Early Diagnosis of Multiple Sclerosis: Difficult But Important
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