CME
Approaches to psychiatric nosology: A viewpoint
Ajit Avasthi, Siddharth Sarkar, Sandeep Grover
Department of Psychiatry, Post Graduate Institute of Medical Education and Research, Chandigarh, India
ABSTRACT
Psychiatric nosology is required for communication among clinicians and researchers, understanding etiology, testing
treatment efficacy, knowing the prevalence of the problems and disorders, healthcare planning, organizing the services,
and reimbursement purposes. Many approaches have been used for psychiatric nosology, including categorical,
dimensional, hybrid, and etiological. The categorical approach considers illness as being either present or absent, and
similarity with prototypical description of a disorder is taken as a marker for the disorder. The dimensional approach
regards that symptoms of disorder exist on a continuum from normal to severely ill. The hybrid approach combines
categorical and dimensional approaches, with categorical diagnosis for broad diagnostic group and dimensional
indicator for severity. The etiological approach tends to find “reason” for the set of symptoms, which could be
biological, psychological, or social. In this article, certain critical issues about the different nosological approaches are
discussed. Hybrid approach currently seems to be the most preferred for widespread usage. In conclusion, psychiatric
nosology needs to evolve through epistemic iteration leading to successive changes and devising a more refined and
useful system with time.
Key words: Classification, disorders, nosology
INTRODUCTION
EVOLUTION OF PSYCHIATRIC NOSOLOGY
One needs nosology for a variety of purposes. It is required
for communication among clinicians and researchers about
what constitutes a particular disease and what does not.
It is needed to further the research for understanding
etiology, by having a set of symptoms being called as a
disorder. It is needed to understand the treatment efficacy
of various interventions, as one set of symptoms may
respond to an agent while another set may not. Nosology
is also useful to understand the prevalence of the problems
and disorders, so that appropriate healthcare planning can
be done. Moreover, it is required for insurance purposes
while deciding what kind of disorders should be under the
ambit of reimbursement. Hence, nosology cannot be done
away with, and is in fact required for scientific application
of the field.
Before one takes a critical look at the different approaches
to psychiatric nosology (a classification or list of diseases),
it would be worthwhile to look at the evolution of nosology
and the purposes served by it. The nosology of psychiatric
disorders has evolved over time. Beginning from the times
of Hippocrates and Aristotle, attempts have been made to
categorize and delineate various psychiatric disorders.[1,2]
Hippocrates and his followers classified mental illnesses into
various disorders, including mania, melancholia, paranoia,
and phobias; which were assumed to occur due to imbalance
in four humors. Pinel reduced all mental illnesses to four
basic types.[3] Karl Kahlbaum and Ewald Hecker developed a
descriptive categorization of syndromes, employing terms
such as dysthymia, cyclothymia, catatonia, paranoia, and
hebephrenia.[3] Emil Kraepelin grouped together a number
Address for correspondence: Prof. Ajit Avasthi,
Department of Psychiatry, Postgraduate Institute of
Medical Education and Research, Chandigarh, India.
E‑mail: drajitavasthi@yahoo.co.in
How to cite this article: Avasthi A, Sarkar S, Grover S.
Approaches to psychiatric nosology: A viewpoint. Indian J
Psychiatry 2014;56:301-4.
Indian Journal of Psychiatry 56(3), Jul‑Sep 2014
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DOI:
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of existing diagnoses and proposed 15 categories of mental
illnesses.[4] He suggested the dichotomy of dementia praecox
and manic‑depressive insanity, and proposed disorders
like psychogenic neurosis, psychopathic personality,
and syndromes of defective mental development. The
initial versions of Diagnostic and Statistical Manual
and International Classification of Diseases (DSM‑I and
DSM‑II, and ICD‑7 and ICD‑8) were based upon clinical
description of cases. There was a psychodynamic tilt in the
classification system. The DSM‑III (1980) and ICD‑9 (1975)
represented a shift from the previous classificatory systems
to a criteria‑based diagnosis, which led to widespread
usage of the classification systems in research and clinical
practice. Subsequently, classification systems incorporated
new entities in the later editions (DSM‑IV, DSM‑IV TR, and
ICD‑10).[5‑7] The DSM‑IV TR and ICD‑10 are the currently most
widely used nosological systems in psychiatric practice.
APPROACHES TO PSYCHIATRIC NOSOLOGY
Many nosological approaches to diagnosis have been
considered for the understanding of the disorders. These
prominently include categorical approach, dimensional
approach, and hybrid approach among others. Other
approaches that have been considered from time to time
include etiological approach to classification. Herein we
consider the various approaches and examine their uses
and pitfalls [Table 1].
We take a sample case for exploring the various approaches.
