What is a Disease, Really?
It's not as simple as you might think!
In a previous post, Practicing Medicine, I described the process by which doctors arrive at a diagnosis.
As I told it, the story involved three characters: the patient, the doctor, and the disease. Their interactions were archetypal. The patient was once healthy but is now unhealthy. They consult the doctor, who asks questions, does an exam, runs some tests, and then assigns a diagnostic label. Having identified the specific disease, the patient and doctor know what to expect and what to do.
But what is a disease?
In the context of the story, you might imagine the disease to be something that the patient has now but didn’t have before, like an unwanted houseguest.
This way of thinking originated in the 17th century and progressed rapidly throughout the 20th century. Like the species of animals or plants, diseases are imagined to be discrete entities which can be discovered, defined, characterized, and classified through a stepwise process:
Clinicians recognize a syndrome, a cluster of symptoms that seems to be shared by a group of patients.
The syndrome description is fleshed out through the inclusion of “typical” findings on physical examination (signs), and later by the results of blood tests, x-rays, biopsies, etc.
Once there seems to be some consistency, the specific combination of symptoms, signs and test results are translated into diagnostic “criteria”, facilitating both clinical care and research.
Through observation over time, we learn the “natural history” of the disease, including the time course, possible outcomes, complications, etc. Of note, some diseases are lifelong, so this step can take decades.
Research eventually reveals the root cause and mechanisms of the disease (the “pathophysiology”).
Knowing these, a remedy can be developed, ideally one which works specifically on the cause of the problem, altering the natural history for the better, with no side effects.
Disease entities thus defined can be grouped in various ways; acute or chronic, acquired or congenital, slow-growing or rapidly fatal, benign or malignant, infectious or metabolic, etc.
The full body of knowledge can be shared widely through teaching, textbooks, etc..
Thinking in this simplistic way, diseases are like weeds. Some are small, some large. Some come and go, while others take over, choking out everything else. Herbicides work sometimes, as long as they aren’t too toxic to yourself or your other plants.
Similarly, as your life progresses, you will likely “acquire” one or more of the thousands of available diseases. Some will be merely annoying, others more serious or even fatal. Some come and go, others stay. Some fixes work, others don’t.
Success!
Because it seems to work, this approach remains popular with doctors and patients alike.
Consider, for example, Type 1 Diabetes:
It was first recognized as a stereotypical cluster of symptoms involving increased thirst, increased urination, increased eating, blurred vision, and weight loss.
Further investigation revealed that many patients with these symptoms had alarmingly high blood sugar readings.
Untreated, the condition would progress quickly to ketoacidotic coma1 then death.
In time, it was found that the root cause of the problem was that the pancreas was no longer producing insulin, apparently because the immune system had destroyed the insulin-producing islet cells.2
The ideal remedy would involve resetting the immune system and then restoring a population of islet cells in the pancreas, so that they would once again produce insulin. However, that has proven to be difficult. The next best solution is to administer insulin, which quickly brings down the blood sugar and prevents immediate death. We have refined the types of insulin available and how insulin is administered.
Now that we’ve altered the natural history, the patients live longer, revealing numerous other complications that can take years to develop. Some of those complications are caused by the treatment (like low blood sugar, known as hypoglycemia), while others are due to the disease process (like damage to the small blood vessels in the eye, known as retinopathy). We’ve found ways to reduce or manage the complications, but it’s not perfect.
Whole books have been written about the care of diabetic patients.
Type 1 Diabetes is classified as a chronic, acquired, autoimmune disorder affecting the endocrine system.
On the whole, Type 1 Diabetes seems to be a pretty good example of how well the “disease entity” approach works.
When disease entities are carefully defined in this way, attaching diagnostic labels to patients does serve a purpose. Saying that a patient has Type 1 Diabetes is a quick way to communicate a lot of information about their disorder, the underlying causes, the problems they are likely to encounter along the way, and which treatments are likely to work. Knowing that someone has a specific disease often confers a different “status” in society, including myriad “benefits” such as sympathy, disability payments, reduced taxation, sick time, workplace accommodations, assistance with personal care, preferred parking, financial assistance for medical care, etc.
