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Toward the end of the 19th century, the classifications of psychiatric disorders were rooted in the disciplines of neurology, neuropathology, and psychopathology. Psychodynamic theory focused interest on psychological rather than on brain–behavior relationships and confounded this tradition. When psychoanalysis was considered sufficient therapy for all forms of psychiatric disorder regardless of pathology, the need for diagnostic precision was eliminated. This lack of interest in diagnosis was challenged by the somatic therapies as physicians needed more precise guidelines for the selection of individual treatments for their patients. The acknowledged need for greater diagnostic precision that would be helpful in selecting treatments led to the 1980 DSM-III classification scheme. Initially based on Kraepelinian formulations, the scheme was modified by socio-political needs, rather than experimental evidence (1). Repeated attempts to improve the DSM still leaves the criteria inadequate for selecting treatments and prognosis. The need for a new formulation is implicitly acknowledged in the call for another iteration of the DSM classification (2, 3).

The medical diagnostic model, based on the clinical delineation of symptoms and signs supported by specific laboratory tests, is an alternative. The response to specific treatments is considered verification.

The experience with neurosyphilis is the classical example. Infected patients exhibited mixtures of psychosis, mania, depression, delirium, and neurological signs that were not readily distinguishable from those of dementia praecox and manic-depressive illness. Identification of the spirochete as a causal agent and serum and cerebrospinal fluid diagnostic tests constituted verifying tests, separating the infected patients from those with psychoses because of other causes. The limited success of fever therapies and arsenicals supported the diagnosis, but the rapid and effective relief with penicillin now offers the best validation.

The American Psychiatric Association classifications of 1952 (4) and 1968 (5) identified categories by brief clinical descriptions that evolved from clinical lore. In 1970, members of the Washington University Department of Psychiatry suggested that applying the medical model for diagnosis better delineated clinical syndromes (6). Sixteen syndromes had sufficient supporting data to warrant inclusion in this classification (7). Many DSM-I and DSM-II diagnoses were excluded as unreliable and without validity.

The draft DSM-III classification was based on the Washington University formulations (8). The selection and delineation of categories were atheoretical, but designed to be useful for treatment selection. Final publication under the imprimatur of the American Psychiatric Association, however, required approval by its Board of Trustees. The initial reviews led to angry complaints by constituents that diagnoses generated by psychoanalytic theory, such as ‘neurotic depression’, and supporting psychological therapies had been omitted. Threats to abort the project unless the modifications were accepted led to the inclusion of all diagnoses that had a vocal constituency, resulting in the published stew of imprecise biological, neurological, and psychological classes. The same limitations influenced the upgrades of DSM-IIIR (9), DSM-IV (10), and DSM-IV-TR (11).

Problematic examples abound. Syndromes defined as homogeneous, such as major depression and dysthymic disorder, are clearly heterogeneous. Obsessive–compulsive disorder (OCD) and Gilles de la Tourette’s syndrome, conditions that are better classified together, are separated. Conduct disorder and trichotillomania, conditions that are better separated, are grouped together. Catatonia is linked to schizophrenia despite the evidence that it is more often associated with mood disorders and toxic states, warranting its own category (12, 13). Syndromes like schizophreniform disorder (14) that have no clear validity are included, while frontal lobe syndromes that have supporting validation are not (15). Personality disorders are presented as illness categories despite the evidence that personality is a dimensional construct in behavior and that deviant personality is typically without evidence of brain pathology (16).

Diagnoses are defined by symptom checklists and multiple-choice algorithms occasionally modified by symptom duration. Validation by laboratory tests and by treatment response is rejected (8). DSM formulations sacrifice diagnostic validity to achieve consensus. In the three revisions, the basic rules were unchanged with numerous items added as encouraged by new constituencies (9–11). The alignment with ICD-10 and its brief descriptive paragraph approach added little specificity (17).

Many authors recognize the problem in classification. Speaking as President of the World Psychiatric Association, Juan Mezzich urges a ‘person centered integrative diagnostic model and guide’, a focus that is consistent with psychodynamic philosophy (18). Alas, such a formulation encourages a continuation of the present imprecision in diagnosis.

Is there a better diagnostic model?

