L 20 Clinical Reasoning and Medical Decision Making — Study Notes

Learning Objectives

  • Define clinical reasoning and medical-decision making.
  • Describe components of the clinical reasoning process.
  • Understand dual-process theory (System 1 and System 2 thinking) and its implications for clinical decision-making.
  • Develop the ability to use illness scripts to facilitate clinical reasoning.
  • Understand the principles behind creating a differential diagnosis, including the need for comprehensive, organized reasoning to ensure important conditions are not missed.
  • List the components of the VINDICATE and SPIT differential diagnosis mnemonic.
  • Identify common cognitive biases that can impact clinical decision-making and diagnostic accuracy.
  • Develop strategies for recognizing and mitigating biases that can impact medical-decision making.
  • Synthesize the principles of clinical reasoning, differential diagnosis, and cognitive bias to make effective, evidence-based clinical decisions.

Clinical Reasoning: Definition and Scope

  • The mental process of gathering, analyzing, and synthesizing information to make medical decisions.
  • Can be a difficult concept to explain, teach, and replicate.
  • Components involve the Clinical Problem or Presenting Patient and what goes on in the provider’s head, leading to the Outcome (Diagnosis and/or Plan).

Timeframe and Variability in Clinical Reasoning

  • Can occur in seconds to minutes for a classic presentation of a common problem.
  • Can take weeks to months for more complex cases, including literature reviews, consultations with specialists, and seeking opinions of colleagues.

Dynamic Nature and Tenets of Clinical Reasoning

  • Dynamic process that involves:
    • Clinical knowledge
    • Critical thinking
    • Pattern recognition
    • Tenets of evidence-based medicine
  • Goal: Make safe, evidence-based decisions.

Key Questions in Clinical Reasoning (What to Ask/Do)

  • What history questions should I ask?
  • What physical exam techniques should I perform?
  • What labs should I order for this patient?
  • What is the most likely diagnosis for this patient?
  • What life-threatening diagnoses should I consider?
  • Is this patient stable or is this a medical emergency?
  • Do I need to refer this patient to a specialist?

Clinical Reasoning: Impact on Practice

  • Directly impacts patient outcomes.
  • Helps prevent diagnostic errors.
  • Core competency of PA practice.

The Clinical Reasoning Process (Five Steps)

  1. Acquire Data
  2. Interpret and Organize Data
  3. Make hypotheses
  4. Test Hypotheses
  5. Diagnosis and Plan

From Bates' Guide (Chapter 5) – Key Elements

  • Key elements of the clinical diagnostic reasoning process include data gathering, interpretation, hypothesis generation, hypothesis testing, and formulation of the diagnosis and plan. (Reference: Bates' Guide to Physical Examination and History Taking, 13e, 2021)

Dual Process Theory: Overview

  • A cognitive framework describing two different types of thinking used in medical decisions and diagnoses.

System 1 (Fast, Intuitive)

  • Characteristics: fast, intuitive, pattern recognition, used in familiar situations, relies on illness scripts.

System 2 (Slow, Analytical)

  • Characteristics: slow, analytical, deliberate, more complex, used in unfamiliar situations, hypothesis testing.

How the Two Systems Interact

  • Clinicians usually start with System 1 and move to System 2 as needed.
  • System 1 saves time but is more susceptible to error and bias.
  • System 2 is likely more accurate but slower and more resource-intensive in everyday practice.
  • Experienced clinicians toggle between the two systems.

Illness Script: Definition and Purpose

  • An organized mental summary of a disease a clinician has knowledge of.
  • A structured summary based on experience and knowledge.
  • Develops and evolves over time.
  • Useful for comparing and contrasting disease processes.

Illness Script Components (Format #2)

  • Pathophysiology
  • Epidemiology
  • Clinical Presentation (Signs and Symptoms)
  • Diagnostics
  • Management

Illness Script: Impetigo Formats

  • Format #1: Who? Why? Impetigo? When? What?
  • Format #2: Pathophysiology; Epidemiology; Clinical Presentation (Signs and Symptoms); Diagnostics; Management

Illness Script Example: Community-Acquired Pneumonia

  • Pathophysiology: Infection of the lower respiratory tract.
  • Epidemiology: Older age, structural lung disease.
  • Symptoms/Signs: Fever, cough, dyspnea for days, typically < 1 week.
  • Diagnostics: Leukocytosis, infiltrate on chest X-ray support the diagnosis.
  • Management: Antibiotics.

In-Class Illness Script Exercise (Impetigo)

  • Take ~10 minutes in groups of 3–5 to create two Illness Scripts for Impetigo.

Illness Script: Impetigo Format #1

  • Most commonly occurs in children 2–5 years of age.
  • Spreads easily with close contact.
  • Staph and Strep carriers.
  • Warm, humid conditions.
  • Broken skin—cuts, rash, bug bites.
  • Crowding, poverty, poor hygiene.
  • Carriers of Staph and Strep.
  • Definition: Superficial bacterial infection of the skin.
  • Pathogen: Staph aureus (Most common).
  • Typical progression: Papules to pustules/vesicles then honey-colored crust.
  • Typical distribution: Face and extremities.

