Syllabi - Geriatric Medicine - Prognosis Scenario

You see a 70 year old man in an outpatient clinical 3 months after he has been discharged from your service with an ischaemic (presumed thrombotic) stroke. He is in sinus rhythm, has mild residual left-sided weakness but is otherwise well. His only medication is aspirin and he has no allergies. He recently saw an article on the BMJ website describing the risk of seizure after a stroke and is concerned that this will happen to him. Together you form the question: "In patients with a history of stroke, what is the risk of seizure within the first year?"

You search MEDLINE using the terms "stroke" and "seizure" and find the article he was referring to. BMJ 1997;315:1582-7

Read the article and decide:

Is this evidence about prognosis valid?
Is this valid evidence about prognosis important?
Can you apply this valid and important evidence about prognosis in caring for your patient?

Completed Prognosis Worksheet for Evidence-Based Geriatric Medicine

Citation

Burn J, Dennis M, Bamford J et al. Epileptic seizures after a first stroke: the Oxfordshire community stroke project.
BMJ 1997;315:1582-7

Are the results of this prognosis study valid?

Was a defined, representative sample of patients assembled at a common (usually early) point in the course of their disease?: Yes - from a common point but unsure how GPs decided which stroke patients should be admitted to hospital
Was patient follow-up sufficiently long and complete?: Yes-minimum of 2 years and up to 6.5 years
Were objective outcome criteria applied in a "blind" fashion?: Patients were asked at follow-up if they had a seizure and were then assessed by a study neurologist (unsure if neurologist was blinded)
If subgroups with different prognoses are identified, was there adjustment for important prognostic factors?: Looked at different stroke types, previous history of stroke
Was there validation in an independent group ("test-set") of patients?: No

Are the valid results of this prognosis study important?

How likely are the outcomes over time?: 5.7% over one year
How precise are the prognostic estimates?: 95% confidence interval - 3.5 to 7.9%

If you want to calculate a Confidence Interval around the measure of Prognosis

Clinical Measure	Standard Error (SE)	Typical calculation of CI
Proportion (as in the rate of some prognostic event, etc) where: the number of patients = n the proportion of these patients who experience the event = p	sqrt((px(1-p))/n) where p is proportion and n is number of patients	If p = 24/60 = 0.4 (or 40%) and n=60 sqrt((0.4x(1-0.4))/60) = 0.063 (or 6.3%) 95% CI is 40% +/- 1.96 x 6.3% or 27.6% to 52.4%
n from your evidence: 675 p from your evidence: 0.057	sqrt((px(1-p))/n) where p is proportion and n is number of patients	Your calculation: SE = 0.009 95% CI: 5.7% ± 1.7% = 4% to 7.4%

Clinical Measure

Standard Error (SE)

Typical calculation of CI

Proportion (as in the rate of some prognostic event, etc) where:
the number of patients = n
the proportion of these patients who experience the event = p

sqrt((px(1-p))/n)
where p is proportion and n is number of patients

If p = 24/60 = 0.4 (or 40%) and n=60
sqrt((0.4x(1-0.4))/60)
= 0.063 (or 6.3%)

95% CI is 40% +/- 1.96 x 6.3% or 27.6% to 52.4%

n from your evidence: 675
p from your evidence: 0.057

sqrt((px(1-p))/n)
where p is proportion and n is number of patients

Your calculation:
SE = 0.009
95% CI: 5.7% ± 1.7% = 4% to 7.4%

Can you apply this valid, important evidence about prognosis in caring for your patient?

Were the study patients similar to your own?: Yes
Will this evidence make a clinically important impact on your conclusions about what to offer or tell your patient?: Yes

Additional Notes

Stroke-risk of seizure

Clinical Bottom Line

Acute Cholecystitis - Lap chole may be as safe as open chole

Citation

Burn J, Dennis M, Bamford J et al. Epileptic seizures after a first stroke: the Oxfordshire community stroke project. BMJ 1997;315:1582-7

Clinical Question

In a patient with stroke, what is the risk of seizure at one year?

Search Terms

"stroke" and "seizure" in Medline

The Study

675 pts registered in a community-based stroke registry after their first stroke
The Outcome: seizure
Well-defined sample at uniform (early) stage of illness..?, yes;
Follow-up long enough..?, yes;
Follow-up complete..?, yes;
Blind and objective outcome criteria..?, no;
Adjustment for other prognostic factors..?, no;
Validation in an independent "test-set" of patients..?, no

The Evidence

Prognostic Factor	Outcome	Time	Measure	Likelihood Ratio
cerebral infarction	seizure	1 year	4.2%	2.2 to 6.2%
primary intracerebral haemorrhage	seizure	1 year	20%	1.5 to 38.3%
subarachnoid haemorrhage	seizure	1 year	22%	2.6 to 41.8%
any stroke	seizure	1 year	5.7%	3.5 to 7.9%

Appraised By

Straus