This is the lecture notes for Case study and case series (HFS3063)

1. KNOWLEDGE FOR THE BENEFIT OF HUMANITYKNOWLEDGE FOR THE BENEFIT OF HUMANITY
PUBLIC HEALTH AND EPIDEMIOLOGY (HFS3063)
Epidemiological Study Designs:
CASE STUDY, CASE SERIES
Dr.Dr. MohdMohd RazifRazif ShahrilShahril
School of Nutrition & DieteticsSchool of Nutrition & Dietetics
Faculty of Health SciencesFaculty of Health Sciences
UniversitiUniversiti SultanSultan ZainalZainal AbidinAbidin
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2. Topic Learning Outcomes
By the end of this lecture, students should be able to;
• describe case study and case series study design.
• explain the advantages and disadvantages of case
study and case series design.
• differentiate case series with cohort study design
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3. Case study
• Detailed presentation of a single case or handful of
cases
• Generally report a new or unique finding e.g.:
– previous undescribed disease
– unexpected link between diseases
– unexpected new therapeutic effect
– adverse events
• The case may be an individual, an event, a policy, etc
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4. 4
Case reports in the larger scheme of things

5. Case studies and reports are low on the totem pole
• Preliminary observations are frequently later
refuted
• May rationalize questionable treatments
– e.g., glycemic index diet vs. carbs counting among
gestational diabetes patient
• Biased reporting
– Negative studies may not be published
• Not experimental
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6. When the gold standard loses its luster
• RCTs are hard and expensive to carry out!
• Difficult to design an effective placebo
• Treatment by nature involves multiple components
• Difficulty blinding participants
– e.g., manipulation vs. massage
• Everyone knows if they receive placebo
– Randomization flaws
• Recruiting patients from advertisements
– Non-equivalent groups
• Ethics involved in giving patients a placebo
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7. Enter the lowly case report
• Not a clinical study per se, but high in clinical
relevance
• Well-done case reports may offer more than
lousy clinical trials
– In judging a prize fight, how to compare 300 light
punches with 200 direct hits?
• May lead to clinical studies
• In rare or new pathologies, may be first evidence
– e.g., Thalidomide and birth defects, toxic shock
syndrome, Lyme disease
• 20-30% of medical articles involve < 10 patients
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8. Research value of case report
• Illustrate or support a hypothesis
– Atlas subluxation in a man with gastritis
• Prompt a new hypothesis
– Atlas subluxation can cause gastritis
• Report treatment failures
– Correcting atlas did not relieve gastritis
• Report iatrogenic reactions
– Gastritis better, but pt. developed brain tumor!
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9. A case report is…
• “Biomedical story-telling” (Lawrence, 1991)
• A delivery vehicle for clinical education; indeed,
“the case must have educational value”
(Lawrence, 1991)
• A stimulant for more comprehensive and
prospective research
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10. A case report is not…
• An anecdote
– Def. - unpublished narrative
• A testimonial
• An advertisement
• “Persuasive communication” (Keating)
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11. Selecting a case
• Case should illustrate an important point
regarding case management (i.e., examination,
evaluation, intervention, outcome).
• Case does not have to have a positive outcome
• Case does not have to be unusual or unique
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12. Sample case reports classified
• Spinal manipulative treatment for 12 pregnant LBP
patients [Clinical Education]
• Brucellosis: a rare cause of the unstable spine [clever
chap]
• RA: a case report [novel treatment]
• Grand Rounds discussion: patient with acute LBP
[Grand Rounds]
• Rotary manipulation for cervical radiculopathy
[unexpected association]
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13. cont. Sample case reports classified
• Mixed sacral fracture before chiropractic adjustment
[unexpected outcome]
• Membranous glomerulonephropathy associated with MS
[unexpected occurrence]
• Post-myelographic cauda equina in young acromegalic
[unique case]
• Arthritis and acetyl myristoleate [glorified advertisement]
• Autism and chronic otitis media [anecdotal]
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14. Case series
• Experience of a group of patients with a similar
diagnosis
• Assesses prevalent disease
• Cases may be identified from a single or multiple
sources
• Generally report on new/unique condition
• A realistic design for rare disorders
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15. (cont.) Case series
• Variation on the theme of the solitary case report
• Retrospective look at series of cases that have features
in common
• Common diagnosis, treatment, measures
– In the literature already
• Each case may be separately described, or the cases
may be lumped together with data summaries
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16. (cont.) Case series
Advantages
• Useful for hypothesis generation
• Informative for very rare disease with few established
risk factors
• Characterizes averages for disorder
Disadvantages
• Cannot study cause and effect relationships
• Cannot assess disease frequency
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17. Cohort study vs. case series
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COHORT STUDY CASE SERIES
• Patients are sampled on the basis of
exposure.
• Information about baseline characteristics
is obtained, and the occurrence of
outcomes is assessed during a specified
follow-up period.
• At baseline, all exposed or unexposed
persons or both may be included.
• Exposure can be a risk factor (such as
smoking), a disease (such as diabetes
mellitus), or an intervention (such as hip
replacement).
• In principle, a cohort study enables
calculation of an absolute risk (or rate) for
the outcome, given a particular exposure.
If a comparison group is included, a
relative risk can also be calculated.
Patients with a particular disease or disease-related
outcome are sampled. Case series exist in 2 types:
1. Sampling is based on a specific outcome and
presence of a specific exposure. Cases are
selected on the basis of a striking association
between exposure and outcome. This type of
case series can be formally thought of as
describing 1 cell (the exposed cases) in an
epidemiologic 2 x 2 table.
2. Selection is based only on a specific outcome,
and data are collected on previous exposures.
Cases are reported regardless of whether they
have specific exposures. This type of case series
can be seen as the case group from a case–
control study or as 2 cells (the exposed and
unexposed cases) from an epidemiologic 2 x 2
table.
The risk for the outcome, given the exposure, cannot
be calculated from either type of case series.
Source: Dekkers et al. (2012)

