How
does one make a diagnosis of multiple sclerosis early in its course
when treatment can best prevent damage to the brain and spinal cord?
The succinct answer is: "With difficulty."
The principal dilemma in current management of multiple sclerosis is
that while early diagnosis enables damage-sparing treatment to begin,
diagnosing MS too early increases the likelihood of treating people who
don't actually have the disease. Current disease-modifying drugs are
all given by injection and cost about $14,000 per year. Apart from
being inconvenient and expensive, there is some risk of harm from them
which, if the patient doesn't actually have MS, occurs without any
offsetting benefit.
The dilemma would not be great if multiple sclerosis was easy to
diagnose, but unfortunately MS is among the most difficult diagnoses in
all of medicine to make, at least while still in its early stages.
Early in the course of symptoms, MS can resemble other conditions;
moreover, other conditions can resemble MS.
Affecting 2.5 million people worldwide and 350,000 people in the U.S.
alone, multiple sclerosis is not exactly a rare disease. It affects
women at least twice as often as men and begins early in adulthood with
most cases starting between the ages of 20 and 40.
MS is a so-called autoimmune disease, meaning that a person's immune
system--ordinarily useful and essential in fighting off
infections--becomes overactive and attacks the individual's own bodily
tissues. Rheumatoid arthritis is another example of an autoimmune
disease, but in MS the immune attack is not directed against joints as
it is in rheumatoid arthritis. Instead, the immune system attacks large
clusters of nerve-fibers generally deep within the central nervous
system which includes the brain and spinal cord.
These attacks can produce a wide variety of symptoms depending on what
the usual function was of the nerve-fibers that are under attack. When
the attacked nerve-fibers have to do with vision, the symptoms are
visual, like loss of visual clarity or even doubling of vision. When
the nerve-fibers are involved with the process of bodily sensation,
then the symptoms can be numbness or tingling. In fact, visual or
sensory symptoms are the most common initial symptoms in multiple
sclerosis. But initial symptoms might instead consist of dizziness,
weakness, clumsiness or difficulty with urination. The sheer diversity
of early symptoms that can be due to multiple sclerosis is one of the
chief difficulties in recognizing it for what it is and properly
diagnosing it.
It's useful in this regard to consider the twin issues of
"false-positives" and "false-negatives." In short, every medical test
and every diagnosis is subject to these errors. False-positive means
that a test or a doctor indicates that a disease is present when it is,
in fact, absent. A false-negative error occurs when a test or a doctor
indicates that a disease is absent when it is, in fact, present.
Despite the increased confidence that expanding medical knowledge and
ever-more sophisticated tests provide, false-positives and
false-negatives are a fact of life and still apply to every test and
every diagnosis.
In multiple sclerosis there are three cornerstones to the diagnostic
process. In usual descending order of importance they are the clinical
evaluation, magnetic resonance imaging (MRI) scanning and examination
of the cerebrospinal fluid. Each of these is important in its own way,
but one component almost never stands on its own merits, requiring one
or both of the other components for corroboration.
The clinical evaluation refers to the time-honored process in which the
physician elicits the history of the symptoms and performs a physical
examination. The physical examination consists mainly of the
neurological examination, which is a battery of mini-tests that
inventories the performance of different components of the nervous
system.
Even a test as high-tech and powerful as the MRI scan can lead to
diagnostic errors. False-positives often occur when a patient has a
scan for a totally unrelated reason--like headaches, for example--and
has pockets of increased signal within the brain for which the
radiologist raises the possibility of multiple sclerosis. When the
abnormal scan leads to consultation with a neurologist, the neurologist
often determines that multiple sclerosis is out of the question, and
the areas of increased signal are either benign or due to another
problem entirely. MRIs less frequently produce false-negatives for
multiple sclerosis, but even so, this imaging test is believed to show
just the tip of the iceberg in this disease, failing to demonstrate
important changes that occur at the microscopic level.
Examining the cerebrospinal fluid (CSF) is another valuable tool in
diagnosing MS. The CSF bathes the inside and the outside of the brain
and the outside of the spinal cord, so its cellular and chemical
composition often reflects what's going on within those structures. CSF
is obtained by means of lumbar puncture, also known as spinal tap, a
safe procedure in which a needle is inserted through the lower back and
into the CSF space. The fluid is collected as it drips out the back of
the needle. In cases of active MS there are usually abnormal proteins
produced by the immune system that can be detected and measured in the
CSF. However, here too there are false-positives and false-negatives,
so that some people with abnormal proteins don't have MS and other
people with normal proteins still do have the disease.
So the diagnostic process--including clinical evaluation, MRI scanning
and CSF examination--is fraught with the possibility of error at each
step of the way. Yet there is considerable incentive to make the
diagnosis as early in the disease as possible (which is also when the
risk of diagnostic errors is greatest) in order to initiate treatment
that tames the out-of-control immune system. Sifting through the
diagnostic information to make a timely and accurate diagnosis almost
always requires the assistance of a neurologist, and even with the help
of these specialists in disorders of the nervous system, sometimes the
diagnosis gets revised as time passes and clues become more definite.
(C) 2005 by Gary Cordingley
