Differential DiagnosisDifferential Diagnosis

The cornerstone ofThe cornerstone of

Western medicineWestern medicine

Initial thoughts. . .Initial thoughts. . .

Each question asked during the patient Each question asked during the patient interview reflects a sign, symptom, or interview reflects a sign, symptom, or risk factor for a disease that we feel risk factor for a disease that we feel may explain the patient’s presentation. may explain the patient’s presentation.

Differential diagnosis directs our patient Differential diagnosis directs our patient encounter from the very beginning. encounter from the very beginning.

Patient encounterPatient encounter

Differential Diagnosis

History Physical

Diagnostic testing

Final diagnosis

Static ProcessStatic Process

PHYSICAL

DIFFERENTIAL

HISTORY

Dynamic Dynamic ProcessProcess

Where do we begin?Where do we begin?

Use available information Use available information AgeAge GenderGender Chief complaintChief complaint Vital SignsVital Signs Chart Review (as applicable)Chart Review (as applicable)

Thought process. . .Thought process. . .Epidemiology, Chief complaint, Vital signs

Differential diagnosis

Focused history and physical

Refine differential diagnosis

Final diagnosis

Further history or physical

Diagnostic testing

Problem List

Studying Studying isis important! important!

Understanding of epidemiologyUnderstanding of epidemiology Age, gender, raceAge, gender, race

Knowledge of disease presentationKnowledge of disease presentation Which diseases present with cough, which with Which diseases present with cough, which with

fever, acute versus chronic symptoms, etc.fever, acute versus chronic symptoms, etc.

Ability to recognize abnormal vital signsAbility to recognize abnormal vital signs Is the patient hypertensive? Tachycardic? Is the patient hypertensive? Tachycardic?

Febrile? Febrile?

Diagnosis may be made Diagnosis may be made simply. . .simply. . .

Physical

Vital Signs History

Chief complaint

Epidemiology

Final diagnosis

Or not so simply. . .Or not so simply. . .

Follow-up

MedicationTrial

Diagnostictesting

Formal differential Review

of systems

Physical

History

Vital Signs

Chief complaint

Epidemiology

Final Final diagnosisdiagnosis

Formal DifferentialFormal Differential

Not needed:Not needed: Classic presentation of common diseaseClassic presentation of common disease Risk of acute mortalityRisk of acute mortality

Needed:Needed: Atypical disease presentationAtypical disease presentation Examination or testing does not confirm Examination or testing does not confirm

suspected diagnosissuspected diagnosis Multiple signs and symptoms with no obvious Multiple signs and symptoms with no obvious

connectionconnection

When you hear hoof beats. . When you hear hoof beats. . . .

t think hink horseshorses

Occam’s RazorOccam’s Razor

A principle attributed to the 14th century A principle attributed to the 14th century logistician and Franciscan friar, William of logistician and Franciscan friar, William of OckhamOckham

““Pluralitas non est ponenda sine Pluralitas non est ponenda sine

neccesitate”neccesitate”

Plurality (numerous ideas) should not be Plurality (numerous ideas) should not be posited (considered) without necessityposited (considered) without necessity

That is. . . Keep it SIMPLE!!That is. . . Keep it SIMPLE!!

Intuitive PostulatesIntuitive Postulates Consider each sign or symptom individuallyConsider each sign or symptom individually

Generate a separate differential for each of the Generate a separate differential for each of the patient’s issuespatient’s issues

Compare the problem-specific differentialsCompare the problem-specific differentials

Include diagnoses that appear frequentlyInclude diagnoses that appear frequently Those which explain all pertinent positive findings.Those which explain all pertinent positive findings.

Exclude diagnoses that appear infrequentlyExclude diagnoses that appear infrequently Diagnoses that do not explain a majority of findings Diagnoses that do not explain a majority of findings

are unlikely candidates. are unlikely candidates.

O/W healthy patient with. . .O/W healthy patient with. . .“cough, fever, headache, tired”“cough, fever, headache, tired”

CoughCough FeverFever HeadachHeadachee

FatigueFatigue

infectioninfection autoimmunautoimmunee

vascularvascular nutritionnutrition

traumatrauma infectioninfection exposureexposure metabolicmetabolic

congenitalcongenital inflammatioinflammationn

neoplasmneoplasm infectioninfection

exposureexposure endocrineendocrine neurologicneurologic endocrineendocrine

meds/drugsmeds/drugs neoplasmneoplasm psychogenipsychogenicc

meds/drugsmeds/drugs

neoplasmneoplasm meds/drugsmeds/drugs infectioninfection exposureexposure

neurologicneurologic metabolicmetabolic meds/drugsmeds/drugs neoplasmneoplasm

psychogenipsychogenicc

exposureexposure traumatrauma autoimmunautoimmunee

How to proceed. . .How to proceed. . .

