Diagnostic Rating Scales and Psychiatric Instruments

Overview

Unlike other medical specialties, psychiatry relies almost exclusively on patient interviews and on observation for diagnosis and treatment monitoring. With the absence of specific physical or biomarker findings in psychiatry, the mental status examination (MSE) represents our primary diagnostic instrument. The MSE provides a framework to collect the affective, behavioral, and cognitive symptoms of psychiatric disorders. Often, the MSE provides enough detail for psychiatrists to categorize symptom clusters into recognized clinical syndromes, and to initiate appropriate treatment.

However, in some settings, the MSE alone is insufficient to collect a complete inventory of patient symptoms or to yield a unifying diagnosis. For example, if a psychotic patient has symptoms of avolition, flat affect, and social withdrawal, it might be difficult to determine (from the standard diagnostic interview alone) whether this pattern reflects negative symptoms, co-morbid depression, or medication-induced akinesia. At other times, performing an MSE may not be an efficient use of time or resources to achieve the desired clinical goal: imagine how many fewer patients might be identified during depression screening days if the lengthy, full MSE were the screening instrument of choice. Finally, the subjective nature of the MSE often renders it prohibitive in research studies, in which multiple clinicians may be assessing subjects; without the use of an objective, reliable diagnostic tool, subjects may be inadequately or incorrectly categorized, generating results that are difficult to interpret and from which it is difficult to generalize.

By using diagnostic rating scales, clinicians can obtain objective, and sometimes quantifiable, information about a patient's symptoms in settings where the traditional MSE is either inadequate or inappropriate. Rating scales may serve as an adjunct to the diagnostic interview, or as stand-alone measures (as in research or screening milieus). These instruments are as versatile as they are varied, and can be used to aid in symptom assessment, diagnosis, treatment planning, or treatment monitoring. In this chapter, an overview of many of the psychiatric diagnostic rating scales used in clinical care and research is provided ( Table 6-1 ). Information on how to acquire copies of the rating scales discussed in this chapter is available.

General Considerations in the Selection of Diagnostic Rating Scales

How “good” is a given diagnostic rating scale? Will it measure what the clinician wants it to measure, and will it do so consistently? How much time and expense will it require to administer? These questions are important to consider regardless of which diagnostic ratings scale is used, and in what setting. Before describing the various ratings scales in detail, several factors important to evaluating rating scale design and implementation will be considered ( Table 6-2 ).

A first consideration concerns the psychometric measures of reliability and validity. For the psychotic patient mentioned earlier, what would happen if several different physicians watched a videotape of a diagnostic interview, and then independently scored her negative symptoms with a rating scale? The scale would be considered reliable if each of the physicians arrived at a similar rating of her negative symptoms. Reliability refers to the extent that an instrument produces consistent measurements across different raters and testing milieus. In this case, the negative symptom rating scale specifically demonstrates good inter-rater reliability, which occurs when several different observers reach similar conclusions based on the same information.

Recall that for this patient, though, negative symptoms constituted only one possible etiology for her current presentation. If the underlying problem truly reflected a co-morbid depression, and not negative symptoms, a valid negative symptom rating scale would indicate a low score, and a valid depression rating scale would yield a high score. The validity of a rating scale concerns whether it correctly detects the true underlying condition. In this case, the negative symptom scale produced a true negative result, and the depression scale produced a true positive result ( Table 6-3 ). However, if the negative symptom scale had indicated a high score, a type 1 error would have occurred, and the patient may have been incorrectly diagnosed with negative symptoms. Conversely, if the depression scale produced a low score, a type 2 error will have led the clinician to miss the correct diagnosis of depression. The related measures of sensitivity, specificity, positive predictive value, and negative predictive value (defined in Table 6-2 and illustrated in Table 6-3 ) can provide estimates of a diagnostic rating scale's validity, especially in comparison to “gold standard” tests.

Several important logistical factors also come into play when evaluating the usefulness of a diagnostic test. Certain rating scales are freely available, whereas others may be obtained only from the author or publisher at a cost. Briefer instruments require less time to administer, which can be essential if large numbers of patients must be screened, but they may be less sensitive or specific than longer instruments and lead to more diagnostic errors. Some rating scales may be self-administered by the patient, reducing the possibility of observer bias; however, such ratings can be compromised in patients with significant behavioral or cognitive impairments. Alternatively, clinician-administered rating scales tend to be more valid and reliable than self-rated scales, but they also tend to require more time and, in some cases, specialized training for the rater. A final consideration is the cultural context of the patient (and the rater): culture-specific conceptions of psychiatric illness can profoundly influence the report and interpretation of specific symptoms and the assignment of a diagnosis. The relative importance of these factors depends on the specific clinical or research milieu, and each factor must be carefully weighed to guide the selection of an optimal rating instrument.

