How is MS Diagnosed? When faced with a patient whose symptoms, neurological examination, and medical history suggest MS, physicians use a variety of tools to rule out other possible disorders and perform a series of laboratory tests which, if positive, confirm the diagnosis. Imaging technologies such as MRI-often used in conjunction with the contrast agent gadolinium, which helps distinguish new plaques from old on MRI (see section on "What is the Course of MS?")-can help locate central nervous system lesions resulting from myelin loss. However, since these lesions can also occur in several other neurological disorders, they are not absolute evidence of MS. Magnetic resonance spectroscopy (MRS) is a new tool being used to investigate MS. Unlike MRI, which provides an anatomical picture of lesions, MRS yields information about the biochemistry of the brain in MS. Evoked potential tests, which measure the speed of the brain's response to visual, auditory, and sensory stimuli, can sometimes detect lesions the scanners miss. Like imaging technologies, evoked potentials are helpful but not conclusive because they cannot identify the cause of lesions. The physician may also study the patient's cerebrospinal fluid (the colorless liquid that circulates through the brain and spinal cord) for cellular and chemical abnormalities often associated with MS. These abnormalities include increased numbers of white blood cells and higher-than-average amounts of protein, especially myelin basic protein and an antibody called immunoglobulin G. Physicians can use several different laboratory techniques to separate and graph the various proteins in MS patients' cerebrospinal fluid. This process often identifies the presence of a characteristic pattern called oligoclonal bands. Because there is no single test that unequivocally detects MS, it is often difficult for the physician to differentiate between an MS attack and symptoms that can follow a viral infection or even an immunization. Many doctors will tell their patients they have "possible MS." If, as time goes by, the patient's symptoms show the characteristic relapsing-remitting pattern, or continue in a chronic and progressive fashion, and if laboratory tests rule out other likely causes, or specific tests become positive, the diagnosis may eventually be changed to "probable MS." A number of other diseases may produce symptoms similar to those seen in MS. Other conditions with an intermittent course and MS-like lesions of the brain's white matter include polyarteritis, lupus erythematosus, syringomyelia, tropical spastic paraparesis, some cancers, and certain tumors that compress the brainstem or spinal cord. Progressive multifocal leukoencephalopathy can mimic the acute stage of an MS attack. The physician will also need to rule out stroke, neurosyphilis, spinocerebellar ataxias, pernicious anemia, diabetes, Sjogren's disease, and vitamin B12 deficiency. Acute transverse myelitis may signal the first attack of MS, or it may indicate other problems such as infection with the Epstein-Barr or herpes simplex B viruses. Recent reports suggest that the neurological problems associated with Lyme disease may present a clinical picture much like MS. Investigators are continuing their search for a definitive test for MS. Until one is developed, however, evidence of both multiple attacks and central nervous system lesions must be found-a process that can take months or even years-before a physician can make a definitive diagnosis of MS.