hello I'm Eric strong from Stanford University and the paloalto VA hospital this is a three-part video series entitled a guide to clinical reasoning or how to create an accurate differential diagnosis from a patient's presentation the learning objectives of the this video are first to demonstrate a standardized approach to generating a focused differential diagnosis from a patient's presentation second to create concise problem representations using semantic qualifiers and clinical syndromes next to understand the types of Frameworks to which the key features of a presentation should be applied and finally to know the categories of diagnosis which should be included in the differential unfortunately literature and textbooks that discuss and attempt to teach clinical reasoning often fail because of dense terminology and a focus on abstract Concepts that trainees find difficult to apply at the bedside with concrete examples in this video I'll be presenting an approach to clinical reasoning focusing on the differential diagnosis that is practical at the bedside accessible to students and other novice providers and minimizes unfamiliar terminology part one will introduce the clinical reasoning process and parts two and three will go through examples start to finish of how to apply that process to a real world patient part two will be an example at the level of a preclinical student and part three will be an example at the level of an intern I'm going to start by defining the term clinical reasoning clinical reasoning is the process by which a health care provider takes objective data acquired from an actual patient and interprets it using factual Knowledge from a textbook or the medical literature in order to either make a diagnosis or develop a treatment plan it isn't a single individual skill but rather a collection of related skills it involves interpretation of subjective data evaluation of the accuracy and validity of data synthesis of individual pieces of data into higher order groups determination of the relevance of scientific literature for a specific clinical situation critical evaluation of the arguments for and against diagnosis application of biostatistics and finally integration of different types of knowledge into a complete decision-making process although clinical reasoning isn't just about figuring out a diagnosis that will be the focus of this particular set of videos I consider there to be five steps to generating a differential diagnosis the first is to acquire data and to do this I recommend that you use all available sources that includes first and foremost the interview and examination of the patient but also diagnostic tests and chart review focusing on the medication list recent Primary Care notes and recent discharge summaries also depending on the circumstances you may consider talking to close family members and friends for collateral information provided of course that the patient cons sense as you gain experience with clinical reasoning you may begin to find yourself skipping the five-step process and actually start developing differential diagnosis as you are talking to and examining the patient that is as you are acquiring the data this skill dramatically helps with efficiency and helps choose the most appropriate diagnostic tests however it does not necessarily result in a more accurate diagnosis in the end as it sets one up for something called anchoring bias anchoring bias is a tendency to place too much weight on a single piece of information acquired early in the data acquisition process and a failure to update the differential diagnosis when conflicting information is later presented for example if a patient's uh HPI or history of present illness focuses on his shortness of breath and he happens to mention early on that it's worse when lying down a specific symptom called orthopnea that may lead a clinician to begin hypothesizing during the interview that the patient has heart failure additional investigation May then be appropriately directed towards confirming or refuting this hypothesis if the clinician then learns the patient has a fever has a focal decrease in breath sounds on exam and a consolidation on chest x-ray he or she should reconsider their original hypothesis if leici fails to reconsider the initial leading diagnosis of heart failure even after acquiring much data suggesting a different diagnosis in this case pneumonia he or she has committed anchoring bias so here's the bottom line for efficiency sake it's a good idea to consider the differential diagnosis in real time during the patient hmp but be aware of anchoring bias and once the entire data set is collected force yourself to return to the beginning of the clinical reasoning process so that each piece of data and element of the presentation is given its appropriate weight once you've acquired the data the next step is to identify the key features key features are the individual elements of the presentation which are likely to help differentiate one diagnosis from another for example in a patient with episodic chest pain whether or not the pain comes on with exercise will help to determine the likelihood it is from cardiac esia therefore this is a key feature in contrast the sever of chest pain on a 1 to 10 scale is surprisingly nonpredictive of the eventual diagnosis and thus I would generally not consider its severity to be a key feature key features include both positive and negative findings they may be from History exam Labs other tests or chart review the third step is to create a problem representation this should use semantic qualifiers and should synthesize with related findings into clinical syndromes some of these terms may be unfamiliar to you so let me explain what do I mean by the term problem representation this is a one to two sentence summary using precise medical terminology of the most highly relevant aspects of the patient's History exam and diagnostic tests sometimes problem representation is used synonymously with the terms summary statement as well as impression the latter term commonly used in written notes in the United States semantic qualifiers are qualitative abstractions of the symptom of a case in which an opposing abstraction is either explicit or implied they help to reframe a patient's symptom into terms more familiar to the clinician and easier to communicate to others common categories of qualifiers include the onset of symptom for example was it abrupt or Progressive and acute or chronic has the course of the symptom been continuous or episodic is the site unilateral or bilateral proximal or distal diffuse or localized what do the symptom trigger postprandial or exertional or ptic or positional and is the symptom associated with pain or is it painless the use of semantic qualifiers when reframing a patient symptom is thought to Aid in accessing chunks of information stored in the clinician's memory and is associated with a higher likelihood of arriving at the correct diagnosis let's look at some examples of how to use semantic qualifiers