Differential Diagnosis

Or “How I learned to stop worrying and love the BALM”

Clinton Pong

Objectives

• Define “differential diagnosis”• Errors– aka how do you get the “right ddx”

• Develop a systematic, routine method for differential diagnosis generation– The BALM

The Challenge: What is a Ddx?

• Recognize a collection of signs and symptoms• Recall basic pathophysiology• Restate in terms of disease• Reconnect with the initial complaint

• Framing: pre-/post-test probability– Reframing: Reconsidering ddx when there is a

progression of unusual natural history

How many times have you done this?

• Premature closure of diagnosis– “Hm, this is the cardio unit and they have chest pain.

Duh. It’s a heart attack.”• The crazy “House” diagnosis– “Chest pain and shortness of breath?!? They could

have a worm like Strongyloides stercoralis that went up their gut into their lungs and then to their bloodstream!”

• The LI of the MINDNUMBING table of differentials A-Z + 1,2,3,4,5,6,7,8,9,10…

Cognitive Diagnostic Errors

Examples:• “Umm… trauma or cancer?”• “80 years old? I thought you

said 18 years old.”• “Psh. It’s just a little ____.”• “The ___ is (+) so it is ____.”• “The __ is (-) so it is not __.”• “It’s gotta be a ____.”

Errors• Faulty hypothesis generation• Faulty context formulation• Faulty information

gathering/processing– Inaccurate assessment of

prevalence or severity– Wrong interpretation of test– Overrreliance on clinical axiom

• Faulty verification– Premature closure of diagnosis

• “No-fault” errors

Many diagnostic errors occur because we try to fit the data to our hypothesis rather than

fitting the hypothesis to our data.

http://www.flickr.com/photos/epublicist/

http://www.medrants.com/?p=3629http://hlwiki.slais.ubc.ca/index.php?title=Long_tail#Impact_in_medicine

House, MD. White board

http://differentialdiagnosi.proboards.com/index.cgi?

Occam’s Razor:Quest for the Holy Parsimony

• “Plurality should not be posited without necessity.”

http://en.wikipedia.org/wiki/William_of_Ockham

Pluralitas non est ponenda sine necessitate

Sherlock Holmes

• "When you have eliminated the impossible, whatever remains, however improbable, must be the truth."

DeGowin’s Quotable:

• Disease is a four-dimensional story, which follows the biologic imperatives of its particular pathophysiology in specific anatomic sites as influenced by the unique characteristics of this patient.

• Your task is not verbal, but cinematic; construct a pathophysiologic and anatomic movie of the onset and progression of the illness: the words are generated from the images, not the images from the words.

Nobody ever needs to know that the instant you see lawyer [on the USMLE] you immediately think:

“Scumbag who sleeps with prostitutes and therefore has gonorrhea, syphilis, chlamydia, and herpes.”

It’ll stay our dirty little secret.

http://www.agraphia.net/zac-fact-10-bigot-your-way-to-success/

http://www.agraphia.net/zac-fact-10-bigot-your-way-to-success/

Race/EthnicityAfrican Americans have sarcoid and sickle cell.White kids have cystic fibrosis and can’t dance.Japanese people have stomach cancer and ninja skills.

LifestylesWomen are always pregnant. No matter how careful they were.Coke Addicts had an MI (don’t smoke crack, kids!)Patients with a swollen knee are female, young, hot, and caught gonorrhea from their last boyfriend.

Etc…

The BALM

• By systems• Acute vs Chronic• Local vs Systemic• MEDICINE DOC

• Great tier system for starting off your ddx

• Where is it?• Will it kill the patient?• What else can it do?• If all else fails, go to the

laundry list.

Framework• Acute vs Chronic

• Local vs Systemic

• High Probability – Incidence– (the most difficult part of the frame as a medical student)

– What is most likely? Rare Common• High Utility – Morbidity/Mortality– What do you want to

make sure you never miss? Benign Serious

The Systems ApproachMEDICINE• Metabolic/Medications• Endocrine• Degenerative• Infection/Ischemia/Infarction• Congenital• Iatrogenic/Idiopathic• Neoplastic• Electrical (Neuro/Psych)

Alternatively,• I VINDICATE AID• DIRECTION• VITAMIN C,D

PE organ systems list• Neuro• Lung• CV• GI• Renal/GU/GYN• Heme/ID• Endo

The Systems ApproachVITAMIN C, D & E• Vascular• Infection/Ischemia/Infarction• Trauma/Toxin• Autoimmune• Metabolic/Medications• Iatrogenic/Idiopathic• Neoplastic• Congenital• Degenerative• Electrical (Neuro/Psych)

Alternatively,• I VINDICATE AID• DIRECTION• MEDICINE

PE organ systems list• Neuro• Lung• CV• GI• Renal/GU/GYN• Heme/ID• Endo

By disciplineOB/GYN Peds IM/FM Surg Geri Psych

ABD painAbnormal mensesDysuria

FeverJaundiceGrowth problemsWheezeURI complaintsRash

CoughHeadacheChest PainSOBBack painKnee painLeg swelling

ABD painGI bleedingBowel obstructionTrauma

Altered mental statusFallsFractures

SadnessAnxietyAgitationDrug abuse/ Dependence

Hint hint…

Resources• Groopman, Jerome. How Doctors Think. Mariner Books © 2008.• Kassirer, Jerome. Learning Clinical Reasoning. Williams and

Wilkins. © 1991.• DeGowin's

Diagnostic Examination, Ninth Edition (Paperback) by Richard LeBlond (Author), Donald Brown (Author), Richard DeGowin (Author)

• http://en.wikipedia.org/wiki/William_of_Ockham• (Heuristics) Bigot your way to Success on the USMLE

– http://www.agraphia.net/zac-fact-10-bigot-your-way-to-success/• “Separating clinicians from automatons: the long tail”

– http://doctorrw.blogspot.com/2008/08/separating-clinicians-from-automatons.html