Underdiagnosing and Overdiagnosing Psychiatric Comorbidities: Page 2 of 2
Underdiagnosing and Overdiagnosing Psychiatric Comorbidities: Page 2 of 2
Low intelligence is another commonly overlooked cognitive deficit. The patient who appears to comprehend treatment directives but who declines to ask questions when provided the opportunity and who ultimately fails to follow instructions may have impaired intellectual functioning or a verbal comprehension level that is lower than the instructional level of care providers.
The key to reducing diagnostic errors of commission or omission is to gather as much information as possible before finalizing the diagnosis. Crucial elements include:
• A complete, longitudinal history of presenting problems.
• Use of a structured diagnostic method to facilitate thoroughness of evaluation.
• Collateral information from other health care providers, family members, and friends.
• A review of diagnostic criteria rather than reliance on one’s memory of DSM-IV criteria.
• Assessment of factors that affect diagnostic accuracy.
Kashner and colleagues16 found the Structured Clinical Interview for DSM-IV (SCID) to be more effective than a previous, less-structured protocol in accurately diagnosing conditions in community mental health patients. This tool resulted in a change in diagnosis for 20% of patients in whom it was used; in contrast, a change in diagnosis was made for only 2% of patients in a control group. The SCID also captured more comorbid diagnoses (51% for the SCID group vs 5% for the control group), including substance use disorder, anxiety, and eating disorders.
A summary of commonly used diagnostic tools that might facilitate accurate identification of primary psychiatric disorders and comorbidities follows. While these tools facilitate the diagnostic process, they are used primarily to provide additional information to support diagnoses, to aid evaluations by focusing the attention of providers, and to help the interviewer be more thorough in gathering diagnostic information.
Many professionals have begun to standardize their assessment practices by replacing unstructured, open-ended interviews with more systematic methods of eliciting psychopathological criteria. As a result, they have significantly increased diagnostic accuracy.2,17,18 For example, Miller and colleagues2 compared the efficacy of structured (eg, SCID–Clinical Version, Computer Assisted Diagnostic Interview) and unstructured, traditional diagnostic assessments and found that structured methods were significantly superior.
Others have also demonstrated similar results.1,17,19 Basco and colleagues1 demonstrated the superiority of structured interviews in identifying important psychiatric comorbidities. Compared with unstructured methods used by clinicians in a community mental health setting, the SCID identified more than twice the number of active comorbid Axis I disorders. Unfortunately, structured interviews are time consuming and require some training to administer.
An alternative to structured interviews is Zimmerman’s Psychiatric Diagnostic Screening Questionnaire (PDSQ).20 This 125-item self-report measure screens for 13 adult psychiatric disorders. It was designed to facilitate diagnostic assessment in outpatient mental health and primary care settings by providing clinicians with information on disorders that are most likely to be present. Because it focuses the interviewer’s diagnostic questions on commonly diagnosed disorders, it increases efficiency. The internal consistency of the 13 scales is high, with a mean a coefficient of 0.85.21 Except for the psychosis scale, sensitivity levels range from 85% to 92%. Specificity values range from a low of 50% for generalized anxiety disorder to a high of 89% for bulimia nervosa.22 There are no subscales for mania, hypomania, or dysthymia in the PDSQ.
The reliability of Axis II diagnoses based on a single interview has been problematic. Symptoms of personality disorders can be subtle, and it may take many different interactions with a patient before a clinician can confidently make a diagnosis. Structured interviews are available to help improve the accuracy of Axis II diagnoses by guiding the interviewer in gathering sufficient information; however, they are lengthy and impractical in many clinical settings.
The Personality Disorder Interview-IV is a 2-hour semistructured interview in which an overall dimensional profile is created by rank-ordering possible diagnoses.23 Interview questions are clustered by personality disorder and follow-up questions are provided. Two other examples are the Personality Disorder Examination24 (PDE) and the International PDE25; the latter was developed from the PDE to diagnose disorders in the DSM-IV and the International Classification of Diseases-10.26 Another example is the SCID for Personality Disorders-II, a 120-item self-report questionnaire that is followed by a semistructured interview to examine more closely any criteria that were endorsed.27
The Coolidge Axis II Inventory28 is a Likert-type self-report scale that is also used to assess personality disorders; however, caution should be taken in the interpretation of these scales. Personality traits that are problematic for the patient are not necessarily evidence of a DSM-IV disorder. Patient traits that present a challenge for the clinician may reflect a problem with the therapeutic alliance.
Alcohol and illicit drug use can be problematic, even at subclinical levels. While substance abuse and dependence can be assessed with the Axis I diagnostic tools described previously, a more focused measure is the Alcohol Dependence Scale.29 The scale contains 25 items that measure withdrawal, control, awareness of compulsion to drink, tolerance, and addictive behavior. It can be administered as an interview or can be self-administered by computer, and it takes 5 to 10 minutes to complete. It has shown high internal consistency, with Cronbach’s a values ranging from 0.85 to 0.99. Cutoff scores are determined according to the purpose of treatment and typically range from 3 to 8.29 A lower cutoff score might suggest levels of substance use that could potentially interfere with the primary Axis I problem under treatment.
There is no substitute for being thorough in conducting a diagnostic evaluation. This includes taking the time to gather information from the patient and significant others, going over prior medical records, and/or observing the patient over time and updating the diagnosis if appropriate. Keep in mind the importance of probing for comorbidities, of not jumping to conclusions about their presence when a patient presents with a few striking symptoms, and of the need to interpret symptoms correctly. Clinicians may be forced to draw quick diagnostic conclusions with limited information in busy practice settings or when patients are acutely ill. In these cases, it is important to follow up after patients have been stabilized, to reevaluate diagnoses when patients seem to be nonresponsive to treatment, and to consider the possibility that comorbid problems may be interfering with treatment outcome.
Even when the clinician is familiar with DSM-IV criteria, it is easy to forget the details over time. Most diagnostic tools provide a reminder of symptoms that are common to each category of diagnosis. If it is impractical to use such tools, it is prudent to review DSM-IV criteria when new patients present for treatment. This allows clinicians to recalibrate their assessments, refresh their memories, and reduce drift over time of how diagnoses are derived. By taking time to be thorough in diagnosing primary and comorbid psychiatric disorders, the clinician can facilitate treatment selection and treatment outcome.
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Evidence-Based References Ramirez Basco M, Bostic JQ, Davies D, et al. Methods to improve diagnostic accuracy in a community mental health center. Am J Psychiatry. 2000;157:1599-1605.
Kashner MT, Rush JA, Suris A, et al. Impact of structured clinical interviews on physicians’ practices in community mental health settings. Psychiatr Serv. 2003;54:712-718.