to reframe symptoms imagine a patient in the ER States for the last 30 minutes my chest is hurt whenever I take a deep breath we would reframe this as acute ptic chest pain or another patient states over the past several months both legs have been getting weaker and weaker this becomes chronic progressive bilateral lower extremity weakness a word of caution here some information is lost when the patient's presentation is translated into semantic qualifiers which can set one up for bias if the original history is never Revisited now what about that phrase synthesize into clinical syndromes a short elaboration on this is that a concept stellation of clearly related findings should be grouped together into a single clinical syndrome if possible for example if a patient has confusion a fever to 39° heart rate of 120 beats per minute blood pressure of 130 over 60 respiratory rate 24 white blood cell count 16,000 creatinine of 2.4 and positive blood cultures you can synthesize that as severe sepsis and if another patient has jaund sies confusion asterixis a total bity of 25 and an INR of two that can be summarized as hepatic failure another word of caution don't mistake the clinical syndrome for the diagnosis for example it's great if you recognize a patient has severe sepsis however severe sepsis is not a final diagnosis and your diagnostic reasoning should not end here you must also determine what has caused the severe sepsis is it community acquired pneumonia or urinary tract infection or appendicitis so now using semantic qualifiers and clinical syndromes how do we construct the problem representation there are at least two approaches to this the one I favor is to link four categories of information into a single sentence using a standardized order age and gender first then highly relevant past medical history followed by the primary symptom using semantic qualifiers and ending with the highly relevant diagnostic data using clinical syndromes when possible for example a 60-year-old woman with a history of poorly controlled diabetes presents with chronic progressive exertional dpia with exam and chest x-ray findings of volume overload and with unremarkable routine labs and EKG the other approach to the problem representation is to consider only this category so for this patient the problem representation becomes just chronic progressive exertional dpia I personally don't like this approach as much because I think the upside to being more concise is outweighed by the downside of eliminating the additional information but you certainly will come across the second approach from time to time all right so let's get back to our five steps that was a long one uh step four is to adopt a framework to better understand the patient problem this framework may be anatomic physiologic or some other type and it's commonly adapted from a reference source Frameworks typically take the form of a categorized General differential diagnosis where the strategy for categorization depends upon the specific problem what are some types of Frameworks a framework for acute renal failure May first divide diagnosis up into pre-renal intrarenal and post renol meaning is the problem before blood gets to the kidney inside the kidney or after urine leaves the kidney some of these categories can be further subdivided so pre-renal ideologies can either be from dehydration or from low cardiac output and intrarenal ideologies can either be glomular tubular or interstitial another example of a framework this time for anemia divides the ideologies into hypoproliferative and hyp proliferative hypoproliferative anemias can be from nutritional deficiencies bone marrow failure kidney disease or chronic disease Andor inflammation hyper proliferative anemia can be from acute blood loss or homolysis there is not just one acceptable framework for a specific patient problem for example let's consider the patient we just mentioned a minute ago a 60-year-old woman with a history of poorly controlled diabetes who presents with chronic progressive exertional dpia with examined chest x-ray findings of volume overload and with unremarkable routine labs and EKG what type of framework might we choose to adopt here in my experience the most likely framework a clinician would choose for this problem is an anatomic one also referred to as organ based so for this woman with dpia that means that it could be a cardiac problem a pulmonary problem or a heem problem as as we just saw briefly with the kidneys all of our organs can be further subdivided into functional components so a problem in the heart could be in The myocardium coronary vessels valves conduction system or paric cardium a problem in the lungs can be located in the Airways alvioli pulmonary vessels interstitium or plora and finally hematologic issues can involve any of the individual cell lines or coagulation problems or issues with paraproteins however with dnia as a chief complaint the major hematologic concern is of course anemia my thrownness with these Frameworks is limited by the minimum font size I want to use uh in in the uh diagrams here but if I was being more thorough I would also list the renal system here with subcategories for the renal arteries guli tubules interstitium and collecting system so that's the anatomic framework which is just one way of categorizing the differential diagnosis for this problem another completely acceptable framework that's based more on physiology might ask what are the pathophysiologic mechanisms that can trigger dpia there is hypoxia which can be from VQ mismatch impaired diffusion or shunt there is hypercapnea which can be from obstructive lung disease Central hypoventilation neuromuscular disease or decreased respiratory compliance less commonly is dpia from acidemia either from pathologic Acid production or from poor acid elimination finally input from the cerebral cortex from anxiety and pain can also lead to the subjective sensation of dnia this framework isn't necessarily better or worse than the anatomic one just different it's likely that some people will naturally gravitate towards one and some to the other one other type of framework that I feel both obligated and reluctant to mention is the pneumonic framework I feel obligated because many medical schools still teach and expect their students to use it I am reluctant because I think it is vastly inferior to other types of Frameworks but nevertheless here it is one such pneumonic that's taught is vindicate the v stands for vascular the I for inflammatory the N for neoplastic D is degenerative the second I is idiopathic C is congenital a is autoimmune t for traumatic and lastly e for endocrine okay one more step to go apply the key features to the framework which will generate the preliminary differential diagnosis when applying the key features the clinicians should use their presence or absence to estimate the likelihood of the diseases or pathophysiologic states that are suggested by the framework as a brief example imagine a 55-year-old man with a history of alcoholism