The described symptoms are not typical of MS but it is a notoriousely difficult diagnosis to rule out on purely clinical grounds. Because no single test is totally reliable in identifying MS, and a variety of conditions can mimic the disease , diagnosis depends on clinical features supplemented by the findings of certain studies. Magnetic resonance imaging, MRI, has become one of the most important diagnostic tools for MS. Magnetic resonance imaging with gadolinium contrast, especially during or following a first attack, can be helpful in providing evidence of lesions in other parts of the brain and spinal cord. A second magnetic resonance scan may be useful at least three months after the initial attack to identify new lesions and provide evidence of dissemination over time. It is critical to exclude other diseases that can mimic multiple sclerosis, including vascular disease, spinal cord compression, vitamin B12 deficiency, central nervous system infection (e.g., Lyme disease, syphilis), and other inflammatory conditions (e.g., sarcoidosis, systemic lupus erythematosus, Sjögren' s syndrome). MRI is useful in all these regards.