Illness Script: Impetigo Format #2

  • Contagious, superficial bacterial infection of the skin, Staph aureus (most common).
  • Age group: 2–5 years.
  • Key lesions: Papules to pustules/vesicles to honey-colored crust (nonbullous).
  • Diagnostics: None or Gram stain of pus/exudate.
  • Treatment: Topical antibiotics (Mupirocin) three times daily; oral antibiotics in some cases.

Illness Script: Basal Cell Carcinoma (BCC) – In-Class Exercise

  • Take 5–10 minutes in groups of 3–5 to create one Illness Script for Basal Cell Carcinoma.

Illness Script: Basal Cell Carcinoma

  • Pathophysiology
  • Epidemiology
  • Clinical Presentation (Signs and Symptoms)
  • Diagnostics
  • Management

Illness Script: In-Class Exercise (BCC) – Activity

  • Create an illness script for Basal Cell Carcinoma.

Differential Diagnosis: Concepts and Principles

  • Differential diagnosis is a method of analysis that distinguishes a disease or condition from others with similar clinical features.
  • Clinicians must consider: likelihood, severity, and treatability of each potential diagnosis.
  • The process is dynamic and changes as new information is gathered.
  • Your differential before entering the room will change as you gather information via history and/or physical exam.

Can’t Miss Diagnoses

  • Providers must always consider a “can’t miss” diagnosis.
  • May require diagnostic testing to confirm absence of these conditions.
  • Sample discussions: Chest pain, Dyspnea, Back pain.

Chest Pain Differential (Sample Differential)

  • GERD (heartburn/acid reflux) or other GI issues
  • Costochondritis or other musculoskeletal issues
  • Anxiety or panic attacks
  • Respiratory infections (influenza, COVID-19, pneumonia)
  • Pneumothorax
  • Pericarditis
  • Pulmonary embolism
  • Acute coronary syndrome
  • Aortic dissection

Dermatology: Can’t Miss Dermatologic Conditions

  • Melanoma
  • Necrotizing Soft Tissue Infections (NSTI)
  • Stevens-Johnson Syndrome (SJS)
  • Toxic Epidermal Necrolysis (TEN)

Rash Case – Can’t Miss Diagnosis Example (SJS risk assessment)

  • A 41-year-old female with a rash starting 1 day ago: what history questions help assess likelihood of SJS?

SJS/TEN Features

  • Medication use
  • Prodrome: fever, malaise, myalgias, sore throat, conjunctivitis, flu-like symptoms
  • Mucosal involvement: oral cavity, nose, ear, genitals
  • Ocular symptoms

Skin Lesion – Can’t Miss Diagnosis Example (Melanoma)

  • A 55-year-old patient with a spot on the leg: what history questions help assess likelihood of melanoma?

Melanoma Risk Factors (Key Risks)

  • New or changing lesion
  • Change in size, shape, color
  • Bleeding
  • Personal or family history of skin cancer
  • Excessive sun exposure, tanning bed use, history of sunburns

Differential Diagnosis Tools: VINDICATE

  • VINDICATE categories:
    • V: Vascular
    • I: Infectious
    • N: Neoplastic
    • D: Degenerative
    • I: Iatrogenic
    • C: Congenital
    • A: Autoimmune
    • T: Traumatic
    • E: Endocrine

VINDICATE Examples (Selected)

  • Rash examples:
    • V: Petechia, purpura
    • I: Impetigo, viral exanthem, tinea
    • N: Kaposi sarcoma
    • D: NA
    • I: Drug eruption/reaction
    • C: Slate-gray nevi
    • A: Lupus rash, psoriasis
    • T: Abrasions, contact irritants
    • E: Acanthosis nigricans

VINDICATE – Chest Pain Example

  • V: Acute coronary syndrome
  • I: Myocarditis
  • N: Lung cancer
  • D: Aortic stenosis
  • I: Aortic dissection (post-cardiac instrumentation)
  • C: Coarctation of the aorta
  • A: Eosinophilic esophagitis
  • T: Rib fracture
  • E: Thyrotoxicosis

SPLIT: Differential Diagnosis (Skin Lesion)

  • Serious (must not miss)
  • Probable (most likely)
  • Interesting (rare/zebra)
  • Treatable (clinically actionable)

SPLIT Case: Skin Lesion

  • S: Melanoma
  • P: Seborrheic keratosis
  • I: Trichofolliculoma
  • T: Basal cell carcinoma

Justified Differential Diagnosis: What Justifies the List

  • Information elicited that supports the diseases included in the differential
  • Patient characteristics (age, gender, etc.)
  • History findings (pertinent positives and negatives)
  • Physical examination findings (pertinent positives and negatives)
  • Laboratory and diagnostic testing results
  • Justification leads to prioritization of differential diagnoses

SHARP (Short Answer, Rationale Provision) – Item Format

  • SHARP is a format used to assess clinical reasoning where the short-answer response to the most likely diagnosis is presented alongside the patient’s medical record.
  • Learner selects the information from the record that best supports their decision; gray boxes in the example show the selected information.
  • Abbreviations shown include BMI, BP, HEENT, HPV, Ht, O2 sat, RA, resp, etc.

