Illness Scripts

Introduction

An illness script is an organized mental summary of a provider’s knowledge of a disease (1-3). It represents a clinician’s knowledge about a particular disease, and may be as short as a 3×5 pocket card description for a rare disease, or as long as a book chapter for a commonly encountered illness. Classically, the components of a thorough illness script fall into three main categories: “the predisposing conditions, the pathophysiological insult, and the clinical consequences” (4). Within these categories, illness scripts often include a disease’s pathophysiology, epidemiology, time course, salient symptoms and signs, diagnostics, and treatment. For example, a provider’s illness script for community acquired pneumonia (CAP) may include:

  • Infection of the lower respiratory tract
  • Most commonly caused by Streptococcus pneumoniae
Increased risk with:
  • Age
  • Post upper respiratory tract viral infection
  • Structural lung disease
  • Immunodeficiency
  • Acute (days)
  • Progressively worsens if not treated
  • Fever
  • Cough
  • Shortness of breath
  • Tachycardia
  • Tachypnea
  • Hypoxemia
Labs and imaging:
  • Leukocytosis
  • Lobar infiltrate on chest x-ray
  • Bacteria in sputum or blood cultures
  • Antibiotics typically lead to improvement over days

Building Illness Scripts

With experience, providers hone their illness scripts in three important ways (5). 
The absence of a fever does not exclude the diagnosis of CAP in an elderly patient

Encode Predictive Values

Clinicians encode a predictive value for each feature of the disease, enabling them to estimate the likelihood of a diagnosis when that feature is present or absent.

A lobar infiltrate on chest x-ray without cardiomegaly or cephalization of vessels is highly suggestive of CAP and makes congestive heart failure less likely.

Emphasize Distinguishing Features

Clinicians emphasize distinguishing features whose presence or absence significantly alters the likelihood of the diagnosis, and helps differentiate it from another related diagnosis.

Chronic obstructive pulmonary disease (COPD) exacerbation and congestive heart failure resemble CAP.

Consider Disease Mimics

Clinicians develop a list of disease mimickers to consider when an illness script of a particular diagnosis is invoked.

This iterative process is continued throughout a clinician’s career, adds depth, precision and differentiating power to the foundational scripts developed during training (5). Diseases encountered less frequently will have less robust scripts.