: This study aimed to present a case of a clinically isolated syndrome (CIS) with a reported tumefactive demyelinating lesion (TDLs) in the cord. The patient was a 25-year-old woman who referred to MS Clinic complaining of walking impairment and a blurred vision in the right eye. In the magnetic resonance imaging (MRI) of the brain, there were several periventricular plaques, a significant portion of which had enhanced, but none of the lesions was tumefactive. In the cervical MRI, however, several tumefactive plaques appeared with a clear enhancement and expansion, which was central-based in the axial view. Concerning the involvement of the cervical cord, further examinations were conducted of anti-aquaporin and anti-myelin oligodendrocyte glycoprotein (MOG) antibodies, which were negative. The patient was treated with 1g methylprednisolone daily injection for five days; her symptoms recovered completely. Then, due to the extent of the involvement, rituximab was prescribed for her. Unlike the TDLs of the brain, little attention has been paid to these lesions in the cord. Here, firstly a case of CIS with a tumefactive lesion reported in the cord is investigated, and then, by examining similar cases, we try to find a definition for cord TDLs.