Mr. A, a 40‑year‑old banker, has symptoms of persistent
and pervasive sadness for about a month now. He fatigues
easily and has less interest in activities, as compared to his
previous self. His appetite has reduced and he has decrement
in sleep. He expresses ideas of guilt and pessimistic views of
future, but denies any suicidal ideas. He manages to go to
work, but has poor efficiency. He has no significant medical
illnesses. This is a case of what psychiatrists would usually
label as a depressive disorder as per the current nosological
systems.
CATEGORICAL APPROACH
This approach considers illness as being either present or
absent. Depending upon the similarity with the prototypical
description of a typical case, the disorder is labeled to be
either present or absent. For a particular case, the set of
symptoms either constitutes a disorder or not, and there
are no “in between” diagnoses. According to this approach,
there may be a large number of disorders depending on the
prototypes and descriptions. If symptoms of two disorders
are present, then the two disorders are said to be present
as comorbid disorders (e.g., generalized anxiety disorder
and depressive disorder existing as comorbid disorders).
According to the categorical approach, disorder is distinct
from normalcy (i.e., either one is ill or not ill).
Conceptualizing our case according to categorical
approach, Mr. A has depressive disorder which is distinct
from “normal” functioning. It is an entity separate from
dysthymia, depression not otherwise specified, and
anxiety disorders which are taken as other disorders. With
treatment if he improves adequately, he would not be
depressed (i.e., depression will either be present or absent).
Many problems are encountered with the categorical
approach. One of the major issues faced is determining
the threshold of symptoms that determines the diagnosis.
The threshold at which a diagnosis is made depends upon
the individual assessor’s conceptualization and sensitivity
to individual symptoms. Considering our case, should
depression be diagnosed when patient is sad 8 h a day, 14 h
a day, or 20 h a day? Should depression be diagnosed when
patient is somewhat sad, moderately sad, or intensely sad?
Another problem with the categorical approach is that of
sub‑syndromal symptoms. Symptoms of a disorder usually
present at a variety of levels of severity. It has been seen that
sub‑syndromal symptoms are associated with dysfunction
and disability, and treating them leads to improvement.[8]
But as they fall below a diagnostic threshold, no diagnosis
Table 1: Psychiatric nosology systems: Summary
Salient
features
Issues
302
Categorical approach
Dimensional approach
Hybrid approach
Considers illness as being either present or
absent, no “in betweens”
Similarity with prototypical description of a
disorder is taken as a marker for the disorder
If symptoms of two disorders are present,
then the two disorders are comorbid
Threshold of diagnosis
What to do with sub‑syndromal symptoms?
How should prototypical case be defined?
Delimitation from other disorders
Hierarchy of diagnosis
Symptoms of disorder exist on a continuum
from normal to severely ill
Dimensionality can be envisaged in terms of
number (count) of symptoms and severity of
each symptom group
A combination of categorical and dimensional
approaches
Categorical for broad diagnostic group
Dimensional for severity
Can all mental illnesses be defined on a few
dimensions or have different dimensions for
each disorder?
For a particular disorder, whether to take
only one dimension of severity or multiple
dimensions
When to treat/intervene when symptoms are
in continuum
Combines the issues of categorical and
dimensional approaches
Cutoff on a dimensional (severity) scale
measure to transform to a categorical diagnosis
is based on expert consensus for practical
purposes
Indian Journal of Psychiatry 56(3), Jul‑Sep 2014
Avasthi, et al.: Approaches to psychiatric nosology
would be made according to categorical approach,
and consequently there would be no intervention or
reimbursement for the same.
What constitutes a prototypical case may also be a matter
of contention. The conceptualization of prototypical case
may vary between experts and centers.[9,10] Whether a
case fits a diagnosis depends upon what cluster of signs
and symptoms are taken for making the diagnosis, and the
agreement between assessors (as measured by kappa) may
not concur on whether a patient has a psychopathology or
diagnosis.
Challenges may also be faced while delimiting from other
disorders. If two sets of symptoms (of two disorders)
are present, then are they two different syndromes (e.g.,
depressive disorder and generalized anxiety disorder) or
the combination should be considered a different syndrome
(e.g., schizoaffective)? Often psychiatric disorders are
comorbid with others, raising the issue that whether
segregation into pigeonholes is the right approach.[11‑13]
Since some of the symptoms of a disorder are frequently
encountered in another disorder, hierarchy of diagnosis
has been proposed.[14] Presence of a disease higher in the
hierarchy subsumes symptoms of disorder lower in the
classification. This leads to diagnostic quandaries. For
example, if a patient has symptoms of both schizophrenia
and depression, then should depression be coded separately
as a diagnosis or should only diagnosis of schizophrenia be
considered (being higher in the hierarchy of diagnosis)?
