A dirty fact: "Approximately 1 in 20 people diagnosed with MS don't have MS."
There is no one test that can be done to diagnose MS. MS is diagnosed by combing a set of clinical and MRI findings, electric or neurophysiological investigations and laboratory tests. If these tests fulfil a set of so called MS diagnostic criteria the Healthcare professional (HCP) or neurologist makes a diagnosis of MS.
The underlying principle of making a diagnosis of MS is showing dissemination of lesions in space and time and excluding other possible diagnoses that can mimic MS. The diagnostic criteria have evolved over time from being based purely on clinical attacks, to those including electrical and spinal fluid tests, to the modern era in which we use MRI to help confirm dissemination in time and space.
Dissemination in time means to attacks or MS lesions occurring at least 30 days apart. Dissemination in space means lesions occurring in different locations, for example the optic nerve and spinal cord.
The electrical or neurophysiological tests are called evoked potential (EPs) and test electrical conduction in a particular pathway. They can be useful to show lesions in pathways that are not evident on the neurological examination or seen on MRI. The EPs can also show slow electrical conduction which is one of the hallmarks of diseases that affect myelin, the insulation of nerves that are responsible for speeding up electrical conduction.
MRI: The laboratory tests are typically done to exclude other diseases that can mimic MS. One test that is useful in helping making the diagnosis of MS is examining the spinal fluid for the presence of oligoclonal bands (OCBs), which are the fingerprint of a specific type of immune activation within the central nervous system (CNS). The OCB fingerprint is relatively specific for the diagnosis of MS in the correct clinical context.
VEPs: I have spent some time explaining this all to you as we neurologists get the diagnosis wrong in approximately 5% of MSers. In other words 1 in 20 people who have a diagnosis of MS in life don't have MS when their brains are studied at postmortem when the die. This data is based on a large study that looked at the brains of all people who died with a diagnosis of MS in a region of Denmark.
Why is the getting the correct diagnosis of MS so important? Firstly, some of the treatments we us in MS have life threatening complications; you don't want to expose people without MS to these complications. Some diseases that mimic MS can be made worse by MS DMTs. Finally, a diagnosis of MS has many psychological, social, financial and economic implications for people. Just having a diagnosis of MS, even if you turn out to have benign disease, has implications for the person concerned. For example, it may affect your life choices and may impact on your ability to get insurance cover to name to obvious examples. I would therefore advise you to make sure you have MS and not an MS mimic.
Common MS mimics:
The evolving definition of MS based on diagnostic criteria:
Clinical criteria only:
Clinical, EPs and CSF analysis:
Clinical, EPs, CSF analysis and MRI: