How is MS diagnosed?

Everyone's experience of diagnosis is different. You may have had a sudden, severe attack which demanded hospital attention and found that a diagnosis of MS followed very quickly.

However, MS is often difficult to diagnose so it may have taken you a long time to get to a definite diagnosis. All the symptoms of MS are seen in other health conditions so your doctors had to work out which one you have. This can mean having many tests to rule out other possibilities and then more tests to see if you have MS. It is sometimes a question of watching and waiting to see how your symptoms develop as this can help distinguish MS from other conditions. All this can be very frustrating and worrying but it is quite a common experience. 

You may have been given another diagnosis which later turned out to be wrong or maybe you were told that the cause of your symptoms couldn't be found. Perhaps this was hard to accept especially if it was years before you were given the correct diagnosis. 

It can be hard to understand why your diagnosis took so long but it is often a tricky call to make so usually no one, including you, was to blame.

There's no simple test for MS which can give you a 'yes' or 'no' answer like a pregnancy test. Neurologists have to take a multi-pronged approach and use their experience to decide if it's MS or not. Sometimes, it's impossible to be absolutely certain.

Here we discuss the different tests that are used in diagnosis, and what they might show. You can find more information about each test in our A-Z of MS.

Although a blood test cannot be used to diagnose MS, you may be asked to have blood tests to rule out other conditions that have similar symptoms.

You may have encountered unusual symptoms over many months or years. Your symptoms may have improved or gone away after a while, and seemed unimportant at the time. Perhaps you found other, very reasonable explanations. For example, being incredibly tired could be due having to a new baby in the family. Stumbling more could be due to getting older.

If you are seeking a medical opinion, do tell your doctor about any odd symptoms, such as numbness or blurred vision, that you may have had over the years. Your neurologist will review your test results alongside your medical history to decide if it adds up to a diagnosis of MS.

There are a number of simple tests that a neurologist can carry out that can suggest, or rule out, MS as a cause of symptoms. These include checks on your movement, coordination, vision, balance and reflexes. These tests not only suggest whether you might have MS, but can also indicate where in the central nervous system damage has taken place. They can usually be done in an ordinary clinic room, and no special preparation is needed.

Although your medical history and neurological examinations might suggest a diagnosis of MS, the neurologist will usually request one or more tests to look for evidence of MS within your body in order to be sure.

The most common next step is to have a scan of your brain and/or spinal cord using MRI (magnetic resonance imaging). This scan can detect the scars used by MS which show up as little white patches and are usually called lesions. Everyone gets more white patches in their brain as they get older so the neurologist has to judge if they are all age-related or possibly due to MS.

Sometimes a dye is injected into your vein before the scan as it can help the radiologist and neurologist distinguish between active MS lesions and old areas of scarring.

You may be asked to have a lumbar puncture where they take out a small amount of the fluid which bathes your brain and spinal cord (cerebrospinal fluid, or CSF). This is analysed in the laboratory to see if the fluid contains unusual antibodies, fragmented myelin nerve coating or an unusual amount of white blood cells. These findings might suggest MS or an alternative diagnosis. 

You may also have evoked potential tests. This involves putting small electrodes on your head, arms or legs to measure the speed of messages travelling along your nerves from your eyes, ears or skin on your limbs. If the messages are slowed then this may be due to MS.

The neurologist is looking for signs of scarring in your brain or spinal cord (the central nervous system). For a diagnosis of MS there needs to be two or more areas of scarring. These need to have happened at different points in time.

Although MRI scans can sometimes show enough evidence to make a diagnosis, it is still unusual to diagnose MS from just a single episode of symptoms.

The most commonly used guidance for making a diagnosis of MS is called the McDonald criteria.