General Diagnostic Instruments

Suppose that a research study will evaluate brain differences between individuals with an anxiety disorder and healthy subjects. Anxiety is highly co-morbid with a number of psychiatric conditions, which if present among subjects in the anxiety group might confound the study results. At the same time, assurance that the “healthy” subjects are indeed free of anxiety (or of other psychiatric illnesses) would also be critical to the design of such an experiment. The use of general psychiatric diagnostic instruments, described in this section, can provide a standardized measure of psychopathology across diagnostic categories. These instruments are frequently used in research studies to assess baseline mental health and to ensure the clinical homogeneity of both patient and healthy control subjects.

One of the most frequently used general instruments is the Structured Clinical Interview for DSM-IV Axis I Diagnosis (SCID-I). The SCID-I is a lengthy, semistructured survey of psychiatric illness across multiple domains ( Box 6-1 ). An introductory segment uses open-ended questions to assess demographics, as well as medical, psychiatric, and medication use histories. The subsequent modules ask specific questions about diagnostic criteria, taken from the DSM-IV, in nine different realms of psychopathology. Within these modules, responses are generally rated as “present,” “absent (or subthreshold),” or “inadequate information”; scores are tallied to determine likely diagnoses. The SCID-I can take several hours to administer, although, in some instances, raters use only portions of the SCID that relate to clinical or research areas of interest. An abbreviated version, the SCID-CV (Clinical Version), includes simplified modules and assesses the most common clinical diagnoses.

While the SCID-I is generally considered user-friendly, its length precludes its routine clinical use. An alternative general rating instrument is the Mini-International Neuropsychiatric Interview (MINI), another semi-structured interview based on DSM-IV criteria. Questions tend to be more limited with this test than with the SCID-I, and are answered in “yes/no” format; however, unlike the SCID-I, the MINI includes a module on antisocial personality disorder and has questions that focus on suicidality. Because the overall content of the MINI is more limited than the SCID-I, the MINI requires much less time to administer (15 to 30 minutes).

A third general interview, the Schedules for Clinical Assessment in Neuropsychiatry (SCAN), focuses less directly on DSM-IV categories and provides a broader assessment of psychosocial function ( Box 6-2 ). The SCAN evolved from the older Present State Examination, which covers several categories of psychopathology, but also includes sections for collateral history, developmental issues, personality disorders, and social impairment. However, like the SCID-I, the SCAN can be time consuming, and administration requires familiarity with its format. While the SCAN provides a more complete history in certain respects, it does not lend itself to making a DSM-IV diagnosis in as linear a fashion as does the SCID-I and the MINI.

Two additional general diagnostic scales may be used to track changes in global function over time and in response to treatment. Both are clinician-rated and require only a few moments to complete. The Global Assessment of Functioning Scale (GAF) consists of a 100-point single-item rating scale that is included in Axis V of the DSM-IV diagnosis ( Table 6-4 ). Higher scores indicate better overall psychosocial function. Ratings can be made for current function and for highest function in the past year. The Clinical Global Impressions Scale (CGI) consists of two scores, one for severity of illness (CGI-S), and the other for degree of improvement following treatment (CGI-I). For the CGI-S, scores range from 1 (normal) to 7 (severe illness); for the CGI-I, they range from 1 (very much improved) to 7 (very much worse). A related score, the CGI Efficacy Index, reflects a composite index of both the therapeutic and adverse effects of treatment. Here, scores range from 0 (marked improvement and no side effects) to 4 (unchanged or worse and side effects outweigh therapeutic effects).

General diagnostic instruments survey a broad overview of psychopathology across many domains. They can be useful as screening tools for both patients and research subjects, and in some cases can determine whether individuals meet DSM-IV criteria for major psychiatric disorders. However, they do not provide the opportunity for detailed investigations of affective, behavioral, or cognitive symptoms, and often do not provide diagnostic clarification for individuals with atypical or complex presentations. Diagnostic rating scales that focus on specific domains (such as mood, psychotic, or anxiety symptoms) can be of greater value in these situations, as well as in research efforts that focus on symptom-specific areas. In the following sections, rating scales that are tailored to explore specific clusters of psychiatric illness and related medication side effects will be discussed.

