Differential Diagnosis

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Differential Diagnosis

• The cornerstone of
• Western medicine

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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 patients
  presentation.
• Differential diagnosis directs our patient
  encounter from the very beginning.

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Static Process
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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. . .
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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?

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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 suspected
  diagnosis
• Multiple signs and symptoms with no obvious
  connection

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When you hear hoof beats. . . think horses
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Occams 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!!

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Intuitive Postulates

• Consider each sign or symptom individually
• Generate a separate differential for each of the
  patients 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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O/W healthy patient with. . .cough, fever,
headache, tired
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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

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Proceeding. . .

• After ranking categories begin to think about
  specific diagnoses
• In this case infection 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, and physical
  we attempt to discover the correct diagnosis
• If our working diagnosis proves inadequate, we
  return to the differential and start anew

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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

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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 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

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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

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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

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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

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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 of
  diagnoses more useful
• Assuming that the diagnoses considered adequately
  explain the patients symptoms, the final 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 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

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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 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

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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 associated with
  acute mortality, and can be ruled-out with a
  minimally invasive test ? Electrocardiogram
• Enzymes (CKMB/Troponin) are rarely needed in this
  scenario

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Teaching Points

• If the patients 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 THINK
  through the process of deciding which diagnoses
  are considered first, and which can wait.

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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

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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 patients clinical course or
  response to therapy 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
  not consistent with the original diagnosis, then
  that diagnosis must be questioned
• For example, if the disease worsens unexpectedly
  or the patients 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

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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

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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

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Dynamic Process

• This intuitive style of thinking has been
  ingrained into the minds of Western physicians
• The process begins at the onset of the patients
  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.

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Dynamic Process