OSU logo Oklahoma State University
Center for Health Sciences
Medical Physiology - Evidence-Based Medicine
Printer Friendly


What is EBM?

Patient Care Model
Life-long Learning
Why is EBM Important?
Available Evidence?
EBM Issues

The Well-built Question

The EBM Process
Anatomy of a Question

Finding Evidence

Selecting a Resource
Searching the Resource
Reviewing Search Results
Returning to the Patient

Evaluating Evidence

Evaluating the Validity
Validity Questions


Knowledge Test

Multiple Sclerosis
Case #2
Case #3
Case #4




In the following exercise, click an answer and a pop-up box will appear that contains feedback.

Note: If you do not see a pop-up box, check your popup blocker settings in the browser. If that is not the problem, try closing the previous pop-up box or check to see if the pop-up box is behind your browser window.  If you still do not see the pop-up box, you may need to update your browser.

Case 2: Myasthenia Gravis

The Patient

1. Start with the patient - a clinical problem or question arises out of the care of the patient.

A 25-year-old right-handed woman develops intermittent diplopia and variable bilateral ptosis. An initial examination shows negative results. Two months later she develops persistent diplopia, which varies in degree, right ptosis, and difficulty climbing stairs as well as slurred speech when speaking for several minutes that improves with rest. Her examination shows right ptosis, variable external ophthalmoparesis (pupil is spared), dysarthria when counting to one hundred, difficulty doing deep knee bends. Her mental status, sensory and reflex examinations are normal. Her anti-AChR antibodies are increased and repetitive nerve stimulation test is positive for myasthenia gravis . CT scan of the chest is normal. She is treated with pyridostigmine 60 mg po q4h with reduction in all of her symptoms. After 6 months she still has intermittent diplopia and has developed some difficulty getting up from a low chair, particularly late in the day. Serum TSH and free T 4 levels are normal.

Following the recommendation of her neurologist, the patient undergoes an external transsternal thymectomy with no complications. Her symptoms persist unchanged for approximately 6 months and then begin to subside. Two years after thymectomy she is asymptomatic. On examination she has minor intermittently inducible ptosis on the right.

The patient's insurance company has refused to pay for the thymectomy, claiming that procedure is not supported by evidence in the medical literature as an effective treatment for myasthenia gravis. An intern working with the patient's neurologist is tasked with finding the evidence to justify the thymectomy.

The Question

2. Construct a well-built clinical question derived from the case.

Based on this scenario, choose the best, well-built clinical question:

A. For an adult female diagnosed with myasthenia gravis is thymectomy a reasonable treatment to achieve a significant reduction in her symptoms?

B. For a patient diagnosed with myasthenia gravis can surgery be beneficial?

C. For an adult female with myasthenia gravis will her insurance company pay for thymectomy?

The Resource

3. Launch FIRSTConsult and conduct a search using the well-built question from Answer A above. (Hint: In point-of-care databases it is best to start by searching for the pre-dominant medical condition, in this case "myasthenia gravis.")

Based on your DynaMed search results please answer the following question.

Where is thymectomy placed in the "Order of therapies" given by FIRSTConsult?

A. First

B. Fourth

C. Third

The Evaluation

4. Appraise the evidence for its validity (closeness to the truth) and its applicability (usefulness in clinical practice).

As stated previously, evaluating medical research reports is a complex and time-consuming undertaking. The best resources in the clinical setting are the point-of-care databases which provide pre-evaluated answers to specific clinical questions in the practical time frame needed by a practicing physician.

FIRSTConsult is a good example of a database providing patient-oriented, evidence-based clinical answers that are pre-evaluated for validity. Evidence in FIRSTConsult is labeled in one of three levels so clinicians can quickly grasp the reliability of conclusions and recommendations.")'>

Based on your FIRSTConsult search results please answer the following question.

In FIRSTConsult what level of evidence is assigned to thymectomy as a treatment for reducing symptoms caused by myasthenia gravis?

A. Level A [good-to-high quality RCTs]

B. Level B [mid-range quality RCTs]

C. Level C [expert opinion/consensus statements]

We now go to the Knowledge Test: Case No. 3.