Scales for Mood Disorders

The diagnosis and treatment of mood disorders present unique challenges to the psychiatrist. The cardinal features of major depressive disorder can mimic any number of other distinct neuropsychiatric illnesses, including (but not limited to) dysthymia, anxiety, bipolar-spectrum disorders, substance abuse, personality disorders, dementia, and movement disorders. In some cases, overt depressive symptoms precede the tell-tale presentation (e.g., mania) for these other disorders, and more subtle signs and symptoms of the root disorder are easily missed in standard diagnostic interviews. Moreover, because most antidepressant medications and psychotherapies take effect gradually, daily or even weekly progress can be difficult to gauge subjectively. Diagnostic rating scales can be invaluable in the clarification of the diagnosis of mood disorders and the objective measurement of incremental progress during treatment.

The Hamilton Rating Scale for Depression (HAM-D) is a clinician-administered instrument that is widely used in both clinical and research settings. Its questions focus on the severity of symptoms in the preceding week; as such, the HAM-D is a useful tool for tracking patient progress after the initiation of treatment. The scale exists in several versions, ranging from 6 to 31 items; longer versions include questions about atypical depression symptoms, psychotic symptoms, somatic symptoms, and symptoms associated with obsessive-compulsive disorder (OCD). Patient answers are scored by the rater from 0 to 2 or 0 to 4 and are tallied to obtain an overall score. Scoring for the 17-item HAM-D-17, frequently used in research studies, is summarized in Table 6-5 . A decrease of 50% or more in the HAM-D score suggests a positive response to treatment. While the HAM-D is considered reliable and valid, important caveats include the necessity of training raters and the lack of inclusion of certain post-DSM-III criteria (such as anhedonia).

The Montgomery-Asberg Depression Rating Scale (MADRS), another clinician-administered instrument, also measures depressive severity, and correlates well with the HAM-D. The MADRS contains 10 items, each reflecting symptom severity from 0 to 6, with a maximum possible total score of 60. The MADRS generally covers similar symptoms to the HAM-D-17, but may be more sensitive to antidepressant-related changes than the HAM-D Scale. It is not so well suited for assessing atypical depression, since it does not examine increased appetite or sleep (see Table 6-6 ).

The most frequently used self-administered depression rating scale is the Beck Depression Inventory (BDI). The BDI is a 21-item scale in which patients must rate their symptoms on a scale from 0 to 3; the total score is tallied and interpreted by the clinician ( Table 6-7 ). Like the HAM-D, the BDI may be used as a repeated measure to follow progress during a treatment trial. Although easy to administer, the BDI tends to focus more on cognitive symptoms of depression, and it excludes atypical symptoms (such as weight gain and hypersomnia). An alternative rating scale, the Inventory of Depressive Symptomatology (IDS), provides more thorough coverage of atypical depression and symptoms of dysthymia. The IDS is available in both clinician-rated (IDS-C) and self-administered (IDS-SR) versions, and it contains 28 or 30 items. Suggested interpretation guidelines are given in Table 6-8 .

The Quick Inventory of Depressive Symptomatology-Self-Report (QIDS-SR) is a 16-item self-rated instrument derived from the IDS, for measuring self-reported changes in symptom severity during antidepressant clinical trials. Each question is rated on a scale of 0 to 3 and the total score is obtained by summing the scores on most of the individual items, and summing the highest scores of 3 categories (sleep, appetite/weight, and psychomotor activity). The highest possible total score is 27. (See Table 6-9 .)

Two other self-administered scales, the Zung Self-Rating Depression Scale (Zung SDS) and the Harvard Department of Psychiatry National Depression Screening Day Scale (HANDS), are frequently employed in primary care and other screening sessions due to their simplicity and ease of use. The Zung SDS contains 20 items, with 10 items keyed positively and 10 keyed negatively; subjects score each item as present from 1 or “a little of the time” to 4 or “most of the time.” To obtain the total score, positively-keyed items are reversed and then all of the items are summed ( Table 6-10 ). The HANDS includes 10 questions about depression symptoms, and it is scored based on the experience of symptoms from 0 or “none of the time” to 3 or “all of the time” ( Table 6-11 ). Although the Zung SDS and HANDS take only a few minutes to administer, they are less sensitive to change than are the HAM-D and the BDI; like these other scales, the Zung SDS lacks coverage for atypical symptoms of depression.

