Diagnosis: A Misunderstood Word
|Copyright (c) 2008 by Kevin Thompson
The Meaning of Diagnosis
The concept of diagnosis (the identification of the nature and cause of
a disease, or injury) has a central role in medicine. It is a
familiar concept, as we are accustomed to visiting our doctor with a
problem, having some tests done, and coming away with a diagnosis
and treatment. Yet for all of its familiarity, the medical concept of
diagnosis does not mean what most people think it means, and the
difference between the perception of diagnosis, and the reality, leads
to confusion when the patient's problems have to do with mental
Suppose, for example, that you visited your doctor with a case of strep
throat, which is a sore throat caused by an infection of the
bacteria Streptococcus pyogenes
Your doctor would ask questions about your symptoms, examine your
throat, possibly order a throat culture or other test, provide a
diagnosis of strep throat, and prescribe an antibiotic to fight the
The strep-throat example contains all of the elements of a medical
visit that patients take for granted, including a diagnosis (strep
throat) that identifies the specific cause of the problem (its etiology
, in medical terms), which makes possible the selection of a specific treatment that is known to work.
Now, contrast the neat picture of strep throat with that of meningitis
, which is an inflammation of the membranes that cover the brain and spinal cord (the meninges
). Meningitis is diagnosed based on symptoms such as neck stiffness, fever, headache, and so forth.
Superficially, the diagnoses of strep throat and meningitis appear
similar: A doctor provides the diagnosis based on symptoms and tests.
However, there is a very important difference between the two diagnoses.
- In the case of strep throat, tests identify the specific cause of the illness (Streptococcus pyogenes), and the name of the diagnosis even reflects this cause. (I will call this an etiological diagnosis.)
- In the case of meningitis, the specific cause is usually unknown
(it can be any of numerous viruses or bacteria), and the name of the
diagnosis reflects not the cause of the disease, but its primary
effect, i.e. inflammation of the meninges. (I will call this a symptomatic diagnosis.)
These two examples reflect the fact that there are two types of
diagnosis: One identifies the specific cause of an illness, while the
other is essentially a name for a group of symptoms or effects. While
the diagnoses may seem similar to the patient, their implications for
choice and effectiveness of treatment are significant.
- An etiological diagnosis enables the doctor to prescribe a treatment that addresses the specific cause of the illness.
- A symptomatic diagnosis does not identify a specific cause, and
so the only options available to the doctor are those that offer
symptomatic relief (such as medicine to relieve pain, fever, and
swelling), or which may treat the underlying cause successfully, but
for reasons that are unknown (such as the treatment of malaria by
quinine, whose effectiveness was clear centuries before its mechanism
of action was understood).
Diagnosis and Mental Illness
The relevance of this discussion to mental illness is simple: Diagnoses
of mental illness are of the symptomatic type, not the etiological type. In
other words, the diagnosis of depression, bipolar disorder, or
schizophrenia is essentially a label applied to a set of symptoms that
commonly occur together. The diagnosis does not reflect the underlying
cause of the disorder (its etiology), and usually does not even involve
diagnostic techniques other than a review of the patient's symptoms and
The unfortunate truth is that the causes of serious mental illness
are not known. The various theories proposed to explain them, which
involve concepts such as neurotransmitter concentrations and
receptor densities, probably have some degree of validity, but they
cannot be tested in patients, and lack the specificity required to
design treatements that precisely address the causes.
Critics of the pharmacological (medication-oriented) treatments of
mental illness, such as the Church of Scientology, frequently claim
that the inability to provide a etiological diagnosis for any mental illness
invalidates both the diagnosis, and the justification for medications
used to treat the illness. Their claims make superficial sense, as the
cause of mental illness is unknown, but their conclusions are simply
In reality, most
of the ills we encounter on a daily basis not only
have unknown causes, but are treated without obtaining any kind of
diagnosis. Consider, for example, the person who takes nonprescription
pain medicine for an occasional headache, or a decongestant for the
"common cold" (another symptomatic diagnosis). Few people refuse to
seek symptomatic relief just because they cannot obtain an etiological
diagnosis of their discomfort, and rightly so. The fact that the
diagnosis of mental illness, and treatments available for it, are
symptomatic in nature, does not make the treatments useless! Many
people have discovered profound relief through effective psychiatric
medications, and live much happier lives as a result.
The Future of Diagnosis
Yet as useful as the concept of diagnosis has been for medicine, the
challenges raised by mental illness lead me to think that it is
becoming less relevant. Given the central nature of diagnosis to
medicine, this is a shocking concept. After all, how can we treat
illnesses that we cannot diagnose?
The short answer is that we are already
treating illnesses we cannot diagnose. The tidy categories of mental
illness provided in diagnostic guidelines, such as the DSM-IV, often do
not map neatly to the problems patients bring to their doctors. Just
how useful is a diagnosis if three different doctors can diagnose the
same patient as suffering from depression, anxiety, and bipolar
disorder? How meaningful is a diagnosis of depression if the effective
medication turns out to be an antipsychotic? While the diagnostic
labels have some value, they clearly do not provide reliable guidelines
to treatment. They are simply the best that we can do right now.
To the extent that we understand anything about the etiology of mental
illness, this situation is not surprising. One thing that
seems clear is that depression, schizophrenia, and other mental
illnesses do not typically arise from simple causes, such as a lesion
in one part of the brain, or a failure to produce enough of a
particular biochemical. Instead, they arise from abnormalities of
nerve-cell populations, neurochemistry, and electrical activities
distributed throughout much of the brain and nervous system. If so,
then there is no single, localized, identifiable cause for (say)
depression, even in principle. As a result, no medication can simply
cure the problem in the sense that an antibiotic can cure an infection.
A true cure would have to restructure the brain and nervous
system of the patient, in a fashion customized for each person, a
capability that is far beyond the medical science of today.
If neither diagnosis nor treatment can truly address the reality of
mental illness, then where does that leave us? Eventually, many decades
in the future, I suspect that genuine cures will become available, but in
the near term, we are limited to increasingly effective symptomatic
treatment, which is still of great value. The challenge, then, is to
find ways to optimize treatment for conditions that do not have precise
diagnoses. I will take up that challenge in the next issue of this
The popular conception of diagnosis as a precise description of an
illness and its cause, which enables precise treatment, has always been inaccurate.
It is true in many cases, and useful when true, but diagnoses
are often labels applied to groups of symptoms, and do not address
the specific cause of the illness.
Further, while diagnosis and treatment have long been partners in the
practice of medicine, the usefulness of that partnership is
weakening because of the particular challenges posed by mental
illness. The concept of diagnosis is not likely to disappear, but
alternative ways of thinking about illness are likely to become more
useful in the future. In the meantime, those of us who live in the
present can be grateful that symptomatic relief for mental illness,
while imperfect, can provide tremendous benefits.
Ph.D. is the author of Medicines for Mental Health: The
Ultimate Guide to Psychiatric Medication
You can find information about treatments for depression, bipolar
disorder, schizophrenia, and sexual problems on his Web site at