INTRODUCTION TO DIAGNOSIS/ PHYSICAL EXAMINATION
John Gazewood, MD, MSPH
January 9, 2007
Objectives:
• To learn how physicians make a diagnosis
• To understand diagnosis through hypotheticodeductive reasoning
• To understand differential diagnosis
What it is: Using clinical data (history, examination, tests) to infer a suspected
disease or disorder (diagnosis), or a prognosis, for conditions where exact diagnosis not immediately possible (fever in infant).
Three Definitions
Disease or Target Disorder:
Anatomic, biochemical, physiologic or psychologic derangement.
Illness
Symptoms (manifestations perceived by patient) and signs (manifestations perceived by physician) that occur as a result of the disease or target disorder.
Symptoms (and even signs) may be culturally determined.
The Predicament
Social, psychological and economic circumstances in which patient lives.
Diagnosis moves from Illness (symptoms and signs) to disease or target disorder
Patient’s ability to adhere to diagnostic and therapeutic recommendations, and ability to cope with illness, may be profoundly dependent on their predicame
Diagnostic Strategies
I. Pattern Recognition
Immediate recognition that patient’s presentation conforms to a previously learned pattern of disease.
Usually visual, but could also be auditory, based on odor, (even taste), or touch.
Strengths
Based on experience and knowledge
Rapid
Weaknesses
Not easy to teach or explain
May close door too soon
Not useful if you aren’t an expert
II. Exhaustion
The “complete history and physical.”
Thorough, complete search for all of the data, followed by sifting through data for the diagnosis.
Create the database first, then ask the question.
Frequently used by novices (and a variant in POM). Rarely used by experienced clinicians.
Inefficient
III. Diagnostic Algorithims
Progression of diagnostic process down a one of a large number of present paths.
Useful for triage for uncommon conditions, and when delegating responsibility for initial evaluation (eg, to nurses)
IV. Hypothetico-deductive Strategy
A. Hypothesis Generation
Starts immediately with age, gender and chief complaint
B. Where do you get hypotheses?
Knowledge of conditions causing symptoms
Probabilities/disease prevalence
Causal reasoning – knowledge of anatomy, physiology
Heuristics – cognitive shortcuts
Representativenessheuristic – similar to pattern recognition
what is probability that this patient’s features match those of patients with the most likely diagnosis being considered.
Pitfall: consider two diagnoses as equally likely, even though one is probably much more likely
Availability heuristic
based on judgements made on basis of how easily prior similar cases can be brought to mind.
Pitfall: Rare catastrophes more easily remembered, and recent experience also easier to remember
.
C. Hypothesis Testing
Continues during interview, physical exam and tests
New diagnoses come to mind as new data appear
Clinicians keep 5-7 diagnoses in their minds
Look for data to:
confirm a diagnosis (fit the picture) or
rule out the diagnosis (make it less likely or very unlikely)
Common pitfalls in hypothesis testing:
Lack of knowledge
Not thinking of a diagnosis (and proceeding down another road)
Mis-estimating probability (rare diseases, bad treatable diseases)
Result of hypothesis testing: a short list of possible diagnoses in
approximate order of likelihood, based on what you know so far.
Backtracking is fine. “I just thought of one more question.”
C. Hypothesis confirmation
Deciding on your working diagnosis: rarely certain,
but good enough to act on
Ideally, it is: adequate: accounts for your abnormal and normal findings
coherent: fits physiologic/anatomic theory
parsimonious: the simplest diagnosis that explains everything
V. Systematic generation of hypotheses/ differential diagnosis
Why differential diagnosis?
1. You need some diagnoses in your back pocket in case option 1 is wrong.
2. Protects you from failing to consider something important.
How: Mentally go through categories of illnesses: for example
Congenital/ Genetic
Environmental
Endocrine
Infectious
Immunologic
Neoplastic
Psychiatric
Traumatic
Vascular
Differential Diagnosis: A list of three or more diagnoses, in decreasing order of
likelihood, with evidence supporting each (and often evidence against each)
Summary
• Pattern Recognition
• Generate a hypothesis
• Test and revise during history and examination
• Systematically consider other diagnoses
• Arrive at working diagnosis and differential diagnosis
• Confirm
PHYSICAL EXAMINATION
Tools for diagnosis:
• History (75-80%)
• Physical examination (10%)
• Tests (10-15%)
Tools for physical examination:
• your eyes and ears
• your hands (preferably warm)
• stethoscope
• others (high- and low-tech)
Physical examination web modules