03. Differential Diagnosis-2.pdf

Differential Diagnosis Foundations of Clinical Medicine CMS100 Objectives 1. 2. 3. 4. Understand the value of differential diagnosis Understand the steps in the differential diagnosis process Understand some common errors in differential diagnosis Create differential diagnoses for patient cases Diff...

Differential Diagnosis Foundations of Clinical Medicine CMS100 Objectives 1. 2. 3. 4. Understand the value of differential diagnosis Understand the steps in the differential diagnosis process Understand some common errors in differential diagnosis Create differential diagnoses for patient cases Differential Diagnosis The process by which clinicians consider some possible causes of the patient’s signs and symptoms before making a final diagnosis After obtaining some information from the patient, compare this information to one’s understanding of different conditions to generate multiple hypotheses about what might be going on If not done deliberately, people tend to fail to consider options after arriving at an initial guess This would involve considering that you might have been wrong Errors Why not just go with your first guess? Especially for beginners, this is wrong too often The most common conditions are not typically the most serious and the consequences of missing a serious diagnosis are higher (also see testing thresholds lecture) Initial guesses are particularly subject to the availability heuristic I.e. Tendency to use information that comes to mind quickly and easily Favors recent or more memorable experiences Errors Why not just make a list of all possibilities? Aka “possibilism” Technically impossible Takes a long time and tends to be a confusingly long list without the extra possibilities adding value Can lead to unnecessary testing/diagnostic work-up People sometimes use mnemonics as frameworks for generating differentials (e.g. “VINDICATE”) but even these tend to lead to excessively long lists Ultimately, you can add differentials later anyway if they become more reasonable to consider A Different Approach Consider: Probability: what is most likely? Prognosis: “must-not-miss” conditions – which conditions are worst if left unconsidered Pragmatism: what conditions have the best benefit:harm ratio if treated We will consider a framework later that takes these factors into account without explicitly naming them (see thresholds lectures) When to Start Considering Generally done after gathering a bit of information about the chief concern If you start too early, the list will tend to be pointlessly long Will let you work with a more holistic sense of the patient’s concern Will allow you to better compare it with your disease illness scripts You will update this list later as more information becomes available Resources Some textbooks and websites will provide long lists of differentials E.g. Isabel ddxof Example A 45-year-old man has a history of headaches Example A 45-year-old man tells his naturopathic doctor about his 10-year history of occasional headaches which tend to occur predominantly on the right side of his head. He rates the intensity of the pain as grade 5 out of 10 on a scale of 1-10 and finds he is able to continue working during these headaches. They last between 4 to 5 hours. He has no symptoms before the headaches begin. There is no vomiting or light sensitivity. He was diagnosed with diabetes 1 year ago, which is being treated with metformin A physical examination reveals mild weakness (power graded 4/5) and increased reflexes in the right leg. Example Problem List Processed Problem List 45 years old Male 10-year history Occasional Right-sided Pain 5/10 Can continue working Last between 4 to 5 hours No symptoms before the headaches No vomiting No light sensitivity Mild right leg weakness 4/5 Increased reflexes in the right leg Diabetic Taking metformin Middle aged Male Chronic Intermittent 4-5 hrs duration Unilateral Not disabling No prodrome No vomiting No photophobia R leg mild muscle weakness R leg hyperreflexia Diabetes medicated with metformin Example Patient Illness Script Epidemiology 45-year old male Timing Chronic, intermittent, 4-5 hrs duration Syndrome Unilateral, non-disabling headaches without Statement vomiting, photophobia or prodrome. Mild R leg muscle weakness and hyperreflexia. Other history Diabetic, taking metformin Example Epidemiology Timing Syndrome Mechanism Migraine Tension-type headache Brain tumor Common Often start in adolescence F>M Very common Any age M~F Rare Typically later life M~F Recurring, 4-72 hrs duration Recurring Last hours to days or may be unremitting Progressive, constant, worse at night or early morning Bilateral headache Mild-to-moderate intensity Pressing or tightening, Non-pulsating No more than one of photophobia, phonophobia or mild nausea Neurological findings (generalized – e.g. cognitive changes, seizures – and/or focal – e.g. sensory, motor, language) often meet criteria for tension headaches muscular origin; related to increased resting muscle tension Usually metastasis; presses on surrounding brain tissue Unilateral headache Disabling intensity Nausea Photophobia Phonophobia May be preceded by an aura Complex; likely neurogenic Another Example Kim, a 15-year-old girl, has a CC of a very sore throat. She has been sick for 8 days and has had a fever and fatigue. She denies having a cough or stuffy nose. Physical exam reveals an oral temperature (OT) of 38.8°C, a heart rate (HR) of 112 beats per minute (bpm), a blood pressure (BP) of 98/68 mmHg (taken on her left arm while sitting, “LAS”). Her respiratory rate (RR) is 16 breaths per minute and is even and unlabored. On examination of her pharynx, she has bilateral erythematous, enlarged tonsils with a white exudate. There is diffuse cervical (anterior and posterior) and axillary lymphadenopathy. No mouth lesions are noted. On abdominal exam, there is splenomegaly. Another Example Problem List Processed Problem List 15-year-old sore throat 8 days Fever Fatigue No cough no stuffy nose OT: 38.8°C HR: 112 bpm BP: 98/68 mmHg LAS RR: 16 bpm bilateral erythematous, enlarged tonsils with a white exudate diffuse cervical and axillary lymphadenopathy No mouth lesions are noted splenomegaly Teenager Pharyngitis Subacute Febrile No cough Bilateral erythematous, enlarged tonsils with a white exudate No palatal petechiae Diffuse cervical and axillary lymphadenopathy Splenomegaly Another Example Patient Illness Script Epidemiology 15-year-old Timing Subacute Syndrome Pharyngitis and fever with no cough. Bilateral Statement erythematous, enlarged tonsils with a white exudate. No palatal petechiae or ulcers. Diffuse cervical and axillary lymphadenopathy. Splenomegaly Other history n/a Another Case Pharyngitis Epidemiology Timing Syndrome Mechanism Age 5-15 Acute Pharyngitis, fever, absence of cough, pharyngeal and/or tonsillar exudate, anterior cervical lymphadenopathy Infection with Group A betahemolytic strep (GABHS) Age 10-35 Acute to chronic Pharyngitis, fever, cervical lymphadenopathy, fatigue, malaise, tonsillar exudate, palatal petechiae, splenomegaly Infection with Epstein-Barr virus High risk sexual behaviour Acute to subacute Pharyngitis, palatal ulcers, no exudate, maculopapular rash, fever, fatigue, headaches, myalgia, arthralgia, lymphadenopathy, night sweats, GI symptoms Initial, uncontrolled stage of HIV infection GABHS (strep throat) EBV (mononucleosis) Acute Retroviral Syndrome Summary 1. Differential diagnosis allows for the possibility that the initial beliefs about the diagnosis were incorrect, facilitating better decision-making 2. Differential diagnosis is aided by appropriate problem representation (see illness scripts lecture) 3. Beginners may create excessively long or extremely short lists based on misconceptions about medical diagnosis (e.g. “possibilism” and/or insufficient compensation for the availability heuristic)