There is no one test that will conclusively show that someone has MS and diagnosis usually involves a combination of investigations. Similarly, none of the individual symptoms people can experience are unique to the condition. This means that in order to reach a diagnosis, a range of other possible explanations has to be ruled out and so the process can be difficult and take some time.
The diagnosis of MS is made by a neurologist. To show that someone has MS, the neurologist is usually looking for evidence of two or more areas of scarring in different parts of the central nervous system that have occurred at different points of time.
Brain imaging or scanning is becoming more powerful and it is now technically possible to make a diagnosis based on information from one attack of symptoms and evidence of further disease activity from scans. However, it is still unusual to diagnose MS from just a single attack of symptoms.
A number of tests are used to try and find information to help a neurologist decide if someone has MS.
As the neurologist needs to establish that different symptoms have occurred at different times, a discussion of someone's previous symptoms and health is important in establishing a diagnosis of MS. Sometimes a previous episode of numbness or double vision, for instance, that might have passed of its own accord or been treated without thought of MS at the time can prove significant.
There are a number of simple tests that a neurologist can carry out that may suggest whether or not MS is a cause of symptoms. These include checks on movement, coordination, vision, balance, reflexes and other functions of the five senses. Information from these tests may also give an indication as to where in the central nervous system damage has occurred and which further tests might be useful.
Blood may be taken for testing. There is no blood test that can determine whether someone has MS, but if there are abnormalities, it is an indication that another condition may be present and might be causing symptoms.
Although the patient history and neurological examinations might suggest the diagnosis of MS, the process usually involves one or more tests to look for evidence of MS within the body.
Magnetic resonance imaging (MRI)
First used in MS in the early 1980s, MRI has become a key diagnostic test.
An MRI machine is essentially a large magnet, shaped as a tube, within which the person being scanned lies. The procedure is painless, although the machines can be noisy.
Images are created by using magnetic fields and radio waves to monitor the behaviour of hydrogen atoms in the body.
The nucleus at the centre of an atom spins like a top. The powerful magnetic field in an MRI machine (more than 10,000 times stronger than gravity) makes the atoms line up in the direction of the magnetic field.
The machine then fires a pulse of radio waves that causes the atoms to spin in a different direction (causing 'resonance'). When the pulse is turned off, the atoms return to their natural alignment within the magnetic field and release energy. The machine picks up this signal and sends it to a computer, which converts it into an image of a slice through the body.
Scars caused by MS show up as white patches on MRI images, giving a very clear picture of the effects of MS on the brain and spinal cord.
Depending on what the scan is looking for, some people may be injected with a contrast enhancing agent called gadolinium before a scan. This allows the MRI to show damage to the blood brain barrier, which indicates areas of active MS.
Preparing for an MRI scan
A lumbar puncture involves inserting a hollow needle into the base of the spine and drawing off a quantity of cerebrospinal fluid (CSF), the fluid that surrounds the brain and spinal cord within the skull and backbone.
In the diagnosis of MS analysis of cerebrospinal fluid is looking for:
White blood cells
Generally the number of cells from the immune system in the cerebrospinal fluid is low. For many people with MS the count of white cells in cerebrospinal fluid is up to seven times higher than normal. A count that is even higher than this is probably due to an infection of some sort, such as Lyme's Disease, and not MS.
In MS, cells from the immune system cross the blood-brain barrier and attack the myelin that surrounds nerves. As a result, the level of proteins from the immune system in the cerebrospinal fluid of someone with MS is higher than it should be and is higher than the level in the blood, a sample of which is also analysed.
The test that shows the presence of immune system proteins in cerebrospinal fluid is called electrophoresis. A sample of fluid is placed on a gel and voltage is applied. This causes proteins of the same size to bunch together, forming visible 'bands'.
One band (monoclonal) in the cerebrospinal fluid is normal. The term oligoclonal bands refers to the presence of two or more bands and shows the presence of disease activity. Whilst this does not necessarily mean that someone has MS, more than 80% of people with MS do have oligoclonal banding in their cerebrospinal fluid.
Evoked potentials are tests that measure the speed of nerve messages along sensory nerves to the brain.
The most commonly used test is called visual evoked potentials (VEP). Electrodes placed on the skin measure messages sent from the eyes in response to being shown a flashing chessboard pattern on a computer screen. Less frequently, tests of sensations from the skin (somatosensory evoked potentials), which involve tiny electric impulses, and of hearing (auditory evoked potentials), using clicks, can also be carried out.
Visual evoked potentials work on the basis that it is possible to measure how long it takes for input from the eye to get to the visual cortex at the back of the brain where this information is processed. As damage to the optic nerve in MS can slow messages down, evoked potentials tests can indicate the presence of an area of scarring that is not causing any obvious symptoms (described as clinically silent). Delays of as little as 10 milliseconds can indicate that there is damage to the nerve pathway.
- More information from the MS Trust
- Diagnosis - A to Z of MS
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