Sim 2. Developing Diagnostic Hypotheses

An illness scripts is an organized mental summary of information about a disease. Illness scripts are based on both medical knowledge and experience with patients, and they are unique to an individual clinicians. The cognitive psychologists who first studied them found that most include four categories of information:

• Fault: the pathophysiology that led to the illness.
• Predisposing conditions: the medical issues or social factors that promote or contribute to the disease
• Consequences: the typical signs and symptoms
• Management: how the problem is typically diagnosed and treated

During the interview, experienced clinicians compare a patient’s signs and symptoms with illness scripts for different diseases and those that seem to ‘match’ become part of the differential diagnosis.

Dual process theory & illness scripts

If a patient’s problem is familiar, pattern recognition can lead an illness script to pop up almost automatically from the physician’s memory. If the problem is less familiar, it might take deliberate effort.  Dual process theory explains these two different ways of thinking, which are often referred to as System 1 and System 2.

System 1 is fast, unconscious and makes use of pattern recognition and shortcuts. In day-to-day life, humans rely on it most of the time. System 2 is analytic, intentional and often more accurate, but it takes effort and it is slower. In medicine, System 1 allows clinicians to efficiently match patterns of symptoms with illness scripts. It’s efficient and (for experienced physicians) usually right, but it’s sometimes a little sloppy and can lead to diagnostic errors. System 2 is used for less familiar or higher risk patient presentations. Right now, most of your clinical reasoning will be System 2 thinking – deliberate and effortful. Even when you learn to quickly recognize patterns, though, it will be important to double-check your hypotheses with System 2 to avoid diagnostic errors.

Consciously comparing illness scripts can build your diagnostic skills more quickly. In this workshop, we’ll build, compare and contrast illness scripts for diagnoses that present with sore throat, using what you’ve learned in Infections & Immunity to practice thinking like a doctor!

Example: Problem representation to illness scripts

Imagine you’re seeing a previously healthy 15-year-old in your primary care clinic. The reason for the visit is “2 days of sore throat and fever”. Your problem representation as you walk in the room is “healthy teenager with sore throat and fever”

Based on this limited information, diagnoses are probably already coming to mind. Strep throat is so common that System 1/pattern recognition may have activated this illness script right away. A pediatrician who has seen hundreds of cases of GAS pharyngitis would have a much more detailed script, expanding beyond the ‘classic’ findings to include less common presentations.   Your illness scripts will be richer and more detailed for diseases that you see often.

Most clinical syndromes could be due to several possible diagnoses, and considering them in parallel can prevent diagnostic error and help you build your diagnostic reasoning skills.  Next term, your FCM write-ups will include the illness scripts for 3 or 4 ‘most likely’ and ‘most lethal’ diagnoses on your differential in a table called a diagnoses matrix.

This matrix allows you to explicitly COMPARE and CONTRAST the different potential causes of your patient’s problem, identifying the history, risk factors and exam findings that might help you differentiate between them.  We’ll practice using a diagnosis matrix in the sim.

Knowledge Check

Resources & references

Using script theory to cultivate illness script formation and clinical reasoning in health professions education – PMC (washington.edu)