CMS100 Lecture Review Notes.docx

CMS100 – LECTURE REVIEW NOTES WEEK 1: DIAGNOSTIC PROCESS Diagnostic Process Information from the patient History-taking High diagnostic value and inexpensive/harmless Symptom: manifestation of disease reported by a patient; subjective Patient-centered interviewing Focus on patients’ ideas...

CMS100 – LECTURE REVIEW NOTES WEEK 1: DIAGNOSTIC PROCESS Diagnostic Process Information from the patient History-taking High diagnostic value and inexpensive/harmless Symptom: manifestation of disease reported by a patient; subjective Patient-centered interviewing Focus on patients’ ideas and feelings about illness and impact on life (fears, expectations) Context matters – personal and emotional context; storytelling is important Consider what might be going on and what information is still needed Illness scripts Illness scripts: patterns and organized mental summary of a clinician’s knowledge of a disease; consistent structure including predisposing conditions, clinical features, mechanism of illness Disease illness scripts: to learn, compare and contrast conditions Patient illness scripts: facilitate differential diagnosis Differential diagnosis Differential diagnosis (DDx): list of conditions that are candidates for explaining patient’s concerns Premature close: failing to consider reasonable alternatives after initial diagnosis is made Probability – how likely different conditions are Prevalence: number of people (total # of cases) in a given time period in a certain population Incidence: new occurrences of a condition in a specific population over a given period Evidence Based on information gathered from patient history, physical exam, testing Likelihood ratio: quantifies the value of evidence; likelihood that a test result is expected in patient with the disorder compared to likelihood that same result would be expected in patient without the disorder Testing thresholds: probability below which the diagnosis is so unlikely it is excluded without further testing Treatment thresholds: probability above which the diagnosis is so likely you would treat the patient without further testing Gather information Physical exams Inspection, auscultation, percussion, and palpation Sign: manifestation of a disease that the clinician perceives (see, hear, feel, etc.); objective Red flag: sign or symptom that stands-out or obvious indicator of abnormalities (may be life-threatening or high amount of risk) Take appropriate action WEEK 2: ILLNESS SCRIPTS Disease illness scripts: representation of a condition in the mind of a practitioner; usually includes epidemiology, time course, clinical presentation, mechanism/pathophysiology Epidemiology Demographics – age, sex, race/ethnicity, socioeconomic status *tend to bring on bias* Risk factors – pre-existing conditions Exposures – travel, occupational, hobbies, sexual, drugs, medications, pets, etc. Time course Duration – hyperacute, acute, subacute, chronic Persistence/pattern – constant (stable, progressive), episodic (intermittent, waxing and waning) Clinical presentation – signs and symptoms (most important) Comparing and contrasting illness scripts Organized around a clinical or lab-based syndrome focusing on relevant differences only Between 2-3 diseases – useful for guide reading and studying Diagnostic process is improved Problem representation Create problem list à process list emphasizing most value evidence à abstract patient’s concerns into medical language à finalize problem representation A concise representation of patient’s concern allows matching with disease illness scripts Problem representation has following components: Epidemiology Time course Clinical presentation Medical history Example: Simple Problem List Processed Problem List Patient Illness Script Once or twice a month For past 6 months Throbbing quality on right side of head Last for 4-12 hours Needs to call in sick; wants to lie down and go to sleep Chronic Intermittent Pulsatile 4-12 hours Unilateral Disabling Epidemiology – young woman Time course – chronic, intermittent, 4-12 hours Syndrome statement – pulsatile, unilateral, disabling Other history - depression WEEK 3: DIFFERENTIAL DIAGNOSIS Differential diagnosis: process by which clinicians consider some possible causes of the patient’s signs and symptoms before making a final diagnosis Obtain information from patient and compare this information to one’s understanding of different conditions to generate multiple hypotheses If not done – can fail to consider options after initial guess Errors First guess is usually wrong Most common conditions not typically the most serious and consequences of missing a serious diagnosis are higher Initial guesses are particularly subject to the availability heuristic Availability heuristic: cognitive bias or mental shortcut that individuals use when making judgments or decisions Recognizing common conditions and recall bias – consider conditions more common and familiar or because provider has recently encountered or read about it Cannot list all possibilities – takes time, can lead to unnecessary testing/diagnostic work-up Things to consider in differential diagnoses: Probability: what is most likely? Prognosis: “must-not-miss” conditions; conditions that are most serious if left unconsidered Pragmatism: what conditions have the best benefit to harm ratio if treated When to start considering: After gathering some information about chief concern – allows for more holistic sense of concern and better comparison to disease illness scripts Steps for differential diagnosis: Create a problem list based on information gathered Create a processes problem list – using scientific language and considering only factors that are important to the diagnosis or potential chief concern Create table with differential diagnoses – considering the epidemiology, timing, syndrome/symptoms and mechanism 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. WEEK 4: PROBABILITY Probability: how likely something is usually on a scale of 0-100%; consider probability for better decision-making in the context of uncertainty Overestimating the probability of diagnosis before and