and depression presents with chronic progressive bilateral lower extremity edema with an exam notable for anasara and a serum albumin of 1.5 G per deciliter one of the several Frameworks one might employ for this case might be a physiologic one where there are four categories for the four major mechanisms of hypo albuminemia there is impaired intake of protein seen in malnutrition impaired utilization and synthesis of protein seen in liver disease excessive glomular filtration of protein seen in the nephrotic syndrome and excessive GI loss of protein a syndrome known as protein losing enteropathy the key features for such a patient might include a history of depression how does Depression affect the probability of any of the categories in the framework it's not linked to liver disease independent of substance abuse and it's not associated with either Fric syndrome or protein losing enteropathy however it does increase the chance of malnutrition as a patient may not be eating properly in his depressed state if key features also included the presence of spider angom and splenomegaly on exam that would dramatically increase the likelihood of liver disease if the patient has no history of GI symptoms particularly diarrhea that would dramatically decrease the probability of protein losing uropathy as all pathologies that cause this General diagnosis also lead to diarrhea and a host of other symptoms and if the key features included a UA without any protura that would be definitive enough evidence as to completely Ru out nephrotic syndrome from the differential altogether estimating to what degree individual key features impact which components of the framework Andor differential is a skill that requires both textbook knowledge familiarity with scientific literature and experience in my opinion it is the single aspect of clinical reasoning that more than any other differentiates novice clinicians from the experts perhaps I should have started this video with a discussion of the next issue but although most of you are likely familiar with the term differential diagnosis let me Define it specifically so that we are all on the same page with how I'm using it a differential diagnosis often abbreviated as just the differential is a list of possible diagnoses which may explain the patient presentation it should include those diagnosis in which either its likelihood is high enough or the danger if it should be missed is high enough in order to Warrant additional testing to investigate that specific diagnosis it may or may not include additional diagnoses whose likelihood is low enough to not warrant immediate testing but which have not been completely ruled out the differential diagnosis should be prioritized in descending order of likelihood a solid Focus differential diagnosis should include the following the one diagnosis that you believe to be the most likely this is known as the working diagnosis or provisional diagnosis two to four diagnoses that are very common in general for which this patient's case could be either a typical or an atypical presentation any diagnoses which are rapidly fatal if untreated of which this patient's case could plausibly be the result this is often known as a quote don't miss diagnosis finally any diagnoses which are specifically suggested by standout features of the patient's history including unusual Hobbies or job and recent travel to an exotic location most of these unusual standout features will be what we refer to as red herrings a red herring is an unusual element of the presentation that falsely appears quite relevant But ultimately distracts the clinician away from the true diag nois it seems common for medical trainees to be instructed to keep their differential diagnosis broad what this is meant to mean is that the trainee should not prematurely jump to conclusions regarding the culprit organ system or determine that a single diagnosis is the only one worth considering unfortunately the recommendation to keep the differential broad is frequently misunderstood to mean that the differential should be very long and span every organ system in the body a long differential is more more problematic than a focused one even in training because it actually displays less thought and it can be difficult to formulate a diagnostic plan if there are 15 different conditions simultaneously under consideration for the typical Internal Medicine admission I would consider four to six diagnoses a good ballpark range to aim for When developing a practical differential my last words of caution first the framework and differential diagnosis are not the same thing the framework may be adopted directly from a reference source and is not specific for your patient the differential diagnosis on the otherand includes only those diagnoses relevant to the patient in question a differential diagnosis that has not been made specific to the patient is nearly worthless when prioritizing the differential and establishing the provisional diagnosis in general an atypical presentation of a common disease is more likely than a typical presentation of a rare disease finally the true typical presentation of a disease does not always match the textbook description of a disease or its historically taught presentation for example it's usually taught in medical schools and reinforced in suboptimally researched textbooks that spontaneous bacterial peritonitis or SBP usually presents with abdominal pain abdominal tenderness and so-called parital signs on physical exam in reality the most common presentation of SBP in a patient with known liver disease is altered mental status with or without a fever and without any abdominal signs at all as another example it's frequently believed that patients with pericardial tanod either usually or always present with hypotension in reality when studied it's been shown that the majority of patients with proven tanod are actually not hypotensive at presentation there are many many more examples of discrepancies between how an inaccurate classic presentation of a disease negatively impacts diagnostic reasoning most patients with heart attacks don't have crushing substernal chest pain most patients with migraine headaches don't experience a visual Aura before headache onset the list goes on and on so that's it for my five steps to a differential diagnosis once again they are first acquired data second identify the key features third create a problem representation using semantic qualifiers and clinical syndromes fourth adopt the framework and last apply the key features to the framework in order to generate the differential diagnosis that concludes part one of this guide on clinical reasoning focusing on how to create an accurate and focused differential diagnosis as I mentioned at the beginning in Parts 2 and three I'll go through examples from start to finish of how how to apply this approach to a real world patient as you listen to Parts two and three I'd consider pausing intermittently as you go in order to practice working through the case on your own la