It has been suggested that the evidence for hierarchy is
minimal,[15] implying that disorders should be coded as
comorbid.
DIMENSIONAL APPROACH
According to this approach, symptoms of disorder exist on a
dimension which is a continuum from normal to severely ill.
Dimensionality can be envisaged in terms of number (count)
of symptoms (e.g., five out of eight symptoms to diagnose
major depressive disorder) and severity of each symptom
group (e.g., positive, negative, disorganized, cognitive,
affective dimensions of schizophrenia).
A disorder with three or more ordinal categories (e.g., mild,
moderate, and severe) can be said to have a dimensional
approach. Scales such as Hamilton Depression Rating
Scale (HDRS) represent a dimensional evaluation. The
dimensional approach suggests that symptoms may
be present in normal as well as in ill. A cutoff is used to
ascertain the threshold of diagnosis (which transforms the
disorder into categorical).[16] The diagnostic threshold is
determined by the expert’s opinion.
Conceptualizing the present case of Mr. A according to the
Indian Journal of Psychiatry 56(3), Jul‑Sep 2014
dimensional approach, sadness exists on a continuum with
severity ranging from normal to severely pathological. The
grading of individual symptoms and overall sadness can be
done using HDRS, and a cutoff score of >7 on HDRS is used
for diagnosing depression. The treatment response can be
monitored by using the severity scales.
Challenges are faced while using the dimensional approach
as well. Can we describe all mental illnesses on few
dimensions or do we need to have different dimensions
for each disorder? A related question posed is that for a
particular disorder, whether to take only one dimension
of severity or multiple dimensions of symptom sets. In our
case, the question is whether to have a separate dimension
for depression or a combined set of dimensions for all
disorders (like depressive symptoms, psychosis, biological
functioning, etc). Also, whether to use one dimension
of severity (e.g., HDRS) or to use multiple dimensions
describing different symptoms like sadness, cognitive
symptoms, and biological function.
Also, when symptoms are on continuum, then when should
they be treated or intervened with? Improvement in
low‑grade symptoms (when they approach normalcy) is less
with medication.[8] Treating everyone with any degree of
symptoms is not cost‑effective from public health viewpoint.
Hence, using a purely dimensional approach may not offer
assistance in making healthcare and clinical decisions.
HYBRID APPROACH
Hybrid approach represents a combination of categorical
and dimensional approaches. It utilizes categorical approach
for broad diagnostic group and dimensional approach for
severity of the disorder. The present‑day ICD and DSM use
this approach to some extent. The diagnosis of depressive
episode suggests a broad categorical diagnosis, while
ratings of severity into mild, moderate, and severe represent
dimensionality. However, both ICD‑10 and DSM‑IV TR tend
to use categorical approach to a larger extent.
The upcoming DSM‑5 is likely to use hybrid approach
more effectively.[17,18] A categorical diagnosis will still be
made (e.g., schizophrenia spectrum and other psychotic
disorders), but an additional dimensional construct would
be applicable for most disorders to convey severity (ratings
on a 0-4 scale on various symptoms cross‑sectionally, with
severity assessment based on past month). The DSM‑5, which
is in field trials at the time of writing, retains the categorical
diagnosis but introduces dimensionality on a larger scale.
Conceptualizing the case of Mr. A from the hybrid
perspective, categorical diagnosis would be of major
depressive disorder – single episode, while severity would
be measured by clinical global impression (CGI) of the past
1 week (rated from 0 to 7). Progress can be measured by
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Avasthi, et al.: Approaches to psychiatric nosology
change in CGI over time. Even when episode is in remission,
sub‑syndromal symptoms can be measured using CGI.
The hybrid approach also has its share of problems.
It combines the issues of dimensional and categorical
systems. It can be seen as a compromise approach that does
not have clear biological reasoning. For practical purposes,
the cutoffs agreed for a scale to make diagnosis are based
on a decision of experts, and they do not reflect presence
or absence of illness in a true sense. Also, there is difficulty
in reliably measuring psychiatric constructs, which may lead
to inaccuracies in diagnosis and severity assessment.
OTHER APPROACHES
The etiological approach tends to find “reason” for the set of
symptoms. The reasons could be biological, psychological,
or social. This approach has been suggested time and over
in the past. It has been propounded persuasively for some
psychiatric disorders like autism.
