There is no single test that is proof-positive for diagnosing multiple sclerosis. However, there are accepted criteria for making the diagnosis, but even this system is imperfect.
Since diagnosing MS can be very difficult, a neurologist who specializes in treating MS should evaluate your symptoms. As many as 10% of people diagnosed with multiple sclerosis actually have some other condition that mimics MS. Examples of other conditions that masquerade as MS include inflammation in the blood vessels, multiple strokes, vitamin deficiency, lupus, or a brain infection. Sometimes stress-related disorders can lead to a misdiagnosis of MS.
An accurate diagnosis of multiple sclerosis is based on your medical history and a neurological exam (an exam of the function of the brain and spinal cord) using various tests. A lot depends on the skill of the doctor in asking the right questions to uncover information and to properly evaluate the signs and symptoms of a malfunctioning brain or spinal cord.
In addition to a thorough medical history and exam, a variety of specialized procedures are helpful in accurately diagnosing MS. These include imaging techniques, such as MRI, spinal taps or lumbar punctures (examination of the cerebrospinal fluid that runs through the spinal column), evoked potentials (electrical tests to help determine if MS has affected a person's nerve pathways), and lab analysis of blood samples.
What Are the Accepted Criteria for a Diagnosis of Multiple Sclerosis?
Multiple sclerosis usually begins between 20 and 50 years of age
Symptoms and signs indicating disease of the brain or spinal cord
Evidence of two or more lesions -- or abnormal areas on the brain -- from a MRI scan
Objective evidence of disease of the brain or spinal cord on doctor's exam
Two or more episodes lasting at least 24 hours and occurring at least one month apart
No other explanation for the symptoms
What Does an MRI Show?
MRI is the best test to view the changes caused by multiple sclerosis. The precise image produced by MRI gives the neurologist clear evidence of inflammation in the deep parts of the brain or spinal cord that is characteristic of MS.
However, abnormal spots on the brain MRI can be caused by other conditions, so before making a diagnosis your doctor will consider all information including your symptoms and scan results. Similar lesions can be seen in older people or people with high blood pressure and diabetes.
Also, a normal MRI does not absolutely rule out a diagnosis of MS. About 5% of patients who are confirmed to have MS on the basis of other criteria, do not have lesions in the brain on MRI. These people may have lesions in the spinal cord or may have lesions that cannot be detected by MRI.