Sim 1. Problem representation

Gathering information is the first step in diagnostic reasoning – an accurate history is the key to the correct diagnosis. A 1975 study queried doctors about their leading diagnosis after the history, after the exam and after labs. These were compared to the ultimate, correct diagnosis.  Eighty-two percent of the time, physicians arrived at the correct diagnosis after the history alone.  The exam led to the diagnosis 9% of the time, and labs and imaging to the other 9%.

This study was repeated in the 1990’s, when diagnostic tests were much more readily available,  with similar findings. In four out of five patients, expert clinicians arrived at the diagnosis after the history alone.   The physical exam and diagnostic testing are used for confirmation, but a detailed and accurate history is still the cornerstone of diagnostic reasoning.

The correct diagnosis is suggested by the history in four out of every five patients with a new concern.

The problem representation

As a patient tells their story, the most important pieces of data are synthesized into a problem representation in the clinician’s mind.  This problem representation activates illness scripts for ‘matching’ diseases that could be causing the patient’s symptoms.

Once a potential ‘match’ is identified, the physician checks it by gathering more information, comparing the patient’s symptoms and signs to what they know about that disease. Key information is added to the problem representation over the course of the H&P, with each iteration (ideally) bringing us closer to a correct diagnosis.

Your problem representations should be 1-2 sentences long and should include this diagnostically useful information.

• Patient demographics and predisposing conditions.
• Time course of illness.
• Clinical syndrome.

Demographics and predisposing conditions

The age of your patient is critically important in diagnostic reasoning – common causes of a given problem differ dramatically across the life span.

For some problems, sex is also important. Lower abdominal pain in a female patient could be caused by ovarian pathology or ectopic pregnancy on top of the appendicitis, diverticulitis and bladder infection that affect both females and males.

Predisposing conditions are medical problems or social conditions that are related to diagnoses that cause your patient’s concern. For example, high blood pressure is a predisposing condition for a patient presenting with chest pain since it’s a major risk factor for heart disease.  Recent incarceration is a predisposing condition for someone presenting with fever, as tuberculosis transmission is more common in that setting.  A history of recurrent UTIs is a predisposing condition for someone with lower abdominal pain – if it’s happened once it’s more likely to happen again.

You will become more confident in identifying predisposing conditions as you learn about different diseases in your Foundations blocks. For now, you can include major ongoing illnesses in your problem representation.

Timing of illness

Different diseases have different patterns of onset and progression, so a precise description of onset and time course can narrow your differential diagnosis. The onset of a patient’s symptoms can be described as hyperacute or sudden (minutes), acute (hours to days), subacute (days to weeks) or chronic.

The pattern of symptoms can also be diagnostically useful. It can be described as intermittent or constant; stable, progressive, or improving; relapsing or recurrent, waxing and waning.

Clinical syndrome

The word syndrome is derived from the Greek words meaning “running together.”  In medicine, it refers to a collection of symptoms & signs, often with a specific medical term, like “monoarticular arthritis.” You’ll learn about many syndromes over the course of Foundations.

For now, start with your patient’s chief concern and add any other symptoms that came on around the same time and seem important to you.

You should also add appropriate semantic qualifiers to describe the chief concern.  Semantic qualifiers are pairs of words that divide causes of a problem into different categories, each due to a different set of illnesses. By limiting the location, severity, and time course of a problem, they make the problem representation more precise, narrow the differential diagnosis, and reduce cognitive load.

Some semantic qualifiers are specific to a single chief concern.  For example, chest pain may be pleuritic (worse with a deep breath) or non-pleuritic. A cough may be productive or non-productive of sputum.  These two categories of each symptom have a very different differential diagnosis.

Semantic qualifiers that may used across many concerns include:

• Left or right
• Anterior or posterior
• Superficial or deep
• Proximal or distal
• Mild or severe
• Improving or worsening
• Sharp or dull
• Radiating or non-radiating
• Exertional or non-exertional

Placing the problem in context

Siting the current problem in the context of your patient’s overall health can also improve your differential.  Your patient’s problem list provides that big picture: Chronic illnesses, health behaviors and risks, acute problems that could recur, and social factors that impact health are all documented on the problem list, often in a specific area of the EHR

To prepare for the back pain simulation

Read Chapter 54, Low Back Pain from The Patient History: An Evidence Based Approach to Differential Diagnosis.  Pay careful attention to the diagnostic schema that is presented and to the semantic qualifiers that are important in characterizing back pain.  These will support your clinical reasoning as you assess your simulated patients!

Resources and references:

Problem representation overview. Journal of General Internal Medicine. Includes case examples that will make more sense after a few more blocks.