Infection, neoplasm, meds/drugs, and Infection, neoplasm, meds/drugs, and exposure are the most likely categoriesexposure are the most likely categories

Neoplasm, trauma, meds/drugs can be ruled-Neoplasm, trauma, meds/drugs can be ruled-out convincingly by further history aloneout convincingly by further history alone

Exposure may be difficult – is the patient Exposure may be difficult – is the patient aware?aware?

DIRECT questioning – specific possibilitiesDIRECT questioning – specific possibilities

Proceeding. . .Proceeding. . .

After ranking categories – begin to After ranking categories – begin to think about specific diagnosesthink about specific diagnoses

In this case – infection is most In this case – infection is most probableprobable

List out specific infectious etiologiesList out specific infectious etiologies

INFECTIONINFECTION

Infectious Mononucleosis (Epstein Barr - Infectious Mononucleosis (Epstein Barr - EBV)EBV)

Upper respiratory infection (rhinovirus, Upper respiratory infection (rhinovirus, paramyxovirus, etc.)paramyxovirus, etc.)

SinusitisSinusitis MeaslesMeasles VaricellaVaricella PneumoniaPneumonia BronchitisBronchitis

Making the diagnosisMaking the diagnosis

Using epidemiological data, history, Using epidemiological data, history, and physical we attempt to discover and physical we attempt to discover the correct diagnosisthe correct diagnosis

If our working diagnosis proves If our working diagnosis proves inadequate, we return to the inadequate, we return to the differential and start anewdifferential and start anew

Streamlined ProcessStreamlined Process

Utilizing this more fluid thought process, as Utilizing this more fluid thought process, as each category is considered, specific each category is considered, specific diagnoses are postulated simultaneously diagnoses are postulated simultaneously

As you develop the differential, more than As you develop the differential, more than one diagnosis may be plausibleone diagnosis may be plausible

In this case the final differential is In this case the final differential is comprised of the top possibilities in each of comprised of the top possibilities in each of medical categorymedical category

As illustrated here -As illustrated here -

INFECTIONINFECTION upper respiratory infection, sinusitis, EBVupper respiratory infection, sinusitis, EBV

EXPOSUREEXPOSURE insecticides, petroleum based chemicals or insecticides, petroleum based chemicals or

fumesfumes

MEDICATION/DRUGSMEDICATION/DRUGS inhalant abuse, medication overdose (aspirin)inhalant abuse, medication overdose (aspirin)

EpidemiologyEpidemiology

The study of The study of diseasedisease in a specific population in a specific population

Disease prevalence varies tremendously in Disease prevalence varies tremendously in different patient populationsdifferent patient populations

Students should become familiar with age, Students should become familiar with age, gender, and race-related disease riskgender, and race-related disease risk

In clinical study, understanding disease-specific In clinical study, understanding disease-specific epidemiology is equally important to knowledge epidemiology is equally important to knowledge of diagnosis and treatmentof diagnosis and treatment

Epidemiology is essentialEpidemiology is essential

Sinusitis remains the most probable diagnosis in Sinusitis remains the most probable diagnosis in lieu of any further informationlieu of any further information

Young child who had not received standard Young child who had not received standard immunizations immunizations consider other infectious consider other infectious etiologies such as varicella or measles, along with etiologies such as varicella or measles, along with sinusitissinusitis

If this same young child had a history of exposure If this same young child had a history of exposure to someone with either of these illnesses, to someone with either of these illnesses, consideration of these diagnoses would be moved consideration of these diagnoses would be moved ahead of sinusitis altogether ahead of sinusitis altogether

Epidemiology is essentialEpidemiology is essential

Furthermore, the likelihood of pulmonary Furthermore, the likelihood of pulmonary malignancy in a child would be infinitesimally smallmalignancy in a child would be infinitesimally small

16-year-old male who had recently spent 16-year-old male who had recently spent numerous sleepless nights studying for final numerous sleepless nights studying for final examinations, we would strongly consider EBV examinations, we would strongly consider EBV infectioninfection