However…
There are some significant and surprisingly common problems with this approach:
Symptoms describe a patient experience. Patients don’t necessarily experience or describe the same symptom the same way. Symptoms alone don’t guarantee that a disease is present. The same cluster of symptoms can be caused by different diseases, and, conversely, one disease can present with different symptoms in different people.
Abnormal physical signs and tests are essential if we hope to define the disease and then learn about its causes and treatment, while separating the groups of patients with similar symptoms but different diseases. Some symptom clusters are proposed as diseases but no associated “objective” abnormalities are ever identified.3
It can be difficult or impossible to identify the root cause of a disease. In some disease syndromes, there may be more than one possible root cause, meaning that similar patients actually have different problems. Sometimes we postulate a cause with little or no proof.4
Even when we know the root cause(s), we may not be able to correct the problem(s).5
The treatments can create additional problems.6
The natural history of any given disease can be short or lifelong. Sometimes we don’t spend enough time learning the natural history. Some diseases resolve without outside intervention, creating the false impression that useless interventions work.7
Attaching disease labels to patients can be a waste of time (at best8) or dangerous (at worst9) when we don’t know the cause of their problem, when we don’t know the prognostic implications, and/or when there’s no effective treatment.
Etc.
In this and future posts, I’ll consider many of these challenges in greater detail. They each affect medical care at the individual doctor-patient level and they have implications for the healthcare system as a whole.
There’s a big, fundamental problem!
First, however, let’s consider the problem with the foundational idea that diseases are discrete entities.
Unlike those unwanted houseguests or the weeds in your garden, diseases don’t exist outside their human host. Without you, for example, that influenza virus is just an inanimate clump of protein and nucleic acid, doing nothing. Once inside you, however, it triggers a cascade of damaging events.
That being the case, diseases are simply the outward expression of abnormal or damaged structures or functions inside your body. Any clinical syndrome reflects the interplay between your bodily systems and whatever it is that causes your disease.
No two people are exactly the same, as I explained in my previous post, The Mystery of Modern Medicine. Any given disease affecting you will look somewhat like it does in other people with the same disease and yet it will also be unique to you. Imagine that you are the canvas, linen, board, or paper and the disease-causing agent is the pigment or paint. There are thousands of possible pictures, some similar but many quite different.
You, your spouse and your aging parents may all be exposed to the same strain of “the flu” at roughly the same time, but the ensuing illness will not be identical for all of you. You have immunity and don’t get sick. Your spouse has partial immunity and gets mildly ill, while your parents end up flat on their back in bed, in hospital or even dead. This gets even more complicated when you consider the various strains of influenza virus, each with their own properties.
Going one step further, when you get sick some of your symptoms reflect the disease itself, some reflect the bodily disruptions caused by the disease, and some reflect your other body systems attempting to compensate. For example, in Type 1 Diabetes the frequent urination reflects your kidney’s attempt to pee out the excess sugar, while ketoacidosis and weight loss result from your liver breaking down body fat as an alternate source of fuel for your cells. In pneumonia, as another example, those cloudy patches seen on the chest x-rays include the white blood cells that your immune system sent there to fight the infection.
So, in practical terms, it’s not enough to look at your Type 1 Diabetes or any other disease as simply an unwanted houseguest to be evicted, because the behaviour of your “guest” before, during and after treatment reflects, at least in part, your body’s response to the unwelcome visit.10
For that reason, the “nuclear option” (blowing up the disease) is rarely an option, because to kill your disease would be to kill you. We could clean up those pneumonia patches on your chest x-ray by suppressing your immune system, but that would allow the infection to run rampant. Instead, we use antibiotics to weaken the bacteria that cause the pneumonia, and we rely on your immune system to mop up the infection. However, that approach may fail if your immune system isn’t functioning well, or if your lungs weren’t normal in the first place, maybe because you’ve been smoking for decades.
