UNIVERSITY OF CALIFORNIA - SAN FRANCISCO MEDICAL CENTER: CLICK TO READ MORE"The diagnosis of MS is based upon a clinical evaluation including documentation of "symptoms" and "signs" of the disease. Symptoms are the experiences of the patient. Examples of symptoms include double vision, tingly sensations, or difficulty controlling the bladder. Signs are abnormalities found on neurological examination and must be evident to the neurologist. Examples of signs include weakness of specific muscles, hyperactive reflexes, incoordination (ataxia), and abnormal eye movements. The diagnosis of clinically definite MS requires documentation of two distinct episodes of symptoms and two or more signs evident on the neurological examination. Episodes of symptoms must last at least 24 hours and be separated by one or more months. Signs must be due to involvement of 2 or more separate parts of the brain and spinal cord. Electrophysiological tests called evoked potentials can be helpful in documenting involvement in more than one location in the CNS.

The diagnosis of MS can be difficult to establish, especially when the initial symptoms are unaccompanied by signs, abnormalities on MRI or electrophysiological tests, or analyses of spinal fluid. Even when the initial symptoms is accompanied by abnormalities on the neurological examination, it is still possible that the correct diagnosis is something other than MS. For this reason, MS is said to be a "diagnosis of exclusion". This means that other medical conditions must be considered and excluded before the diagnosis of MS can be made confidently. Medical conditions that can mimic MS include metabolic or vitamin deficiencies, unusual infections, inflammation of the blood vessels of the brain (arteritis), degenerative disorders of the nervous system, or cancers that have spread to the brain. This is why blood tests, X-rays, brain and spine MRI's, and spinal taps to analyze cerebrospinal fluid may be required before a diagnosis of MS can be made with certainty. In some cases, even after extensive testing, a confident diagnosis cannot be made and future developments must be awaited.

Diagnostic tests

Tests can facilitate the diagnosis of MS, particularly when there are fewer than two abnormal signs on the neurological examination. In this instance, an abnormal test can be used to document a second sign.

Magnetic resonance imaging (MRI): The brain MRI is the most sensitive test for detecting structural abnormalities due to MS-related disease activity. MRI scans show focal brain abnormalities in more than 90% of patients with clinically definite MS. The MRI scan can also distinguish between new or old lesions, and thus provides a measure of disease activity. The MRI is also useful for excluding other neurological conditions that might be confused with MS. Because the imaging abnormalities seen in MS patients can also be seen in other medical conditions, a diagnosis of definite MS cannot be based solely upon the MRI.



Evoked Potentials: Evoked potentials reflect changes in the electrical activity that occurs within the CNS due to sensory input (a stimulus). The electrical response to the stimulus is measured by electrodes applied to the scalp. Visual evoked potentials are obtained by stimulating the eye with a checkerboard pattern of light and dark squares that are alternated on a television monitor. Brain stem auditory evoked potentials are produced by click sounds applied through earphones. Somatosensory evoked potentials are produced by electrically stimulating nerves in the hands or feet. The time between application of the stimulus and occurrence of the evoked potential provides a measure of the nerve's ability to conduct electrical impulses from one point to another. If the response time is slowed, this suggests that the nerve pathway is not functioning properly as a result of demyelination. These tests are abnormal in 70-90% of patients with clinically definite MS and often detect abnormalities that are not apparent on neurological examination. Because these tests measure function within the brain or spinal cord, they complement the information about brain structure provided by the MRI.

Lumbar Puncture (Spinal Tap): Cerebrospinal fluid abnormalities are detected in 80-90% of patients with clinically definite MS. These abnormalities include an increase in the number of cells and immunoglobulin proteins suggesting an inflammation or a heightened immune response. This test may be used to establish a diagnosis in patients who have experienced a slowly progressive decline in function without exacerbations (i.e., patients with so-called primary progressive MS) and who have no abnormalities seen on the brain MRI scan. In such instances, a diagnosis of definite MS cannot be made without an abnormality in the spinal fluid. The spinal fluid analysis may also be useful in excluding an infection that may be difficult to distinguish from MS."