Medical model in present DSM classification

  1. Top of page
  2. Medical model in present DSM classification
  3. Specific diagnoses based on the medical model
  4. Problem DSM diagnoses
  5. Other potential diagnoses based on the medical model
  6. References

The medical model for diagnosis made by patterns of symptoms, course of illness, and clinical signs is ascribed to John Hunter. It was in this tradition that Robins and Guze offered the medical model for psychiatric illnesses (6). Some present DSM classes, such as delirium, dementia, the epilepsies, toxic chemical states, and forms of mental retardation, meet the criteria for the medical model.

Delirium is defined by motor disturbance, altered arousal, and diffuse cognitive impairment of acute onset (10). Cognitive assessment and EEG recordings measure brain dysfunction. Blood and urine tests for abnormalities in metabolism and toxic substances identify specific causes. Treatment algorithms to normalize metabolic abnormalities, remove toxins, and sedation are widely accepted.

Dementia is identified by behavioral, cognitive, and laboratory assessments (10). Although effective treatments are lacking, delineating fronto-temporal dementia from Alzheimer’s by cognitive tests and brain imaging defines samples of reasonable homogeneity to encourage research in prevention and treatment.

Guidelines for the epilepsies, toxic chemical states, and mental retardation are based on behavioral criteria verified by neurophysiologic and tissue chemical tests (10). In each instance, a syndrome is defined by psychopathology and verified by laboratory tests resulting in more effective treatment algorithms.

Specific diagnoses based on the medical model

  1. Top of page
  2. Medical model in present DSM classification
  3. Specific diagnoses based on the medical model
  4. Problem DSM diagnoses
  5. Other potential diagnoses based on the medical model
  6. References

Two syndromes that are well supported by the medical model are catatonia (12, 13, 19) and melancholia (20–22).

Catatonia is presently linked in the DSM as a subtype of schizophrenia, with lip service to other options (10). The ICD offers catatonia only as a form of schizophrenia (14). Recent texts, however, identify catatonia by the sustained presence of its classic motor and behavioral features, confirmed with catatonia rating scales (12, 13). The diagnosis is verified by the rapid and immediate relief with i.v. lorazepam (or other sedative anticonvulsant), a test labeled the ‘lorazepam challenge’. It is validated by a rapid treatment response to either high-dose benzodiazepines or to ECT (12, 19). These treatments are highly effective, relieving almost all patients with the syndrome.

Such categorization identifies catatonia in 7–15% of acutely ill psychiatric populations (12). It is most often seen among patients with mood disorder (depression and mania), toxic states (as neuroleptic malignant syndrome), and childhood autistic spectrum disorders (23). The identification of catatonia offers effective treatment options that are not included in common algorithms. We have recommended that catatonia be included as a separate entity in the next psychiatric classification, akin to delirium (13).

Melancholia also lends itself to definition as an independent entity in the classification. It is presented in the DSM as a modifying term in the ‘major depressive disorder’ category. Pregnancy-related depression and abnormal bereavement are identified as independent entities (10). The criteria for major depression, however, do not delineate homogenous samples, and pregnancy and bereavement-related depressions are not distinguishable illnesses. The distinction between manic-depression and other mood disorders assumes that the depression of unipolar disorder differs from the depression of bipolar disorder. This distinction is also roiled by the imprecision of the system, the vague diagnostic criteria for depressive illness, and the avoidance of laboratory tests in syndrome definitions. In contrast, recent reviews identify melancholia as a principal mood disorder among patients identified by the major depression criteria (20–22).

Melancholia is defined as an episode of persistent unremitting mood of apprehension and gloom that compromises normal daily activities. Psychomotor disturbances, as agitation, pacing, wringing hands, or stupor, withdrawal, and limited motor movement, are essential characteristics. Vegetative signs of insomnia, anorexia and weight loss, memory loss, hypotension, and abnormal heart rates are commonplace (20–22).

The diagnosis is verified by abnormal cortisol metabolism or sleep EEG abnormalities. It is validated by the rapid response to ECT, and the response to tricyclic antidepressants and lithium in preference to newer agents (20). Melancholia encompasses examples from the several DSM classes of depression and bipolar disorder and includes patients with or without psychosis. This image of melancholia is consistent with centuries of observation and its recent demarcation as a motor and mood disorder.

Problem DSM diagnoses

  1. Top of page
  2. Medical model in present DSM classification
  3. Specific diagnoses based on the medical model
  4. Problem DSM diagnoses
  5. Other potential diagnoses based on the medical model
  6. References

The present separation disregards the many overlaps in the life courses of patients in these classes. Among bipolar patients, 80% or more experience melancholic depressive episodes that are indistinguishable from those placed in the recurrent major depression category. Nearly 20% of melancholic patients experience manic and hypomanic episodes and many exhibit manic-like symptoms during depression, being identified as ‘mixed’ disorders. Patients in both groups exhibit cortisol abnormalities and both respond to ECT (20).