A 65 year old male with a life-long history of A 65 year old male with a life-long history of construction work involving asbestos, then construction work involving asbestos, then asbestosis or pulmonary malignancy might be asbestosis or pulmonary malignancy might be considered before sinusitis or EBV considered before sinusitis or EBV

Developing a Thorough Developing a Thorough DifferentialDifferential

First review categories or areas of First review categories or areas of medicinemedicine

Once you had identified categories that Once you had identified categories that are plausible, then proceed to specific are plausible, then proceed to specific diagnoses within those categoriesdiagnoses within those categories

This ensures that you consider ALL This ensures that you consider ALL possible areas of medicine and do not just possible areas of medicine and do not just focus on the most commonfocus on the most common

VINDICATESVINDICATES

VVascularascular IInfectious, Inflammatorynfectious, Inflammatory NNeoplasticeoplastic DDrugsrugs IIatrogenic, Idiopathic/psychogenicatrogenic, Idiopathic/psychogenic CCongenitalongenital AAutoimmune (allergic) utoimmune (allergic) TTraumarauma EEndocrine (metabolic/nutrition), Exposurendocrine (metabolic/nutrition), Exposure SSystemsystems

Rank-listing the differentialRank-listing the differential

Ranking of differential makes the list of Ranking of differential makes the list of diagnoses more usefuldiagnoses more useful

Assuming that the diagnoses considered Assuming that the diagnoses considered adequatelyadequately explain the patient’s symptoms, explain the patient’s symptoms, the final order is based on two concepts – the final order is based on two concepts – Most common/most likely diagnosisMost common/most likely diagnosis Diseases that are associated with high mortality Diseases that are associated with high mortality

or morbidityor morbidity

But what do we do with the But what do we do with the zebras?zebras?

Move uncommon disorders Move uncommon disorders higher?higher?

The diagnosis is plausible in our patientThe diagnosis is plausible in our patient Nearly impossible in our patient? Not necessary to consider Nearly impossible in our patient? Not necessary to consider

it from the outset – regardless of lethality.it from the outset – regardless of lethality.

The diagnosis can be eliminated by additional The diagnosis can be eliminated by additional history, physical examination, or non-invasive history, physical examination, or non-invasive testingtesting

Diagnosis requires invasive study, specialized laboratory Diagnosis requires invasive study, specialized laboratory eval. or expensive testing? It should remain toward the eval. or expensive testing? It should remain toward the bottom of our differential listbottom of our differential list

The diagnosis is associated with acute mortalityThe diagnosis is associated with acute mortality Diagnosis is associated with mortality only after a Diagnosis is associated with mortality only after a prolonged prolonged

period of time? Consideration following further evaluation period of time? Consideration following further evaluation of more common disorders is advisableof more common disorders is advisable

Sample case: Sample case: Adolescent patient with chest Adolescent patient with chest

painpain Common causes include pleurisy, costochondritis, Common causes include pleurisy, costochondritis,

benign overuse myalgia, or anxiety/stressbenign overuse myalgia, or anxiety/stress

As such, these diagnoses should appear at the As such, these diagnoses should appear at the toptop of the differential – with specific historical and of the differential – with specific historical and physical data influencing the final order physical data influencing the final order

Myocardial infarction (MI), while plausible, would Myocardial infarction (MI), while plausible, would be highly unlikely in an otherwise healthy childbe highly unlikely in an otherwise healthy child

Therefore, MI would be placed lower on the list of Therefore, MI would be placed lower on the list of possible etiologiespossible etiologies

Myocardial infarction?Myocardial infarction?

Using the criteria outlined above, Using the criteria outlined above, eliminating the possibility of MI prior to eliminating the possibility of MI prior to final diagnosis is a reasonable approachfinal diagnosis is a reasonable approach

The diagnosis is The diagnosis is plausibleplausible, is , is associatedassociated with acute mortalitywith acute mortality, and can be , and can be ruled-out ruled-out with a minimally invasive testwith a minimally invasive test ElectrocardiogramElectrocardiogram

Enzymes (CKMB/Troponin) are rarely Enzymes (CKMB/Troponin) are rarely needed in this scenarioneeded in this scenario

Teaching PointsTeaching Points

If the patient’s presentation If the patient’s presentation isis consistent with a consistent with a rare diagnosis, then further evaluation by whatever rare diagnosis, then further evaluation by whatever means necessary is compulsorymeans necessary is compulsory

The point is not to limit our evaluation in order to The point is not to limit our evaluation in order to save money or time – instead, diagnostic save money or time – instead, diagnostic evaluation should be driven by clinical indicationevaluation should be driven by clinical indication

What is emphasized herein is that you must What is emphasized herein is that you must THINKTHINK through the process of deciding which diagnoses through the process of deciding which diagnoses are considered first, and which can wait.are considered first, and which can wait.

