How can we understand disease? In search of “best evidence”. Triangles, Diseases, and Illness in the History of Medicine.

Is it real? In the busy family medicine clinic, I am talking to a middle aged woman with a new diagnosis of diabetes. Even though she is reasonable and intelligent, she doesn’t really buy into it. I’d rather not be on medication. I feel fine. She’s right, but I know what could happen to her if she’s untreated.

What is a disease? Who is a patient?

These are fundamental questions to medicine. Studying the history of medicine allows you a deeper understanding of diseases. This is important because it has implications on what we are actually doing as medical students / future health professionals.

Maybe surprisingly, we don’t ask the question “what is a disease” very often in the medical school curriculum. It’s obvious most of the time; a problem in anatomy or physiology is a disease. Tuberculosis, diabetes, and thyroid cancer are all obviously diseases.

The closest the pre-clerkship curriculum comes to asking “what is a disease” directly is through psychiatry course in pre-clerkship. According to the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders (the “DSM”), the definition of a disease depends on symptoms, but requires also a “functional deficit”. This means the symptoms must interfere with your life. According to this model, if a person had persistent low mood, changes in appetite, and visual hallucinations, (all symptoms of major depression), but was still able to function (ie. go to work or school), he would not have the mental disease we call depression.

Answering the question “what is a disease” is out of the scope of this blog post, and there is more nuance to the DSM in that functional deficit can include emotional distress, which I will also put aside. What about my patient who was unconcerned with her high blood sugar over the past year? If she is able to go to work, and is not bothered by it, does she avoid having the disease called diabetes? Before you say “no, obviously” In order to understand the diseases we treat today, it is helpful to know that disease is a changing entity.

The pyramid of evidence based medicine

At some point in every medical school, this triangle is studied.

The “triangle of evidence” describes modern biomedical science in a single figure.

The picture describes a hierarchy of scientific studies. There are many variations on it, but the essentials are as follows: individual patient experiences (case series), and expert opinions are nearest to the bottom, while randomized large sample trials are nearer to the top. Even higher are “reviews” which average out multiple RCTs. The point is to average out as many patients as possible to average out the noise and arrive to an answer.

Nearly every one of these graphs has an arrow pointing upwards, reminding us which way to move. Strictly, the higher we go on the chart the more strength there are for causal claims. Most graphs drop the nuance and just say “increasing strength” or “increasing quality”.

The triangle is powerful, and this process provides medicine with practical answers to questions about causality. It has been applied to every area of medicine.

I argue that, while a powerful approach, EBM has a great weakness.

III. Duffin’s Hippocratic Triangle

The triangle of evidence is so commonplace it’s difficult to imagine what medicine looks like without it.

There were many scientific advances which dramatically revolutionized medicine – around 1900 germ theory is developed and doctors began to think about pathology at the level of cells. New ways are developed to look into the body and these become .the gold standard.

Before all this, diseases were primarily defined by symptoms, and the model for disease was based upon a balance of four humors – theoretical fluids filled in the body. For example, jaundice was caused by an excess of yellow bile.

The core of medicine was not in cells, but instead the ability to care for patients (from Latin patientem meaning “one who suffers”).

Dr. Jacalyn Duffin, a hematologist and historian, develops a different triangle in order to teach what a disease is which is rooted in history. By Hippocratic teaching, a disease is made up on a combination of the observer (the physician), the patient, and the illness. Two patients, being different people, have different experiences even with the same illness being treated by the same doctor – this means they have different diseases! Crucially, the observer (doctor or medical student) also makes up a part of the disease.

This triangle also lacks a hierarchy. There is no clear way “up” – the doctor, the illness, and the patient are equally important in defining a disease. In contrast, the “case report”, is always on the bottom rung of the EBM.

How does this help?

It’s good to know that metformin works to reduce blood sugars in diabetes. Even though the evidence is backed by RCTs, some diabetic patients do not take their prescribed medications. The medical term for this behaviour is noncompliance or denial. Often medical trainees and doctors can find this frustrating.

Being aware of Duffin’s triangle (and the history of medicine) makes you understand that the patient’s experience with an illness will actually produce a different disease every time. The triangle also reminds us that the physician matters. Diabetes, then, is not simply just abnormal blood values. Validating the “noncompliant” patient’s experience changes the disease.

Further reading

  1. Duffin ‘s book Livers and Lovers uses explores changing disease concepts over time
  2. Podcast lecture on the history of the stethoscope. This is related to the transition in medicine,

About the Author: Ariel Gershon

Ariel Gershon (Meds 2019) completed a BSc at the University of Toronto in pathobiology before starting at Schulich. He was a president of Schulich’s Osler Society from 2016-2017, a group of medical students who meet to talk about the history of medicine over lunch. He‘s interested broadly in the medical sciences, medical humanities, and indoor gardening. Tweet at me @GershonMD2019


Photo Credits: Featured Image; Internet Archive Book, Creative Commons
Header Image; Ryan Adams, Creative Commons