Psychosis is a common feature. When psychotic depression was recognized as a depressive illness that failed to respond to tricyclic antidepressants (but did respond to ECT), the DSM favored identifying these patients by the specifier of ‘psychotic’, and not creating a separate class (24). Our present understanding finds psychotic depressed patients to meet criteria for melancholia, both in their verification by neuroendocrine abnormalities and by the rapid and effective treatment response to ECT (20).

The criteria for schizophrenia, schizoaffective disorder, and psychotic forms of bipolar disorder are overlapping (14). They lack verifying diagnostic procedures, and are not validated by effective treatments. Whether an instance of psychosis is accompanied by mood disorder, warranting its identification as psychotic depression or bipolar disorder with psychosis or schizoaffective disorder is not distinguishable by the criteria. Nor is it clear that we can identify a singular ‘psychosis’ as suggested by the interest in ‘schizophrenia’.

The separation of the mood disorders into ‘melancholia’ and ‘non-melancholic mood disorders’ offers the best way to identify severely ill mood disorder patients for effective treatment (20, 21).

Other potential diagnoses based on the medical model

  1. Top of page
  2. Medical model in present DSM classification
  3. Specific diagnoses based on the medical model
  4. Problem DSM diagnoses
  5. Other potential diagnoses based on the medical model
  6. References

Syndrome identification by psychopathology, verification by laboratory measures, and validation by treatment response may also be used to develop other homogeneous diagnostic classes. Atypical depression is identified by depressed mood associated with hypersomnia, weight gain, and leaden paralysis. They do not exhibit abnormalities in cortisol metabolism (separating them from melancholic patients). Monoamine oxidase inhibitors (MAOI) medications are reported to be effective when other antidepressants fail (25).

Attention deficit disorder, OCD, and related conditions now classified elsewhere (e.g. trichotillomania, anorexia nervosa, Gilles de la Tourette’s syndrome), panic disorder, and dissociative disorders are other syndromes that lend themselves to better classification by definable psychopathology (e.g. classic OCD and Tourette’s syndrome have many over-lapping features), verified by laboratory testing (e.g. the lactate infusion test for panic disorder, EEG for attention deficit disorder), and validated by treatment response (e.g. response to stimulants in attention-deficit disorder).

To conclude, while several conditions delineated in the present DSM are consistent with the medical model, many are not. Those diagnoses that do not meet this standard should not be established in the classification system. The separation of major depression and bipolar disorder without distinguishing melancholia, the notion of a continuum of brief/schizophreniform/schizophrenia, most forms of personality disorder, and gender-related diagnoses are examples of syndromes that are too imprecise to warrant specific designation. They should be excluded until research offers verifying and validating criteria. The ‘not otherwise specified’ category is the defensive effort to maintain diagnostic class reliability but offers no validity, and should be discarded. Until evidence for such conditions are identified, these terms are best not included in a psychiatric nosology.

Proponents of specific formulations to support unique diagnostic categories should be required to offer identifiable criteria of psychopathology and tests for verification. These diagnoses are best considered ‘provisional’ with a numerical designation that clearly identifies their problematic and experimental nature, awaiting verification by objective tests and validation by specific effective treatments.

The medical model applied rigorously to psychiatric classification delineates validated syndromes, their best treatments, and the best opportunity to define unique pathophysiologies. The identification of the human genome and the possibility that many psychiatric disorders result from genetic faults, for example, offer optimism that diagnosis may ultimately be based on genetic testing, as it now is for Huntington’s chorea. Many researchers believe that the syndromes now labeled schizophrenia, bipolar disorder, and major depressive disorder have concealed within their heterogenic composition a homogeneous subset with unique genetic bases. But, the present diagnostic criteria do not identify homogeneous samples to support such sophisticated testing. The medical diagnostic model delineates more precise groupings. Its application as the basis for the next classification iteration and as the basis for sophisticated research is both clinically and scientifically justified.

References

  1. Top of page
  2. Medical model in present DSM classification
  3. Specific diagnoses based on the medical model
  4. Problem DSM diagnoses
  5. Other potential diagnoses based on the medical model
  6. References
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