Case Reports and Case Series

Case reports are the oldest form of medical literature, dating back centuries. They document novel diseases (the first HIV cases in 1981 were case reports published in the MMWR), rare adverse drug reactions, unexpected treatment responses, or unusual presentations of common diseases. A single case report describes one patient in detail: presentation, workup, diagnosis, treatment, and outcome. A case series extends this by collecting multiple similar cases (typically 3 or more), allowing patterns to emerge. Neither design has a comparison group, so they cannot establish causation, measure effect sizes, or calculate risk. However, they serve critical functions in medicine: they generate hypotheses that larger studies can test, they document the first occurrence of new diseases or complications, and they report on rare conditions where larger studies are impossible. There are several types of case reports to know. A diagnostic case report describes an unusual or challenging diagnostic process. A treatment case report documents a novel or unexpected therapeutic approach. An adverse event case report describes an unexpected harm from a drug or procedure. An educational case report is structured primarily to teach a clinical lesson. Case reports remain the first step for reporting rare events, novel therapies, and diagnostic challenges. Most journals accept them, and they count toward a researcher's publication record — making them an excellent starting point for residents and junior faculty. The CARE (CAse REport) guideline provides a structured 13-item checklist to ensure complete and transparent reporting. Key items include a clear timeline, diagnostic reasoning, therapeutic interventions with dosing, patient perspective when possible, and an informed consent statement. In later levels of this course, you will learn how to conduct each of these study designs step by step from zero — from writing the protocol to collecting data to analyzing results and writing the manuscript.