Diagnosing multiple sclerosis (MS) is not always easy. It may take some time from when symptoms first appear to confirm the diagnosis. MS is diagnosed when it is clear from neurological tests and a neurological examination that lesions are present in more than one area of the central nervous system (usually the brain, spinal cord, or the nerves to the eyes) and that damage has occurred at more than one point in time.

A diagnosis of MS is confirmed when you have a combination of:^{5, 6}

1. Two separate episodes of neurological symptoms-such as weakness or clumsiness, vision problems, tingling or numbness, or balance problems-that a neurologist can verify. Each episode must have lasted at least 24 hours and occurred at different times at least 1 month apart.
2. Symptoms that indicate injury to more than one part of the central nervous system, and MRI and laboratory tests that show abnormal findings consistent with a diagnosis of MS.
3. No other disease or condition that is clearly causing the symptoms and test results.

Your medical history and neurological examination can identify possible nervous system problems and are often enough to strongly suggest a diagnosis of MS. Tests may help confirm or rule out the diagnosis when your history and examination alone do not provide clear evidence of the disease.

Some people have had only one episode of a neurological symptom such as optic neuritis, but MRI tests suggest they may have MS. This is known as a clinically isolated syndrome. Many of these people go on to develop MS over time. MS is diagnosed when MRI tests done a few months apart show more than one area of neurological damage and when other tests are consistent with MS.

Tests used to diagnose MS

Magnetic resonance imaging (MRI) of the brain and spinal cord is done to confirm a diagnosis and help your doctor decide which treatment is best. More than 90% of people who have MS have an abnormal MRI result.⁷ For people in whom MS has already been diagnosed, MRI scans may also be used to follow the progression of the disease. MRI and neurologic examination may help doctors predict which people will develop MS after a first attack of symptoms.⁸ See an illustration of an MRI showing MS in the brain.

Lumbar puncture (sometimes called a spinal tap) may be done to evaluate cerebrospinal fluid. Most people with MS have abnormal results on this test, such as abnormal levels of a protein called immunoglobulin G (IgG) or a mild increase in white blood cells.

Evoked potential testing can often reveal abnormalities in the brain and spinal cord and in the optic nerves that a neurological exam and other tests may not be able to detect.

Tests used to diagnose accompanying conditions

Urinary tract tests may be needed to help diagnose a problem with bladder control in a person who has MS.

Neuropsychological tests may be needed to identify thinking or emotional problems, which may be present without the person being aware of them. Typically, these tests are in a question-and-answer format.