Differential Diagnosis1

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Differential Diagnosis

The cornerstone of

Western medicine


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Initial thoughts. . .

Each question asked during the patientinterview reflects a sign, symptom, or risk

factor for a disease that we feel mayexplain the patients presentation.

Differential diagnosis directs our patientencounter from the very beginning.


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Patient encounter

Differential Diagnosis

History Physical

Diagnostic testing

Final diagnosis

Static Process


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PHYSICAL

DIFFERENTIAL

HISTORY

Dynamic Process


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Where do we begin?

Use available information

Age

Gender

Chief complaint

Vital Signs

Chart Review (as applicable)


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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


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Studying is important!

Understanding of epidemiologyAge, 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?


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Diagnosis may be made simply. . .


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Or not so simply. . .


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Formal Differential

Not needed: Classic presentation of common disease

Risk of acute mortality

Needed: Atypical disease presentation

Examination or testing does not confirm suspecteddiagnosis

Multiple signs and symptoms with no obviousconnection


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When you hear hoof beats. . .

think horses


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Occams Razor

A principle attributed to the 14th centurylogistician and Franciscan friar, William ofOckham

Pluralitas non est ponenda sine neccesitate

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

That is. . . Keep it SIMPLE!!


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Intuitive Postulates

Consider each sign or symptom individually

Generate a separate differential for each of thepatients 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.


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How to proceed. . .

Infection, neoplasm, meds/drugs, and exposureare the most likely categories

Neoplasm, trauma, meds/drugs can be ruled-outconvincingly by further history alone

Exposure may be difficultis the patient aware?

DIRECT questioningspecific possibilities


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Proceeding. . .

After ranking categoriesbegin to thinkabout specific diagnoses

In this caseinfection is most probable

List out specific infectious etiologies


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INFECTION

Infectious Mononucleosis (Epstein Barr - EBV)

Upper respiratory infection (rhinovirus,

paramyxovirus, etc.) Sinusitis

Measles

Varicella Pneumonia

Bronchitis


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Making the diagnosis

Using epidemiological data, history, andphysical we attempt to discover the

correct diagnosis

If our working diagnosis proves

inadequate, we return to the differentialand start anew


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Streamlined Process

Utilizing this more fluid thought process, as eachcategory is considered, specific diagnoses are

postulated simultaneously

As you develop the differential, more than onediagnosis may be plausible

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


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As illustrated here -

INFECTION

upper respiratory infection, sinusitis, EBV

EXPOSURE

insecticides, petroleum based chemicals or fumes

MEDICATION/DRUGS

inhalant abuse, medication overdose (aspirin)


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Epidemiology

The study of diseasein a specific population

Disease prevalence varies tremendously in different

patient populations

Students should become familiar with age, gender, andrace-related disease risk

In clinical study, understanding disease-specificepidemiology is equally important to knowledge ofdiagnosis and treatment


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Epidemiology is essential

Sinusitis remains the most probable diagnosis in lieu ofany further information

Young child who had not received standardimmunizations consider other infectious etiologies suchas varicella or measles, along with sinusitis

If this same young child had a history of exposure tosomeone with either of these illnesses, consideration ofthese diagnoses would be moved ahead of sinusitisaltogether


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Epidemiology is essential

Furthermore, the likelihood of pulmonary malignancy ina child would be infinitesimally small

16-year-old male who had recently spent numeroussleepless nights studying for final examinations, wewould strongly consider EBV infection

A 65 year old male with a life-long history ofconstruction work involving asbestos, then asbestosis orpulmonary malignancy might be considered beforesinusitis or EBV


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Developing a Thorough Differential

First review categories or areas of medicine

Once you had identified categories that areplausible, then proceed to specific diagnoseswithin those categories

This ensures that you consider ALL possibleareas of medicine and do not just focus on themost common


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VINDICATES

Vascular

Infectious, Inflammatory

Neoplastic

Drugs

Iatrogenic, Idiopathic/psychogenic

Congenital

Autoimmune (allergic)

Trauma

Endocrine (metabolic/nutrition), Exposure

Systems


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Rank-listing the differential

Ranking of differential makes the list ofdiagnoses more useful

Assuming that the diagnoses consideredadequatelyexplain the patients symptoms, thefinal order is based on two concepts

Most common/most likely diagnosis Diseases that are associated with high mortality or

morbidity


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But what do we do with the

zebras?


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Move uncommon disorders higher?

The diagnosis is plausible in our patient

Nearly impossible in our patient? Not necessary to consider itfrom the outsetregardless of lethality.

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

Diagnosis requires invasive study, specialized laboratory eval. orexpensive testing? It should remain toward the bottom of ourdifferential list

The diagnosis is associated with acute mortality

Diagnosis is associated with mortality only after a prolongedperiod of time? Consideration following further evaluation ofmore common disorders is advisable


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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 topof thedifferentialwith specific historical and physical datainfluencing 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 ofpossible etiologies


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Myocardial infarction?

Using the criteria outlined above, eliminating thepossibility of MI prior to final diagnosis is areasonable approach

The diagnosis is plausible, is associatedwithacute mortality, and can be ruled-out with aminimally invasive testElectrocardiogram

Enzymes (CKMB/Troponin) are rarely needed inthis scenario


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Teaching Points

If the patients presentation isconsistent with a rarediagnosis, then further evaluation by whatever meansnecessary is compulsory

The point is not to limit our evaluation in order to savemoney or timeinstead, diagnostic evaluation should bedriven by clinical indication

What is emphasized herein is that you must THINKthrough the process of deciding which diagnoses areconsidered first, and which can wait.


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The doctor as an artist

Each disease process does not present in exactly thesame way every time. Medicine is more than purescientific studyit is an art form

One cannot simply memorize key facts about a diagnosisand limit consideration of this disease to the fulfillmentof all necessary criteria alone

An astute physician recognizes the possibility of diseasepresenting atypically thereby not explaining every signor symptom


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Test of time. . .

Having made a final diagnosis, continued observation ofthe patient will allow us to determine if our suspicionwas correct

Students should recognize that uncovering the etiologyof disease may require time

Early on in the course of an individual disease, limitedhistorical data and newly emerging physical findings may

make accurate diagnosis difficult

Following the patients clinical course or response totherapy may allow time for the disease to declare itself


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Dont be afraid to RE-THINK

If the clinical course or therapeutic response is notconsistent with the original diagnosis, then thatdiagnosis must be questioned

For example, if the disease worsens unexpectedly or thepatients symptoms persist despite adequate medicaltherapy, the physician must not persist in theirpresumption that the original diagnosis was correct

Western physicians will turn to the medical literature ortheir colleagues for another opinion


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StudentInternResidentStaff

As they are just beginning their medical training,students have a less exhaustive understandingof disease presentation, and so cannot narrow

their history and physical to only the mostrelevant topics

With time and experience the student becomes

more adept at the process of obtaining arelevant, focused history, performing a directedphysical examination, and the like


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StudentInternResidentStaff

With time, students learn to incorporate adynamic approach to the differential

diagnosis

This allows them to reassess diagnosticpossibilities throughout the entire process

not just after the basic information hasbeen obtained


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Dynamic Process

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

The process begins at the onset of the patients presentation and

then drives the entire patient encounterdirecting furtherquestioning, examination, and diagnostic testing

In cases where clinical course or response to therapy is inconsistentwith the original diagnosis, return to the differential leads thephysician in a new direction

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


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DIAGNOSIS

DIFFERENTIAL H&P

TREATMENT

FOLLOW-UP

Dynamic Process

Documents

Differential Diagnosis1