Differential Diagnosis The cornerstone of Western medicine
Initial thoughts. . . • Each question asked during the patient interview reflects a sign, symptom, or risk factor for a disease that we feel may explain the patient’s presentation. • Differential diagnosis directs our patient encounter from the very beginning.
Where do we begin? • Use available information • Age • Gender • Chief complaint • Vital Signs • Chart Review (as applicable)
Studying is important! • Understanding of epidemiology • Age, gender, race • Knowledge of disease presentation • Which diseases present with cough, which with fever, acute versus chronic symptoms, etc. • Ability to recognize abnormal vital signs • Is the patient hypertensive? Tachycardic? Febrile?
Formal Differential • Not needed: • Classic presentation of common disease • Risk of acute mortality • Needed: • Atypical disease presentation • Examination or testing does not confirm suspected diagnosis • Multiple signs and symptoms with no obvious connection
Occam’s Razor • A principle attributed to the 14th century logistician and Franciscan friar, William of Ockham • “Pluralitas non est ponenda sine neccesitate” • Plurality (numerous ideas) should not be posited (considered) without necessity • That is. . . Keep it SIMPLE!!
Intuitive Postulates • Consider each sign or symptom individually • Generate a separate differential for each of the patient’s issues • Compare the problem-specific differentials • Include diagnoses that appear frequently • Those which explain all pertinent positive findings. • Exclude diagnoses that appear infrequently • Diagnoses that do not explain a majority of findings are unlikely candidates.
How to proceed. . . • Infection, neoplasm, meds/drugs, and exposure are the most likely categories • Neoplasm, trauma, meds/drugs can be ruled-out convincingly by further history alone • Exposure may be difficult – is the patient aware? • DIRECT questioning – specific possibilities
Proceeding. . . • After ranking categories – begin to think about specific diagnoses • In this case – infection is most probable • List out specific infectious etiologies
INFECTION • Infectious Mononucleosis (Epstein Barr - EBV) • Upper respiratory infection (rhinovirus, paramyxovirus, etc.) • Sinusitis • Measles • Varicella • Pneumonia • Bronchitis
Making the diagnosis • Using epidemiological data, history, and physical we attempt to discover the correct diagnosis • If our working diagnosis proves inadequate, we return to the differential and start anew
Streamlined Process • Utilizing this more fluid thought process, as each category is considered, specific diagnoses are postulated simultaneously • As you develop the differential, more than one diagnosis may be plausible • In this case the final differential is comprised of the top possibilities in each of medical category
As illustrated here - • INFECTION • upper respiratory infection, sinusitis, EBV • EXPOSURE • insecticides, petroleum based chemicals or fumes • MEDICATION/DRUGS • inhalant abuse, medication overdose (aspirin)
Epidemiology • The study of disease in a specific population • Disease prevalence varies tremendously in different patient populations • Students should become familiar with age, gender, and race-related disease risk • In clinical study, understanding disease-specific epidemiology is equally important to knowledge of diagnosis and treatment
Epidemiology is essential • Sinusitis remains the most probable diagnosis in lieu of any further information • Young child who had not received standard immunizations consider other infectious etiologies such as varicella or measles, along with sinusitis • If this same young child had a history of exposure to someone with either of these illnesses, consideration of these diagnoses would be moved ahead of sinusitis altogether
Epidemiology is essential • Furthermore, the likelihood of pulmonary malignancy in a child would be infinitesimally small • 16-year-old male who had recently spent numerous sleepless nights studying for final examinations, we would strongly consider EBV infection • A 65 year old male with a life-long history of construction work involving asbestos, then asbestosis or pulmonary malignancy might be considered before sinusitis or EBV
Developing a Thorough Differential • First review categories or areas of medicine • Once you had identified categories that are plausible, then proceed to specific diagnoses within those categories • This ensures that you consider ALL possible areas of medicine and do not just focus on the most common
VINDICATES • Vascular • Infectious, Inflammatory • Neoplastic • Drugs • Iatrogenic, Idiopathic/psychogenic • Congenital • Autoimmune (allergic) • Trauma • Endocrine (metabolic/nutrition), Exposure • Systems
