Case Series

Week 4 -> Dr. Ekong

Case series

A descriptive, observational study that’s used to illustrate an aspect of a condition, treatment or adverse reaction to treatment, in a group of patients with the disease or outcome of interest.

Data from a cluster or series of cases are reported without a comparison group (i.e., no control group); instead, the exposures of the cases are often described.

• e.g., ‘Metoprolol-induced visual hallucinations’

  • 3 patients (case 1, 2, 3) were reporting visual hallucinations

  • After discontinuation of the metoprolol, the visual disturbances resolved within several days

When are case series used?

To describe outcomes of a new treatment

• e.g., “A clinician examines a patient receiving a specific medication who develops a rare side effect to the medication. The clinician will search for cases/patients with similar side effects to the medication and identify patterns.” (this process could help given an intervention/recommendation regarding the direction of treatment or diagnosis)

Descriptive/Qualitative Data

Reports of case series usually contain detailed information about the individual patients

• Demographic information

• Information on diagnosis

• Treatment

• Response to treatment

• Follow-up after treatment

What are the strengths of case series?

• Informs patients and physicians about natural history and prognostic factors

• The information gained from a case series can be used to generate a hypothesis

• It's a feasible study design

  • Easy, inexpensive, and less time-consuming

• Can help answer the question of why this outcome occurred

What are the weaknesses of case series?

• There is no comparison (control) group

  • Selection bias

• Cases may not be representative of the population

• Outcome may be a chance finding, not characteristic of the disease

• Doesn’t have statistical validity

  • No cause-and-effect relationship

How to minimize bias in a case series study design?

• Clear study objective/question

• Well-defined study protocol

• Clear inclusion and exclusion criteria for study participants

• Specified time interval for patient recruitment

• Consecutive patient enrollments

• Clinically relevant outcomes

• Prospective outcome data collection

• High follow-up rate

What are the key similarities/differences between a case series and a case-control study?

• Case series

  • Inexpensive

  • Group of cases (disease); no control group

  • Collection → present

  • Purpose → for generating hypothesis

  • Statistical validity → no !!

• Case-control study

  • Inexpensive

  • One group has disease and the other is disease-free (control group)

  • Collection → past

  • Purpose → for testing hypothesis

  • Statistical validity → measure of disease frequency and risk (odds ratio)