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Doctors do not have a specific test which tells them that a person has multiple sclerosis. It can therefore be very difficult for a doctor to be sure that somebody’s symptoms are due to multiple sclerosis. The most important means by which a doctor makes the diagnosis is by listening carefully to the person’s description of their symptoms (the history), and then examining the nervous system carefully to look for any signs of things not working as they should (the neurological examination). Even with all of today’s technological advances in medicine it is still the history and neurological examination which are most helpful to doctors to help them try and decide whether or not somebody is affected by multiple sclerosis.

However, there are some tests, which give very helpful additional information, although none of these tests on their own can give a diagnosis of multiple sclerosis. Sometimes the abnormalities which are picked up by these tests can be found in other conditions as well as multiple sclerosis.

MRI scan
MRI scan or Magnetic Resonance Imaging is an investigation which has largely taken over from X-rays as a means to get good pictures of the brain. MRI scans of the brain allow doctors to see the small areas of scarring (sclerosis) which are one of the features of MS. Over 95 per cent of people with MS are found to have such abnormalities on a brain MRI scan, so this can be a very useful test. Sometimes the doctor may arrange an MRI scan of the spinal cord; this can also be helpful for diagnosis, especially if most of the symptoms are coming from the spinal cord.

Examination of cerebrospinal fluid
Cerebrospinal fluid (CSF) is the clear fluid that circulates around the brain and the spinal cord. In multiple sclerosis it is often possible to identify abnormalities in the cerebrospinal fluid which may point to a diagnosis of multiple sclerosis: about 90 per cent of people with MS have extra bands of protein in the fluid called oligoclonal bands. Cerebrospinal fluid is usually collected by performing a lumbar puncture (known as a spinal tap in America). A small needle is passed through the skin of the back and between the bones of the lower part of the spine to obtain a small quantity of the fluid that is circulating around the spinal cord.

Evoked potential recording
This is a special group of tests done by neurology specialists, which allow them to measure how efficiently nerves are conducting impulses. The most commonly performed test in this group is called visual evoked potential recording or VEPs. Doctors stimulate the nerves at the back of the eye by asking the person to look at a flashing television screen showing a chequerboard. They then measure how long it takes for the impulses picked up by the eye to be transmitted to the part of the brain that deals with vision. In some people with multiple sclerosis there is an abnormal delay in the transmission of these impulses.

Unfortunately, none of the three groups of tests described here are completely precise and abnormalities are found on MRI scans and in the cerebrospinal fluid in many other conditions as well as multiple sclerosis. This is why it is sometimes difficult for doctors to be certain whether or not somebody has multiple sclerosis, particularly in the early stages of the condition.