Rank-listing the differential • Ranking of differential makes the list of diagnoses more useful • Assuming that the diagnoses considered adequately explain the patient’s symptoms, the final order is based on two concepts – • Most common/most likely diagnosis • Diseases that are associated with high mortality or morbidity
Move uncommon disorders higher? • The diagnosis is plausible in our patient • Nearly impossible in our patient? Not necessary to consider it from the outset – regardless of lethality. • The diagnosis can be eliminated by additional history, physical examination, or non-invasive testing • Diagnosis requires invasive study, specialized laboratory eval. or expensive testing? It should remain toward the bottom of our differential list • The diagnosis is associated with acute mortality • Diagnosis is associated with mortality only after a prolonged period of time? Consideration following further evaluation of more common disorders is advisable
Sample case: Adolescent patient with chest pain • Common causes include pleurisy, costochondritis, benign overuse myalgia, or anxiety/stress • As such, these diagnoses should appear at the top of the differential – with specific historical and physical data influencing the final order • Myocardial infarction (MI), while plausible, would be highly unlikely in an otherwise healthy child • Therefore, MI would be placed lower on the list of possible etiologies
Myocardial infarction? • Using the criteria outlined above, eliminating the possibility of MI prior to final diagnosis is a reasonable approach • The diagnosis is plausible, is associatedwith acute mortality, and can be ruled-out with a minimally invasive test Electrocardiogram • Enzymes (CKMB/Troponin) are rarely needed in this scenario
Teaching Points • If the patient’s presentation is consistent with a rare diagnosis, then further evaluation by whatever means necessary is compulsory • The point is not to limit our evaluation in order to save money or time – instead, diagnostic evaluation should be driven by clinical indication • What is emphasized herein is that you must THINKthrough the process of deciding which diagnoses are considered first, and which can wait.
The doctor as an artist • Each disease process does not present in exactly the same way every time. Medicine is more than pure scientific study – it is an art form • One cannot simply memorize key facts about a diagnosis and limit consideration of this disease to the fulfillment of all necessary criteria alone • An astute physician recognizes the possibility of disease presenting atypically – thereby not explaining every sign or symptom
Test of time. . . • Having made a final diagnosis, continued observation of the patient will allow us to determine if our suspicion was correct • Students should recognize that uncovering the etiology of disease may require time • Early on in the course of an individual disease, limited historical data and newly emerging physical findings may make accurate diagnosis difficult • Following the patient’s clinical course or response to therapy may allow time for the disease to declare itself
Don’t be afraid to RE-THINK • If the clinical course or therapeutic response is not consistent with the original diagnosis, then that diagnosis must be questioned • For example, if the disease worsens unexpectedly or the patient’s symptoms persist despite adequate medical therapy, the physician must not persist in their presumption that the original diagnosis was correct • Western physicians will turn to the medical literature or their colleagues for another opinion
Student Intern Resident Staff • As they are just beginning their medical training, students have a less exhaustive understanding of disease presentation, and so cannot narrow their history and physical to only the most relevant topics • With time and experience the student becomes more adept at the process of obtaining a relevant, focused history, performing a directed physical examination, and the like
Student Intern Resident Staff • With time, students learn to incorporate a dynamic approach to the differential diagnosis • This allows them to reassess diagnostic possibilities throughout the entire process – not just after the basic information has been obtained
Dynamic Process • This intuitive style of thinking has been ingrained into the minds of Western physicians • The process begins at the onset of the patient’s presentation and then drives the entire patient encounter – directing further questioning, examination, and diagnostic testing • In cases where clinical course or response to therapy is inconsistent with the original diagnosis, return to the differential leads the physician in a new direction • In every sense of the word, differential diagnosis is a dynamic process.