therefore she fulfilled the criteria for relapsing-remitting MS. A 3-day course of intravenous methylprednisolone led to partial recovery and she was then started on dimethyl fumarate. As part of the diagnostic workup, she had done a CT scan of the thorax, which revealed a 4.6 x 2.0 cm mass in the anterior mediastinum, compatible with thymoma. Following video-assisted thoracoscopic thymectomy, pathology confirmed a mixed B1/B2, Massaoka IIB thymoma, and adjuvant radiotherapy was adminstered. At 6 months after the initial presentation, there had been no further relapses or MRI activity and her EDSS remained stable at 1.5. Discussion In this case, the onset of MS at the sixth decade of life (which is quite uncommon) and in close temporal association with the diagnosis of thymoma (a frequent cause of neurological paraneoplastic syndromes) raise the possibility of a causal link between these conditions. Additional pathology studies are underway to examine whether this patient’s thymoma expressed the myelin basic protein or other myelin antigens, which could support the hypothetical link with MS in this case. Final Comments While thymomas have been associated with myasthenia gravis, neuromyelits optica and other autoimmune conditions, its co-occurrence with multiple sclerosis (MS) is much rarer, with fewer than 10 cases reported so far. We herein report a new case.