The doctor as an artistThe doctor as an artist

Each disease process does not present in exactly Each disease process does not present in exactly the same way every time. Medicine is more than the same way every time. Medicine is more than pure scientific study – it is an art formpure scientific study – it is an art form

One cannot simply memorize key facts about a One cannot simply memorize key facts about a diagnosis and limit consideration of this disease diagnosis and limit consideration of this disease to the fulfillment of to the fulfillment of all all necessary criteria alonenecessary criteria alone

An astute physician recognizes the possibility of An astute physician recognizes the possibility of disease presenting atypically – thereby not disease presenting atypically – thereby not explaining every sign or symptom explaining every sign or symptom

Test of time. . .Test of time. . . Having made a final diagnosis, continued Having made a final diagnosis, continued

observation of the patient will allow us to determine observation of the patient will allow us to determine if our suspicion was correctif our suspicion was correct

Students should recognize that uncovering the Students should recognize that uncovering the etiology of disease may require timeetiology of disease may require time

Early on in the course of an individual disease, Early on in the course of an individual disease, limited historical data and newly emerging physical limited historical data and newly emerging physical findings may make accurate diagnosis difficultfindings may make accurate diagnosis difficult

Following the patient’s clinical course or response Following the patient’s clinical course or response to therapy may allow time for the disease to to therapy may allow time for the disease to declare itselfdeclare itself

Don’t be afraid to RE-THINKDon’t be afraid to RE-THINK

If the clinical course or therapeutic response is If the clinical course or therapeutic response is notnot consistent with the original diagnosis, then that consistent with the original diagnosis, then that diagnosis must be questioneddiagnosis must be questioned

For example, if the disease worsens unexpectedly For example, if the disease worsens unexpectedly or the patient’s symptoms persist despite or the patient’s symptoms persist despite adequate medical therapy, the physician must not adequate medical therapy, the physician must not persist in their presumption that the original persist in their presumption that the original diagnosis was correctdiagnosis was correct

Western physicians will turn to the medical Western physicians will turn to the medical literature or their colleagues for another opinionliterature or their colleagues for another opinion

StudentStudent Intern Intern Resident Resident StaffStaff

As they are just beginning their medical As they are just beginning their medical training, students have a less exhaustive training, students have a less exhaustive understanding of disease presentation, and understanding of disease presentation, and so cannot narrow their history and physical so cannot narrow their history and physical to only the most relevant topicsto only the most relevant topics

With time and experience the student With time and experience the student becomes more adept at the process of becomes more adept at the process of obtaining a relevant, focused history, obtaining a relevant, focused history, performing a directed physical examination, performing a directed physical examination, and the like and the like

StudentStudent Intern Intern Resident Resident StaffStaff

With time, students learn to With time, students learn to incorporate a dynamic approach to incorporate a dynamic approach to the differential diagnosisthe differential diagnosis

This allows them to reassess This allows them to reassess diagnostic possibilities throughout diagnostic possibilities throughout the entire process – not just after the the entire process – not just after the basic information has been obtainedbasic information has been obtained

Dynamic ProcessDynamic Process

This intuitive style of thinking has been ingrained into the This intuitive style of thinking has been ingrained into the minds of Western physiciansminds of Western physicians

The process begins at the onset of the patient’s The process begins at the onset of the patient’s presentation and then drives the entire patient encounter – presentation and then drives the entire patient encounter – directing further questioning, examination, and diagnostic directing further questioning, examination, and diagnostic testingtesting

In cases where clinical course or response to therapy is In cases where clinical course or response to therapy is inconsistent with the original diagnosis, return to the inconsistent with the original diagnosis, return to the differential leads the physician in a new directiondifferential leads the physician in a new direction

In every sense of the word, differential diagnosis is a In every sense of the word, differential diagnosis is a dynamicdynamic process. process.

DIAGNOSIS

DIFFERENTIAL H&P

TREATMENT

FOLLOW-UP

Dynamic Dynamic ProcessProcess