As another example, while your surgeon can excise your diseased appendix, your body still has work to do after the fact, cleaning up any residual infection and healing up that surgical incision.
All of which is to emphasize that you and your disease are inextricably linked. It’s not like you went to the store, took a disease off the shelf, and later decided that you wanted to return it for a full refund. It was never there on the shelf in the first place! It was part of you from the get go. By the time you’ve decided that you don’t like it, it’s too late! If you’re lucky, your disease might be like a bad haircut that will grow out, or, like the paint colour that you hate the moment it dries on the wall, it will be something unfortunate that can be painted over.
Unfortunately, however, a lot of diseases are more permanent. Once you have Type 1 Diabetes, it’s yours to live with until you die. Its behaviour will always reflect the things your body systems do to compensate for the lack of insulin, as well as the work you do regarding diet, lifestyle, blood glucose monitoring, insulin adjustments, regular follow-up, tests, etc. Your medical team are there to help, but they’ll never chase the beast out of your body. You can “battle” diabetes if you like, but you’ll never declare victory. You go from being a “person” to being a “diabetic”, but that doesn’t mean that you are defined by your disease. It means that you are now “a person living with diabetes”, while the other facets of your personhood go on. You may never come to see your diabetes as a friend, but you will need to accept that it’s your permanent companion.
So what?
I’ve belabored the relationship between the human body and its diseases for a reason.
When a disease is seen as a discrete entity, hiding within the body, there’s a tendency to focus more on the disease and less on the person.
For the doctor, once they’ve determined the underlying explanation for your symptoms, it becomes far too easy to look past you and your experience of the disease and its treatment (the “subjective” story). Instead, they start to focus on the abnormal anatomy and physiology lurking within you (the “objective” target). This hyper-focus on the disease sometimes means, for example, that your cancer doctor sees themselves as personally doing battle with the cancer in your lung, even as they neglect to consider the quality of your life as a person living with cancer, the role that you play in the treatment plan, and how your values and beliefs might affect the therapeutic choices. They might forget to ask “how are you doing?” and “what do you want to accomplish?”, while they are pleased that the x-ray looks no worse. Carried to an extreme, this plays out as the scenario in which “the operation was a success but the patient died”.11
For some patients, receiving a diagnosis provides a sense of relief, validation, legitimization, and empowerment, allowing them to see their disease in a more detached way. Carried to an extreme, however, this detachment sometimes leads to the notion that the individual must “battle” their disease, as if it were an invading army. The battle metaphor is generally thought to be unhelpful, particularly with cancer. It unrealistically implies that a patient who fights hard enough and/or long enough will win, while those who do die of their cancer are portrayed as losers. In fact, the outcome reflects the interplay between the disease and the bodily systems, while individual effort has little to do with cancer survivorship. Some suggest that living with cancer might be better conceived of as a journey, the cancer being a fellow traveler.12
For other patients, their disease becomes their identity, or a large part of it. Some patients describe themselves in terms of their current or previous symptoms or diseases, saying things like “I have severe anxiety” or “I’m a cancer survivor”. In doing so, they use the label to encapsulate and even oversimplify their experience of the illness, while failing to acknowledge that each patient’s experience will be unique. How far do we go to avoid adding further stress to the already anxious person? How does one respond to the patient who publicly describes themselves as a “cancer survivor” when their cancer was of a type that was unlikely to be fatal, requiring minimal treatment?13
And what about patients who have received a diagnosis without pursuing any treatment, as, for example, many of those with addictions and/or mental health issues living on the street? Are they to be excused from their societal obligations and forgiven for their illegal behaviours? To what extent can they blame the “disease within” for their troubles without considering their role as the “person living with the disease”?14
Going one step further, what of the patient who describes themselves in terms of their self-diagnosed malady, never having seen a doctor or having had any objective confirmation of their diagnosis. Do we accept that the prognostic and therapeutic implications of the diagnosis apply in their case and grant them the medical and societal treatment that goes with their disease? What if their self-diagnosis is wrong?15
In Conclusion…
Diseases are often thought of as real entities, with a life of their own.
