So let us start from where we left off. Just how do we (doctors) go about making (confirming) the diagnosis of MS.
MRI scan: Well one of the test most commonly requested (infact done in nearly every patient) is a MRI scan of the brain and at times of the cervical spinal cord. What are we looking for you may ask? Well multiple sclerosis on the MRI is characterized by plaques (lesions) which are disseminated in space and in time. What does that mean? In a typical patient of MS, the MRI scan shall show evidence of disease activity which is scattered around in different parts of the brain. Meaning there are MS lesions seen in different parts of the brain white matter (typically MS is a white matter disease though recent research indicates involvement of the grey matter too). So for example a typical MRI scan shall show plaques scattered in the white matter of the frontal lobe, parietal, temporal lobe, cerebellum and so forth. Moreover the MRI scan shall indicate that these plaques are of different age (which indicates that the disease has been present for sometime now). Remember what I said –relapsing and remitting MS. Sometimes to help secure the diagnosis, your doctor shall also order a MRI scan of the spine most commonly cervical spine. The intention is the same and that is to see evidence of dissemination of the disease process in the brain and spinal cord.
Spinal tap: a lumbar puncture is usually carried out. Does every patient need a spinal tap to help secure the diagnosis of MS? No. Remember the diagnosis of MS can be made clinically in some patients. In patients where the characteristic history is not forthcoming and in whom the MRI scan does not prove helpful (does not evidence of dissemination of disease process in space and time), a spinal tap may be warranted. The spinal fluid of MS patients is analyzed for certain proteins which suggest evidence of disease process. These include myelin basic protein (MBP), oligoclonal bands (OCBs) and IgG index.
Other tests: these tests may be requested in special circumstances (usually when the diagnosis remains elusive inspite of MRI scans and spinal tap).
1) Visual evoked potential (VEP), brainstem auditory evoked potential (BAEP) and somatosensory evoked potentials (SSEP): these tests usually involve testing the integrity of different pathways in the brain. VEP tests the visual pathway from the eye to the occipital (visual) cortex, BAEP–tests the brainstem auditory pathways while SSEP check for the integrity of the white matter tracts carrying somatosensory information (vibration, joint sense and position sense) from the periphery (arm or leg) to the somatosensory cortex. MS lesions involving any of these pathways cause a delay in the rate of conduction of nerve impulse and provide ancillary evidence of involvement of white matter tracts of the brain by a demyelinating disease process.
I hope these two posts help you all in understanding how the diagnosis of MS is made.
Nitin Sethi, MD