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19. Test: Case series or cohort study?
SCENARIO 1
• A surgeon performs a new procedure for a life-
threatening condition on 20 patients. Ten
patients survive. Two possible papers can be
considered:
• 1A. A description of all treated patients and
follow-up, with calculation of mortality risk. No
comparison group is included.
• 1B. The same as 1A, except that the treated
group is compared with a historical group from
the same institution to compare mortality risk.
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20. Test: Case series or cohort study?
SCENARIO 1
• A surgeon performs a new procedure for a life-
threatening condition on 20 patients. Ten
patients survive. Two possible papers can be
considered:
• 1A. A description of all treated patients and
follow-up, with calculation of mortality risk. No
comparison group is included (COHORT STUDY)
• 1B. The same as 1A, except that the treated
group is compared with a historical group from
the same institution to compare mortality risk
(COHORT STUDY)
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21. Test: Case series or cohort study?
SCENARIO 2
• Data were collected on patients who had bone marrow
depression at 1 hospital. Potential risk factors, including
drugs known to induce bone marrow depression, were
assessed for all patients. The investigators assessed
whether bone marrow depression was still present after 1
year among patients who received 1 of 2 drugs used to
treat the same disease. Two papers can be written on the
basis of these data:
• 2A. A description of all patients with bone marrow
depression and the frequency of potential risk factors for
bone marrow depression
• 2B. A comparison of the risk for persistent bone marrow
depression after 1 year, for either drug, with calculation of
the absolute and relative risks for persistence
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22. Test: Case series or cohort study?
SCENARIO 2
• Data were collected on patients who had bone marrow
depression at 1 hospital. Potential risk factors, including
drugs known to induce bone marrow depression, were
assessed for all patients. The investigators assessed
whether bone marrow depression was still present after 1
year among patients who received 1 of 2 drugs used to
treat the same disease. Two papers can be written on the
basis of these data:
• 2A. A description of all patients with bone marrow
depression and the frequency of potential risk factors for
bone marrow depression (CASE SERIES)
• 2B. A comparison of the risk for persistent bone marrow
depression after 1 year, for either drug, with calculation of
the absolute and relative risks for persistence (COHORT
STUDY) 22

23. Test: Case series or cohort study?
SCENARIO 3
• In 1 hospital, a subset of patients hospitalized
with Escherichia coli–induced hemolytic–uremic
syndrome (HUS) developed neurologic symptoms
during their stay. Demographic and clinical
characteristics of patients with HUS were
collected. Two papers can be considered:
• 3A. A description of only patients who had HUS
and neurologic symptoms
• 3B. A comparison to assess whether the risk for
neurologic symptoms was higher in male than in
female patients with HUS
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24. Test: Case series or cohort study?
SCENARIO 3
• In 1 hospital, a subset of patients hospitalized
with Escherichia coli–induced hemolytic–uremic
syndrome (HUS) developed neurologic symptoms
during their stay. Demographic and clinical
characteristics of patients with HUS were
collected. Two papers can be considered:
• 3A. A description of only patients who had HUS
and neurologic symptoms (CASE SERIES)
• 3B. A comparison to assess whether the risk for
neurologic symptoms was higher in male than in
female patients with HUS (COHORT STUDY)
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25. Thank YouThank You
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