Diagnostic Cases

Goals & Objectives Highlight Bayesian and Boolean processes used in classic diagnosis Demonstrate use/misuse of tests for screening vs. diagnosis Have fun while learning about some common clinical questions

Seven standards for Tests Spectrum composition age distribution, sex distribution, presenting clinical symptoms and/or disease stage, and eligibility criteria for study subjects. Pertinent subgroups Avoidance of workup bias Avoidance of review bias Precision of results for test accuracy Presentation of indeterminate test results Test reproducibility

From Bandiolier dolier/band26/b26-2.html Out of total= 7 standards recommended Year of article publication

Case #1 Strep Throat

The 9 year old, if he had NO rash, would get most benefit from testing. The teacher is benefited mostly by a positive test. How do you tell a “carrier” state from a disease causing strep?

A Bayes Rule of Thumb: Tests work best when Pretest Probability is 50:50

15/400 individuals= 3.75% disease prevalence

Screening Principles Is the problem serious, and do patients care about it? Is the screening test accurate? Is the “gold standard” comparison reliable? Is the positive predictive value acceptable? Does early detection of the disease improve outcomes? Is screening or treatment benign (i.e. not harmful)? Does screening do more good than harm? In a world of limited resources, is screening cost effective? Absolutely effective compared to natural hx of disease? Relatively effective compared to using resources to find/treat other problems?

Depression Case Chief Complaint Sadie Blue is a 22 year old female. Her chief complaint is “no energy". History of Present Illness She reported: enjoys interaction with opposite sex none of the time | depressed most of the time | feel best in morning some of the time | normal thinking none of the time | full life some of the time | irritable most of the time | decisive none of the time | restless a good part of the time | hopeful none of the time | useful none of the time | crying spells a good part of the time | enjoying activities none of the time. She denied: suicidal ideation some of the time. Past, Family, and Social History Social History Activities for Daily Living History of: normal activities none of the time. Review of Systems Constitutional She reported: eating as much as before some of the time | weight loss a good part of the time | fatigue most of the time. Cardiovascular She denied: palpitations some of the time. Gastrointestinal She reported: constipation a good part of the time. Neurological She reported: dyssomnia most of the time. Self-assessment Scales Title: Zung Depression Scale Description: This 14-item scale for depression is a classic in self-rating scales. William Zung at Duke University published this early scale for patient use in Valued for its brevity, it remains a useful screening tool for depression. Patient Score: 65 - Moderate to Marked Scoring Key and Interpretation: : Normal : Minimal to Mild : Moderate to Marked : Severe to Extreme Reference: Zung, W.W.K.: A self-rating depression scale. Archives of General Psychiatry, 1965; 12:63-70.

What does this mean? Title: Zung Depression Scale Description: This 14-item scale for depression is a classic in self-rating scales. William Zung at Duke University published this early scale for patient use in Valued for its brevity, it remains a useful screening tool for depression. Patient Score: 65 - Moderate to Marked Scoring Key and Interpretation: : Normal : Minimal to Mild : Moderate to Marked : Severe to Extreme Reference: Zung, W.W.K.: A self-rating depression scale. Archives of General Psychiatry, 1965; 12:63-70.

Depression Screening

Mammography & CAD My wife recently had a mammogram. She came home and said, "They asked me if I wanted to pay $25 more to have a computer help read my mammogram. I told them 'No, that's the doctors job!'. Was that the right thing to do?"

Mammography & CAD Radiologist Alone CAD Alone Combined R+CAD

Mammography & CAD

Figure 1. ROC curves and sensitivity and specificity data obtained from the interpretation of 104 mammograms by 10 radiologists. A cluster of microcalcifications was present in all cases; 46 cancers and 58 benign lesions were confirmed at biopsy. The effect of a computer aid was tested; it provided an estimate of the likelihood that microcalcifications were due to a malignancy. Sensitivity and specificity results were based on the radiologists’ recommendations for biopsy or follow-up. The ROC curves were based on the radiologists’ diagnostic confidence.

Summary For uncommon illnesses (screening, like breast cancer) there will be lots of false positives. Apply the test correctly, to the correct population “Clinical judgment” means you figure out which population the patient belongs to, before applying the test (i.e. good pretest probability) Good tools for pretest probability are hard to find: use the ones we have well! Watch out for back end costs- complications and death from testing, anaphylaxis from antibiotics, social stigma from psych diagnoses, etc.

Reference How to Read a Paper: Papers that Report Diagnostic or Screening Tests. BMJ 1997: 315: (August 30). Available on Internet, full text.