There are fewer validated rating scales to assess manic symptoms than there are for depression. However, two clinician-administered scales, the Manic State Rating Scale (MSRS) and the Young Mania Rating Scale (Y-MRS), have both been used extensively on inpatient units to characterize the severity of manic symptoms; the Y-MRS also correlates well with length of hospital stay. The MSRS contains 26 items and is rated on a 0 to 5 scale, based on the frequency and intensity of symptoms. Particular weight is given to symptoms related to elation-grandiosity and paranoia-destructiveness. The Y-MRS consists of 11 items and is scored following a clinical interview. Four items are given extra emphasis and are scored on a 0 to 8 scale (irritability, speech, thought content, and aggressive behavior); the remaining items are scored on a 0 to 4 scale. Each of these scales may be used to detect symptoms of mania in patients with undiagnosed bipolar disorder, although their reliability to do so has not yet been formally tested.

Scales for Psychotic Disorders

Psychotic symptoms vary widely in their presentation, from the most florid (e.g., hallucinations and delusions) to the most inert (e.g., social withdrawal and catatonia). During interviews with thought-disordered patients, it can be quite a demanding task to cover the spectrum of psychotic symptoms—not only because of their sheer heterogeneity but also because they can be extremely difficult to elicit in impaired or uncooperative individuals. Moreover, antipsychotic medications can predispose patients to movement disorders that are elusive to diagnose; for example, the overlap between negative symptoms and neuroleptic-induced akinesia can be difficult to disentangle during the diagnostic interview. Several diagnostic rating scales have been developed to aid clinicians in categorizing and monitoring psychotic symptoms, as well as movement disorders. Each psychotic symptom scale is administered by a clinician.

The Positive and Negative Syndrome Scale (PANSS) is a 30-item instrument that emphasizes three clusters of symptoms: positive symptoms (e.g., hallucinations, delusions, disorganization), negative symptoms (e.g., apathy, blunted affect, social withdrawal), and general psychopathology (which includes a variety of symptoms, e.g., somatic concerns, anxiety, impulse dyscontrol, psychomotor retardation, mannerisms, posturing). Separate scores are tallied for each of these clusters, and a total PANSS score is calculated by adding the scores of the three subscales. Each item is rated on a scale from 1 (least severe) to 7 (most severe) following a semi-structured interview (the Structured Clinical Interview for Positive and Negative Syndrome Scale, SCI-PANSS). Normative data for the PANSS subscales, taken from a sample of 240 adult patients who met DSM-III criteria for schizophrenia, are given in Table 6-12 . Designed to organize data from a broad range of psychopathology, the PANSS provides an ideal scale for monitoring baseline symptoms and response to antipsychotic medications. However, it can take 30 to 40 minutes to administer and score the PANSS, and examiners must have familiarity with each of the PANSS items.

Several additional instruments are available to assess global psychopathology and positive and negative symptom severity in psychotic patients. The 18-item Brief Psychiatric Rating Scale (BPRS) evaluates a range of positive and negative symptoms, as well as other categories (such as depressive mood, mannerisms and posturing, hostility, and tension). Each item is rated on a 7-point scale following a clinical interview. The BPRS has been used to assess psychotic symptoms in patients with both primary psychotic disorders and secondary psychoses, such as depression with psychotic symptoms. More detailed inventories of positive and negative symptoms are possible with the 30-item Scale for the Assessment of Positive Symptoms (SAPS) ( Table 6-13 ) and the 20-item Scale for the Assessment of Negative Symptoms (SANS) ( Table 6-14 ). For each of these instruments, items are rated on a scale of 0 to 5 following a semi-structured clinical interview, such as the Comprehensive Assessment of Symptoms and History (CASH). Correlations between SAPS and SANS scores with their counterpart subscales in the PANSS are quite high. Recently, it has been argued that the SANS demonstrates higher validity if attention scores are removed.

An additional consideration in evaluating negative symptoms is whether they occur as a primary component of the disorder, or as a consequence of co-morbid processes, such as depression, drug effects, or positive symptoms. The Schedule for the Deficit Syndrome (SDS) uses four criteria to establish whether negative symptoms are present, enduring, and unrelated to secondary causes ( Box 6-3 ). Each of the four criteria must be satisfied for a patient to qualify for the deficit syndrome, as defined by Carpenter and colleagues.