Multiple sclerosis (MS) is a common demyelinating disease of the central nervous system in which an abnormal immune system response results in damage to the myelin sheaths surrounding nerves. The etiology of MS remains elusive, although it has been suggested to be influenced by both genetic and environmental factors. Here, we report two exceptional cases of patients affected by both MS and Thomsen's myotonia. Electromyography and MRI scans confirmed the presence of both diseases in the referred cases. Although the mechanisms underlying the co-occurrence of MS and Thomsen's disease are unclear, we have endeavored to offer plausible explanations for it.