TLDR;
This video explains diagnostic frameworks and differential diagnosis in medicine, using a case study of a patient with acute shortness of breath. It covers how to use diagnostic frameworks to list potential causes of a symptom, how to identify key features in a patient's presentation to narrow down the possibilities, and how to create a differential diagnosis, which is a prioritized list of the most likely diagnoses for a specific patient. The video also highlights the iterative nature of the diagnostic process, where new information leads to revisions in the differential diagnosis.
- Diagnostic frameworks are comprehensive lists of potential diagnoses for a symptom, organized by organ system or physiological mechanism.
- Key features are elements of a patient's presentation that help distinguish between diagnostic possibilities.
- Differential diagnosis is a prioritized list of diagnoses that could explain a patient's presentation, based on available information.
Introduction: Diagnostic Frameworks and Differential Diagnosis [0:05]
The video introduces the concepts of diagnostic frameworks and differential diagnosis using a patient case of a man presenting with acute shortness of breath. The initial lack of information about the patient's history and symptoms makes it impossible to pinpoint a specific diagnosis. However, recalling the diseases and conditions that can generally cause shortness of breath is possible. This knowledge will guide the questions to ask the patient, utilizing a diagnostic framework.
Diagnostic Frameworks Explained [1:17]
A diagnostic framework, or schema, is a categorized list of potential causes for a symptom, physical finding, or lab abnormality. These frameworks are commonly organized by organ system, anatomic region, or physiologic mechanism. For acute dyspnea (shortness of breath), a framework can categorize causes into pulmonary, cardiovascular, and miscellaneous systems. Pulmonary causes include pneumothorax, pleural effusion, COPD or asthma exacerbation, mucous plug, pneumonia, aspiration pneumonitis, inhalational injury, interstitial lung disease, and pulmonary embolism. Cardiovascular causes include pericarditis, pericardial effusion, myocarditis, acute decompensated heart failure, endocarditis, acute valve rupture, bradyarrhythmias, tachyarrhythmias, acute coronary syndrome, and hypertensive emergency. Miscellaneous causes include acute anemia, neuromuscular disease, renal failure, metabolic acidosis, upper airway obstruction, and anxiety.
Organizing Diagnostic Frameworks [4:33]
Diagnostic frameworks can be further categorized by subdividing major systems into functional components. For the pulmonary system, these components include the pleura, airways, alveoli, interstitium, and vessels. Similarly, the cardiovascular system can be divided into the pericardium, myocardium, valves, conduction system, and vessels. There isn't one correct way to construct diagnostic frameworks; an alternative approach is to categorize by physiologic mechanisms, such as hypoxemia, hypercapnia, acidemia, poor oxygen delivery, mechanical loading of the respiratory system, and psychiatric causes. The best framework is the one that is most logical and easy to remember for the individual clinician.
Patient Case: Initial Presentation [6:36]
A 42-year-old man with a history of diabetes and hypertension presents to the ER with dyspnea for 30 minutes. Two days prior, he experienced an abrupt onset of dyspnea while watching television, which resolved spontaneously after five minutes. Today, while walking with his wife, the dyspnea recurred and did not resolve. He reports no recent cough, weight changes, or sick contacts. His medications include lisinopril, amlodipine, and insulin. He works as a restaurant manager, has rare alcohol use, and no smoking history.
Key Features in Diagnosis [8:06]
Key features are elements of a patient's presentation that help distinguish one diagnostic possibility from another. In this case, key features include the patient's age, history of diabetes and hypertension, the abrupt onset and episodic nature of the dyspnea, and the absence of chest pain or sick contacts. These features can be organized by asking "who is the patient?" (42-year-old man with diabetes and hypertension, rare alcohol use, nonsmoker) and "what is the disease?" (abrupt onset of dyspnea, two discrete episodes, no associated symptoms).
Differential Diagnosis: Initial Assessment [10:36]
A differential diagnosis is a list of diagnoses that could reasonably explain a patient's presentation, ordered by estimated probability. Considering the episodic nature of the dyspnea, diagnoses that do not typically cause episodic dyspnea can be eliminated from the diagnostic framework. This leaves COPD and asthma exacerbations, mucus plugging, arrhythmias, acute coronary syndrome (ACS), and anxiety disorders. Based on the patient's characteristics, COPD and mucus plugging are less likely. The initial differential diagnosis includes: tachyarrhythmia, ACS, panic attack, bradyarrhythmia, and asthma exacerbation.
Comparing Diagnostic Frameworks and Differential Diagnoses [14:46]
A diagnostic framework is symptom-specific and comprehensive, organized by organ system or physiologic mechanism, and static over time. A differential diagnosis is patient-specific and focused, listed in descending order of probability, and iterative, updated with new data.
Patient Case: Physical Exam and Revised Differential [15:59]
The physical exam reveals a middle-aged man in moderate respiratory distress, with a pulse of 160, blood pressure of 96/70, respiratory rate of 26, and oxygen saturation of 95% on room air. Moderate symmetric crackles are present at both lung bases, the tachycardia is regular with hyperdynamic heart sounds, JVP is moderately elevated, and pulses are weak. This new information leads to a revised differential diagnosis. Asthma and bradyarrhythmia are ruled out. The likely diagnosis is tachyrhythmia, but ACS cannot be completely ruled out until an ECG and troponin levels are obtained. Tachyarrhythmia itself requires further differentiation (e.g., atrial flutter, AV nodal tachycardia, ventricular tachycardia).
Terminology and Key Takeaways [18:08]
In common usage, both diagnostic frameworks and differential diagnoses are referred to as "differential diagnosis," which can be confusing. A key feature is an element of a patient's presentation that helps distinguish diagnostic possibilities. A diagnostic framework is a comprehensive list of diagnoses for a symptom, sign, or lab finding, organized by organ system or physiologic mechanism. A differential diagnosis is a list of diagnoses that could plausibly explain a specific patient's presentation, ordered by estimated probability.