Justified Differential Diagnosis: Application (SCFE Example)

  • A 12-year-old male with a limp: in groups, create a differential diagnosis (5 items).
  • Example output includes SCFE (slipped capital femoral epiphysis) as a key consideration.

Cognitive Biases in Medical Decision Making

  • Definition: Cognitive biases are systematic errors in thinking that affect decisions and judgments.
  • Many biases arise from overreliance on System 1 thinking.
  • Biases are normal, predictable, and manageable.

Common Cognitive Biases

  • Anchoring
  • Availability bias
  • Confirmation bias
  • Premature closure
  • Overconfidence bias
  • Omission bias
  • Commission bias
  • Framing effect
  • Outcome bias

Anchoring Bias (Definition and Example)

  • Relying too heavily on an initial piece of clinical information.
  • Example: A past medical history of panic disorder leads to missed acute coronary syndrome.

Availability Bias (Definition and Example)

  • Judging probability based on recent experience.
  • Example: Over diagnosing pulmonary embolism after a recent case.

Confirmation Bias (Definition and Example)

  • Seeking data that supports a preconceived diagnosis; ignoring conflicting evidence.

Premature Closure (Definition and Example)

  • Stopping diagnostic thinking too early before all evidence is gathered/verified.

Overconfidence Bias (Definition and Example)

  • Overestimating one's diagnostic accuracy; discounting second opinions or guidelines.

Omission Bias, Commission Bias, Framing Effect, Outcome Bias

  • Omission: Preferring inaction to action; fear of harm from treatment.
  • Commission: Preferring action to inaction; e.g., antibiotics for viral illness “just in case.”
  • Framing: Being swayed by how information is presented regarding risks/benefits.
  • Outcome: Desiring a specific outcome that biases judgment (e.g., diagnosing X to avoid a complication).

Cognitive Bias Examples (Practice Scenarios)

  • Case 1: 41-year-old with chest pain and shortness of breath; anxious with panic attack; ED diagnoses panic attack; Missed Pulmonary Embolism; Bias:
  • Case 2: Febrile child labeled as “virus” without exam/tests; later develops sepsis; Bias:
  • Case 3: 22-year-old with sore throat and tonsillar swelling diagnosed as strep pharyngitis; no further history or testing; risk of missing infectious mononucleosis (splenic rupture); Bias:

Strategies to Mitigate Cognitive Bias

  • Metacognition: “Could I be wrong?” — pause to reflect.
  • Clinical guidelines/Algorithms: Use clinical decision support tools.
  • Second Opinions: Ask a colleague when uncertain.
  • Diagnostic Time-outs: Step back when uncertain or case is atypical.
  • Bias Awareness Training: CME or simulation scenarios.

Complexity and Uncertainty in Medical Practice

  • There is no “answer key” in medicine.
  • Medical knowledge is ever-increasing and evolving.
  • Uncertainty is inevitable in clinical medicine.
  • Quote: “Medicine is a science of uncertainty and an art of probability” — William Osler.
  • Practical guidance:
    • Accept uncertainty as part of the process.
    • Do not focus solely on the right answer; work on decision making and clinical reasoning skills.
    • Medicine involves problem-solving; there may not be one clear answer.
    • Clinicians may say, “Sometimes we just don’t know.”

Development of Clinical Reasoning Skills at MWU

  • OSCEs (Objective Structured Clinical Examinations)
  • Case groups in Clinical Medicine III and IV
  • Online clinical reasoning resources
  • Aquifer (online clinical reasoning cases)

Aquifer Case: 68-year-old with a skin lesion

  • Illustrates an online case used to practice differential diagnosis and reasoning.

References

  • Clinical Reasoning, Assessment, and Plan. In: Bickley LS, Szilagyi PG, Hoffman RM, et al. eds. Bates' Guide to Physical Examination and History Taking, 13e. Lippincott Williams & Wilkins, 2021. Accessed July 08, 2025.
  • Corrao S, Argano C. Rethinking clinical decision-making to improve clinical reasoning. Front Med (Lausanne). 2022;9:900543.
  • OpenAI. ChatGPT (July 29, 2025 version) [large language model]. OpenAI. Accessed July 29, 2025.
  • ten Cate O. Introduction. 2017 Nov 7. In: ten Cate O, Custers EJFM, Durning SJ, editors. Principles and Practice of Case-based Clinical Reasoning Education: A Method for Preclinical Students [Internet]. Cham (CH): Springer; 2018. Chapter 1. Available from: https://www.ncbi.nlm.nih.gov/books/NBK543763/
  • Witt EE, Onorato SE, Schwartzstein RM. Medical students and the drive for a single right answer: teaching complexity and uncertainty. ATS Scholar. 2021;3(1):27-37.