Establishing a diagnosis and determining the type of MS doesn’t always happen right away. By definition, a diagnosis of MS must include evidence of disease activity separated in time and space. Sometimes this means that it can take a little while for a diagnosis to be confirmed. When diagnosing MS, doctors are looking for evidence of the lesions in the central nervous system caused by MS. Sometimes these lesions cause symptoms and the doctor can determine the location of the lesion by the symptoms it is presenting on physical examination. Sometimes lesions occur but don’t cause symptoms, and doctors use MRI and evoked potential testing to determine their location. MRI can also be helpful in showing lesions that have developed at different times.
The time leading to a diagnosis can be a difficult one. Uncertainty, worry for the future, symptoms that appear and disappear just before seeing the doctor, delays waiting for appointments and tests – all these things can cause upset and sleepless nights. For some, a diagnosis of MS comes as a relief from worries of something far worse imagined.
The history and neurological exam are the mainstay of diagnosis in MS. MRI, evoked potentials and very occasionally lumbar puncture, are tests that may be useful in confirmation when a diagnosis of MS is suspected.
» Magnetic Resonance Imaging
Magnetic Resonance Imaging (MRI) is a medical imaging technique commonly used in radiology to visualize the internal function and structure of the body. MRI does not use radiation. MRI uses powerful magnetic fields to align the hydrogen atoms found in the body’s water molecules. In MS, the MRI can provide pictures of the areas of damage (lesions) in the central nervous system(CNS), caused by MS, and can also reveal whether there a loss of brain volume. If the contrast agent gadolinium is used, the MRI can image active inflammation that may be going on in the CNS. In early MS, it is possible, though uncommon (about 5%) to have a normal appearing MRI picture. Over time, with repeat MRI, characteristic lesions do appear, and if not, the diagnosis of definite MS must be reconsidered. If a second MRI is needed to confirm the diagnosis, it is important that it is done after a sufficient period of time since the last one, usually at least 3 months.
» Evoked Potentials
Evoked Potentials (EP’s - visual, auditory and somatosensory) is a test that measures the speed of nerve impulse conduction in the pathways of the central nervous system(CNS). In MS, nerve impulse conduction is slowed related to the myelin damage, and EP’s can record this slowing. The test involves placing small electrodes at spots on the head and body. A series of stimuli such as flashing lights or patterns, clicking sounds or very small electric shocks are applied. The EP test records how fast these stimuli are registered in the appropriate part of the CNS. Most people find the test painless, although occasionally a few find the electric shock to be a little uncomfortable very briefly.
» Lumbar puncture
Lumbar puncture (LP), sometimes known as a spinal tap, is seldom done since the development of the less invasive technologies, namely MRI and evoked potential technology. LP can be helpful in certain cases however, especially when other investigations are negative. During an LP, a small needle is inserted at the base of the spine, to sit in the space between the lining of the CNS, and the spinal cord itself. A small amount of the cerebrospinal fluid (CSF) which bathes the CNS and circulates through this space is collected. This fluid is examined for the presence of proteins which are known to be present with inflammation in the CNS.
It is important to remember that there is no one test that can be used to diagnose MS. The diagnosis of MS is one made only once other potential causes for symptoms have been ruled out. In addition, there are clear diagnostic criteria which must be met for a diagnosis of definite MS to be made.