Differential Diagnosis of Substance Use Disorders
Wayne
G. Siegel, Ph.D., L.P.
Gary L. Fischler & Associates PA.
Differentiating between substance use disorders,
substance induced psychiatric disorders, and other mental illnesses
presents a common but difficult task for clinicians who conduct
assessments. Historically, far too many clients have been misdiagnosed
as mentally ill -- depressed, schizophrenic, bipolar, or personality
disordered -- when their symptoms were clearly attributable to
drug or alcohol use. Conversely, countless mentally ill clients
have had psychiatric symptoms falsely attributed to substance
abuse. In both cases, the misdiagnosis leads to negative outcomes,
with either the substance use disorder or mental illness left
untreated.
Differential diagnosis of substance use disorders
and mental illnesses involves inherent difficulties because
they co-occur to a very high degree. Data from the latest phase
of the Epidemiological Catchment Area (ECA) Study (NIMH, 1991),
suggest that of the estimated 16.7% of the U.S. population with
substance use disorders, more than half have at least one additional
comorbid mental disorder. Certain disorders are more prevalent
than others. The most common comorbid disorders are antisocial
personality disorder, anxiety disorders, mood disorders, and
schizophrenia.
The ECA data also indicate that of the 22.5%
of the U.S. population who have a diagnosed mental illness,
approximately 29 % also have a substance use disorder. A number
of disorders show a substantial comorbidity with substance abuse,
including antisocial personality disorder (83.6%), schizophrenia
(47%), anxiety disorders (24%), bipolar disorder (61%), major
depression (37%), and dysthymia (31%). Therefore, when evaluating
a client with an identified substance abuse problem, without
any additional information, you can assume there is a 50% chance
that a comorbid psychiatric diagnosis will also exist. In addition,
when evaluating a client with an identified mental illness,
you can assume there is a 29% chance that a comorbid substance
use disorder will also exist.
The ability of psychoactive substances to mimic
nearly all the symptoms listed in the DSM-IV (Diagnostic and
Statistical Manual of Mental Disorders - Fourth Edition) further
complicates the task of differential diagnosis. Without additional
information, it may be impossible to determine if the symptoms
reflect a naturally occurring mental illness or result from
psychoactive substance use. DSM-IV recognizes this very issue;
within each major diagnostic category (mood, anxiety, psychosis,
cognitive, etc.), it provides the option of indicating that
the disorder is "substance-induced," in effect forcing
the clinician to consider this diagnostic alternative.
Diagnosing mental disorders is not an exact science,
and there is no definitive way to determine whether or not a
particular psychiatric symptom is caused by substance use. However,
some general guidelines can help. For example, a good history,
including careful assessment of the onset and course of both
psychiatric symptoms and substance use, is essential. Unfortunately,
obtaining such a history can often be quite challenging unless
the client is an unusually reliable historian. The use of collateral
sources such as family, friends, co-workers, school records,
employment records, and medical records fill in the gaps and
provide valuable information.
Following a good history, assessing the following
issues can help clarify diagnosis:
1. Time of
onset. If the psychiatric difficulties began
prior to the substance use, then it is likely that a psychiatric
disorder exists.
2. Substance
use patterns. A psychiatric disorder likely
exists if the psychiatric symptoms persist during significant
periods of abstinence from substance use (three months or longer).
3. Consistency
of symptoms. If the nature and magnitude of
the client's symptoms and problems are qualitatively different
or beyond what one would expect given the amount and type of
substance used then a psychiatric disorder likely exists.
4. Family History.
Many psychiatric conditions have a strong hereditary component,
and a family history of mental illness can support the suspicion
that a particular client has a mental illness.
5. Response
to substance abuse treatment. Clients with
both psychiatric and substance use disorders often have significant
difficulty complying with traditional substance abuse treatment
programs and relapse during or shortly after treatment.
6. Client's
stated reason for substance use. Individuals
with a primary psychiatric diagnosis and secondary substance
use disorders will often say that they "medicate symptoms"
-- they drink to quiet auditory hallucinations, they use stimulants
to ease depression, they use alcohol or another depressant to
take the edge off anxiety or soothe a manic phase. Substance
use will likely exacerbate psychotic conditions, but this does
not mean that the psychiatric condition is substance induced.
Treating the disorder with medication and assessing the response
can also provide valuable information.
Unfortunately, psychological tests which are
often of significant value in clarifying diagnosis are not always
helpful in clarifying whether or not the disorder results from
substance use. Since many psychological tests mainly describe
symptoms, traits, and level of functioning at a particular point
in time, they cannot always determine whether or not the symptoms
are substance induced or exacerbated. However, some instruments,
such as the MMPI-2 MAC-R scale or the Wechsler Memory Scale
- Revised, can be helpful to the clinician in making a differential
diagnosis.
Differential diagnosis is often not an either/or
question, and the use of chemicals can affect mental disorders
to a varying degree. The DSM-IV recognizes the uncertainty associated
with these issues. If limited information precludes a firm diagnosis,
the term "Provisional" may be used to indicate the
lack of certainty. Although not part of the formal DSM-IV convention,
many clinicians also use the term "Rule Out" just
prior to a diagnosis to indicate that not enough information
exists to make the diagnosis, but it must be considered as an
alternative.
The terms "provisional" and "rule
out" can be particularly useful when trying to determine
whether or not a client's symptoms stem from substance use or
a psychiatric disorder. For example, if a particular client
reported symptoms consistent with both major depression and
alcohol dependence and had no significant periods of abstinence,
one may list the diagnoses as follows: "Major Depressive
Episode, Recurrent - Provisional" and "Rule Out -
Substance induced Mood Disorder." This convention would
alert others that the client's depressive symptoms may be caused
by alcohol and should continue to be assessed.
These guidelines are meant to help the clinician
deal with the uncertainty of "real world" problems.
There are no hard and fast rules in making these judgments.
The goal is to collect as much information as possible, weigh
the data, consider all the diagnostic alternatives, make the
best possible clinical judgment using the information available
at the time, and clearly communicate your findings, including
your level of certainty, to the party or parties who will use
this information.
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