after testing Overestimation consistent with cognitive biases – base rate neglect, anchoring bias and confirmation bias Can result in: Medication overuse and excessive procedures Corrupt shared decision-making with patients; need to understand various outcomes to communicate them (spreading misinformation on probability) Bias: human trait; substitute judgments of representativeness for judgments of actual probability Representativeness: degree to which something is representative of, or similar to, the stereotype An uncommon presentation of a common disease is more likely than a common presentation of a rare disease Need to anchor judgement on a good pretest probability and then question the diagnostics of your evidence Pretest probability: best estimate of a disease probability before you do a test; after doing a test you will have a post-test probability - start with a good reference class Reference classes Best reference class: the set of patients that most closely matches this patient Basic reference class: use the prevalence of a disease in a population Pros: Relatively easy to search for Can specify sub-populations to get a more accurate estimate Cons: May be an underestimate if it’s something that people frequently seek medical attention for Less helpful for acute conditions Specific reference class: studies that give eventual diagnosis in patients presenting with complaints similar to your patient’s Pros: Take presenting symptom into account Considers that people tend to seek medical attention for some conditions more than others Cons: Research is less common (harder to find) Clinical scenario in research may be different from your own For references classes, do not use: Incidence of the population – frequency of disease over a period of time Lifetime prevalence – tends to be overestimate WEEK 5: EVIDENCE Evidence: related to updating the beliefs or probabilities based on new information; reasoning under uncertainty allows the incorporation of prior beliefs to knowledge and updating those beliefs as new evidence becomes available Likelihood ratio: a number representing the diagnostic usefulness of a test; used to determine how well a test can discriminate between individuals with a particular condition and those without it Equation: Probability that you would see some evidence if your hypothesis were true/probability that you would see the exact same evidence if your hypothesis was false Numerator and denominator are both probabilities Range from 0 to infinity (can never be a negative number LR = 1 – useless LR > 1 – increases probability (higher the better) LR < 1 – decreases probability (lower the better) LR+ finding was present; does not necessarily increase probability Amount of evidence that you would apply if the finding were present LR- finding was absent; does not necessarily decrease probability (often does) Amount of evidence that you would apply if the finding was absent Likelihood ratios can be based on individual findings, number of individual findings, scores off a questionnaire, etc. Need to make sure no double-counting happens – applying multiple LR’s can become challenging Some findings are closely correlated or even included in other findings Avoid using more than one of the correlated findings otherwise you will be left with an extreme probability estimate If unable to find LR’s in literature, you can calculate them from sensitivity and specificity Sensitivity: in patients who have the disease, the probability that the test will be positive; probability that you would see certain evidence if your hypothesis was true Specificity: in patients who do not have the disease, the probability that your test will be negative; complement probability that you would see the same evidence if your hypothesis were false LR+ = 1−Specificity/Sensitivity​ LR− = Specificity/1−Sensitivity​ Applying Evidence Intuitive – the more certain you are initially, the harder it should be to change your mind Unintuitive – the more uncertain you initially are, the less evidence you need For moderate pretest probabilities: Can increase your pretest probability by a certain % based on the LR For low pretest probabilities: Can multiply the probability by the LR to get an estimate Ex. pretest probability of 2% with an LR of 5 applied results in a post-test probability of about 10% Heckerling Clinical Decision Rule Clinical decision rule used in medicine to help clinicians assess the likelihood of a patient having a certain condition For a certain conditions, can be given a value of scores that list the LR and the post-test probability if pretest probability is a certain number Ex. If a patient came in with 1 of the characteristics for pneumonia, the LR would be 0.2 according to the table. If the patient was in primary care, you would multiply 0.2 x 5 = 1. Therefore 1 would be the post-test probability. If the patient was in the emergency department, you would multiply 0.2 x 15 = 3. PPV and NPV Positive predictive value (PPV): probability that disease is present given that a test was positive Negative predictive value (NPV): probability that disease is absent given that a test was negative Using PPV and NPV assumes that your patient’s pretest probability is the same as those in the study that determined the PPV/NPV As if LR calculation has been done but assumed a pretest probability Simpler but not as accurate as applying LRs Pathognomonic: pathognomonic findings are findings that if present, strongly increases the probability of a condition High LR+ Not necessarily particularly sensitive but highly specific Sine qua non findings: findings which if absent, strongly decreases the probability of a condition Low LR- (close to 0) Evidence: The Process in Practice Steps: Recognize need for more evidence Choose a test – question, physical exam, lab test Perform the test correctly Interpret the results correctly Repeat steps 1-4 until you cross a threshold Errors in practice can include: Fail to recognize the need for more evidence (premature closure) Poorly chosen or missed test (question, physical exam, lab, etc.) Incorrectly performed test Incorrect interpretation (ex. lack of knowledge, bias)