Differential diagnosis narrowing is the structured clinical reasoning process by which the NP systematically reduces a broad list of possible diagnoses to the most likely working diagnosis through iterative hypothesis testing. This process integrates history, physical examination, and targeted diagnostic testing in a logical sequence. The process begins with problem representation: distilling the patient's presentation into a concise semantic summary that activates illness scripts. For example, 'a 65-year-old male smoker with acute-onset crushing substernal chest pain radiating to the left arm with diaphoresis' immediately activates scripts for ACS, PE, aortic dissection, and other life-threatening causes. Differential generation uses systematic frameworks: - VINDICATE: Vascular, Inflammatory/Infectious, Neoplastic, Degenerative, Iatrogenic/Intoxication, Congenital, Autoimmune, Traumatic, Endocrine/Metabolic - Anatomical approach: consider structures in the affected region (chest pain → cardiac, pulmonary, esophageal, musculoskeletal, aortic, mediastinal) - Epidemiological approach: common diagnoses first, modulated by patient demographics (age, sex, risk factors) Narrowing strategies: 1. Must-not-miss diagnoses first: always rule out life-threatening conditions before pursuing benign diagnoses (chest pain: rule out ACS, PE, dissection, tension pneumothorax, esophageal rupture BEFORE considering GERD or MSK pain) 2. Pivotal findings: identify history/exam...