There is no single test that unequivocally detects
MS. When faced with a patient whose symptoms,
neurological exam results, and medical history
suggest MS, physicians use a variety of tools to
rule out other possible disorders and perform a
series of laboratory tests which, if positive,
confirm the diagnosis.
Imaging technologies such as MRI can help locate
central nervous system lesions resulting from myelin
loss. MRI is painless, noninvasive, and does not
expose the body to radiation. It is often used in
conjunction with the contrast agent gadolinium,
which helps distinguish new plaques from old.
However, since these lesions can also occur in
several other neurological disorders, they are not
absolute evidence of MS.
Several new MRI techniques may help quantify and
characterize MS lesions that are too subtle to be
detected using conventional MRI scans. While
standard MRI provides an anatomical picture of
lesions, magnetic resonance spectroscopy (MRS)
yields information about the brain's biochemistry;
specifically, it can measure the brain chemical N-acetyl
aspartate. Decreased levels of this chemical can
indicate nerve damage.
Magnetization transfer imaging (MTI) is
able to detect white matter abnormalities before
lesions can be seen on standard MRI scans by
calculating the amount of "free" water in tissues.
Demyelinated tissues and damaged nerves show
increased levels of free" (versus "bound") water
Diffusion-tensor magnetic resonance imaging
(DT-MRI or DTI) measures the random motion of water
molecules. Individual water molecules are constantly
in motion, colliding with each other at extremely
high speeds. This causes them to spread out, or
diffuse. DT-MRI maps this diffusion to produce
intricate, three-dimensional images indicating the
size and location of demyelinated areas of the brain.
Changes in this process can then be measured and
correlated with disease progression.
Functional MRI (fMRI) uses radio waves and
a strong magnetic field to measures the correlation
between physical changes in the brain (such as blood
flow) and mental functioning during the performance
of cognitive tasks.
In addition to helping scientists and physicians
better understand how MS develops-an important first
step in devising new treatments-these approaches
offer earlier diagnosis and enhance efforts to
monitor disease progression and the effects of
Other tests that may be used to diagnosis MS
include visual evoked potential (VEP) tests and
studies of cerebrospinal fluid (the colorless
liquid that circulates through the brain and spinal
cord). VEP tests measure the speed of the brain's
response to visual stimuli. VEP can sometimes detect
lesions that the scanners miss and is particularly
useful when abnormalities seen on MRI do not meet
the specific criteria for MS. Auditory and sensory
evoked potentials have also been used in the past,
but are no longer believed to contribute
significantly to the diagnosis of MS. Like imaging
technologies, VEP is helpful but not conclusive
because it cannot identify the cause of lesions.
Examination of cerebrospinal fluid can show
cellular and chemical abnormalities often associated
with MS. These abnormalities include increased
numbers of white blood cells and higher-than-average
amounts of protein, especially myelin basic protein
and an antibody called immunoglobulin G.
Physicians can use several different laboratory
techniques to separate and graph the various
proteins in MS patients' cerebrospinal fluid. This
process often identifies the presence of a
characteristic pattern called oligoclonal bands.
While it can still be difficult for the physician
to differentiate between an MS attack and symptoms
that can follow a viral infection or even an
immunization, our growing understanding of disease
mechanisms and the expanded use of MRI is enabling
physicians to diagnose MS with far more confidence
than ever before. Today, most patients who undergo a
diagnostic evaluation for MS will be classified as
either having MS or not having MS, although there
are still cases where a person may have the clinical
symptoms of MS but not meet all the criteria to
confirm a diagnosis of MS. In these cases, a
diagnosis of "possible MS" is used.
A number of other diseases may produce symptoms
similar to those seen in MS. Other conditions with
an intermittent course and MS-like lesions of the
brain's white matter include polyarteritis, lupus
erythematosus, syringomyelia, tropical spastic
paraparesis, some cancers, and certain tumors that
compress the brainstem or spinal cord. Progressive
multifocal leukoencephalopathy can mimic the acute
stage of an MS attack. Physicians will also need to
rule out stroke, neurosyphilis, spinocerebellar
ataxias, pernicious anemia, diabetes, Sjogren's
disease, and vitamin B12 deficiency. Acute
transverse myelitis may signal the first attack
of MS, or it may indicate other problems such as
infection with the Epstein-Barr or herpes simplex B
viruses. Recent reports suggest that the
neurological problems associated with Lyme disease
may present a clinical picture much like MS.
Investigators are continuing their search for a
definitive test for MS. Until one is developed,
however, evidence of both multiple attacks and
central nervous system lesions must be found before
a diagnosis of MS is given.