However, the etiological approach is difficult to use for
psychiatric disorders with the present understanding of
etiology (which is usually multifactorial). Interplay of genetic
and environmental factors is implicated in development of
most disorders. Role of each factor can be hardly quantified
with certain degree of precision. Also, it may be unclear
whether a factor causes the disorder or merely unmasks it
in susceptible individuals.
likely to be influenced by views of experts and political
influences. The most illustrative example is the inclusion
of homosexuality as a disorder and then its removal as a
disorder. Hence, psychiatric classification systems are likely
to have “wobbly” (back and forth) iterations. The present
system has evolved over the ages, incorporating the scientific
knowledge gained and practicalities adhered to. The system
is not a perfect one, but serves a lot of purpose. It is expected
that with time, a more refined and useful system will evolve
on the strength of further research findings.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
9.
WHICH APPROACH IS THE BEST?
10.
Hybrid approach seems to the most useful currently from
various standpoints. It is useful to the clinicians using the
categorical aspects of the classificatory system for making a
diagnosis. It helps researchers who are more interested in
the dimensional aspects to assess treatment response and
ascertain etiology. It helps administrators and healthcare
planners who use both categorical and dimensional aspects
to make decisions. It also helps patients and caregivers
to imbibe proper information (both categorical and
dimensional aspects of the disorders) to understand what
kind of illness is present and to what degree?
11.
It seems that psychiatric nosology needs to evolve through
a process called as “epistemic iteration.”[1] Changes would
occur to improve the nosological system with time,
keeping in view the gained scientific knowledge over the
period. However, changes in psychiatric classification are
304
12.
13.
14.
15.
16.
17.
18.
Kendler KS. An historical framework for psychiatric nosology. Psychol Med
2009;39:1935‑41.
Mack AH, Forman L, Brown R, Frances A. A brief history of psychiatric
classification. From the ancients to DSM‑IV. Psychiatr Clin North Am
1994;17:515‑23.
Berrios GE. The history of mental symptoms: Descriptive psychopathology
since the nineteenth century. Cambridge: Cambridge University Press;
1996.
Hippius H, Müller N. The work of Emil Kraepelin and his research group in
München. Eur Arch Psychiatry Clin Neurosci 2008;258 (Suppl 2):3‑11.
WHO. The ICD‑10 classification of mental and behavioural disorders:
Clinical descriptions and diagnostic guidelines. Geneva: World Health
Organization; 1992.
APA. Diagnostic and Statistical Manual of Mental Disorders. 4th ed.
DSM‑IV‑TR. Washington DC: American Psychiatric Publication; 2000.
Kawa S, Giordano J. A brief historicity of the Diagnostic and Statistical
Manual of Mental Disorders: Issues and implications for the future of
psychiatric canon and practice. Philos Ethics Humanit Med 2012;7:2.
Goldberg D. Plato versus Aristotle: Categorical and dimensional models
for common mental disorders. Compr Psychiatry 2000;41:8‑13.
Rettew DC, Lynch AD, Achenbach TM, Dumenci L, Ivanova MY.
Meta‑analyses of agreement between diagnoses made from clinical
evaluations and standardized diagnostic interviews. Int J Methods
Psychiatr Res 2009;18:169‑84.
Kendell RE, Cooper JE, Gourlay AJ, Copeland JR, Sharpe L, Gurland BJ.
Diagnostic criteria of American and British psychiatrists. Arch Gen
Psychiatry 1971;25:123‑30.
Wittchen HU. Critical issues in the evaluation of comorbidity of psychiatric
disorders. Br J Psychiatry Suppl 1996;168 (Suppl):9‑16.
Schuckit MA. Comorbidity between substance use disorders and
psychiatric conditions. Addiction 2006;101 (Suppl):76‑88.
Caron C, Rutter M. Comorbidity in child psychopathology: Concepts, issues
and research strategies. J Child Psychol Psychiatry 1991;32:1063‑80.
Surtees PG, Kendell RE. The hierarchy model of psychiatric
symptomatology: An investigation based on present state examination
ratings. Br J Psychiatry 1979;135:438‑43.
Rutter M. Epidemiological methods to tackle causal questions. Int J
Epidemiol 2009;38:3‑6.
Romera I, Pérez V, Menchón JM, Polavieja P, Gilaberte I. Optimal
cutoff point of the Hamilton Rating Scale for Depression according to
normal levels of social and occupational functioning. Psychiatry Res
2011;186:133‑7.
Maser JD, Norman SB, Zisook S, Everall IP, Stein MB, Schettler PJ,
et al. Psychiatric nosology is ready for a paradigm shift in DSM‑V. Clin
Psychol‑ Sci Pr 2009;16:24‑40.
American Psychiatric Association DSM‑5. Available from: http://www.
dsm5.org/Pages/Default.aspx. [Last accessed on 2012 Nov 08].
Source of Support: Nil, Conflict of Interest: None declared
Indian Journal of Psychiatry 56(3), Jul‑Sep 2014