While this approach has shown some success, there are significant problems, including how people with diseases see themselves, how they interact with their doctors, and how they are treated by society as a whole.
Rather than thinking of diseases as bodily invaders, I’m suggesting that they be seen as traveling companions. Dealing with illness then becomes less of a battle and more of a journey.
What’s Next?
In a future post, I’ll look at symptom clusters.
For any number of reasons, it’s become “fashionable” to suggest that various symptoms, alone or in groupings, represent “new” diseases for which causes are postulated and treatments proposed.
This creates problems, as you will see.
A type of coma defined by the build-up of chemicals called ketones, which cause the blood to become too acidic.
Nobody knows exactly why this happens. It’s believed to be a combination of environmental and genetic factors, which is what we say in medicine when we honestly have no clue!
Chronic Fatigue Syndrome is one such example. It’s also known as Myalgic Encephalopathy, which sort of implies that it’s a brain disorder, but nobody has yet proven that there are any abnormalities in the brain.
One example being the notion that low levels of serotonin in the brain cause depression, leading to the widespread use of Selective Serotonin Reuptake Inhibitors (SSRI’s). It turns out there’s not much evidence to support those low serotonin levels!
Huntington’s Disease being but one example among thousands.
Consider the toxicities of chemotherapy and radiotherapy in cancer treatment, or the fact that antirejection drugs make transplant patients more susceptible to infections.
This explains all sorts of treatments over the years that were once popular but later discredited, anything from bleeding and purging centuries ago through to antibiotics for ear infections in more recent times.
Covid is an example where attaching the disease label has become a waste of time. For the majority of patients, Covid looks like any other viral upper respiratory infection, for which the best approach is simply to avoid spreading the infection while resting and waiting for the symptoms to settle, as they are likely to do within days. Sicker patients should seek medical care, regardless of whether they have Covid, influenza, or some other virus. Covid rapid tests offer no useful information in terms of treatment, prognosis, or the need to isolate.
Many argue that a number of the mental health disorders defined in the Diagnostic and Statistical Manual are actually harmful when used to label patients. They argue that the criteria are inconsistent and subjective, with significant overlap between diagnoses. Incorrect labelling can lead to medicalization of normal emotional responses, while leading to stigma and prejudice.
It’s an example of “We have met the enemy, and he is us”, or, more accurately, “…he is partly us”!
You also see this in hospital care. Some elderly patients are parked in bed and loaded up with medications to fix their disease, only to find, a week later, that they’ve become so weak from inactivity that they can’t get out of bed!
See, for example, Losing “Losing the Battle With Cancer”
On this note, I’ve sometimes been known to refer to myself as a “motor vehicle accident survivor”, having been involved in half a dozen minor collisions over the years.
In a future post I’ll compare and contrast the approaches to Alcohol Use Disorder (AUD) and Opioid Use Disorder (OUD). The treatment of AUD generally emphasizes the responsibilities of the person living with the disease, and the most effective approach involves accepting that there’s a problem while avoiding alcohol and the triggers for drinking. OUD on the other hand is characterized as a medical disorder of the brain, where only drugs can fix the problem. Nobody would ever suggest using alcohol to treat alcoholism, whereas it’s standard practice to use opioids to treat OUD.
This is already happening in children with gender dysphoria, where the immediate response is to validate their self-diagnosis, for fear of causing harm by questioning it.
Excellent post. It actually reminded me of the age-old debate between Louis Pasteur and Antoinne Beauchamp regarding germs or terrain as the cause of disease. The reality is that both are important. Unfortunately, most people view medicine as only a scientific process devoid of art, whereas the truth is closer to being an art with scientific aspects. Sadly, the 5-10 minute history taking in clinical practice is a product of financial interests rather than medical best practice which could be called an art and diseases are viewed in a reductionist way rather than as variable processes to satisfy those financial interests. I particularly like your example of the treatment of AUD and OUD. Be Well