The medical boards present multiple-choice questions that are fair and clinically relevant with pride. Simply meaning, they are not trying to trick you. Most of the case vignettes present a patient with a common form of the condition or disease, as these common forms are the ones assessed and treated by most physicians. On the other hand, as clinicians, we should be able to recognize rare disorders. Hence, the question is, how do you figure out if the question is about a “horse” or a “zebra”?
When the question is about a “zebra”, usually some information about the patient’s demographics is given in the case vignette which is unusual for that particular disorder, such as the age of occurrence, gender, or the racial or ethnic group may be unusual. For example, on the family medicine boards, a case with classic presentation of acute cholelithiasis in an adolescent who has never been pregnant is described. The age of the patient should prompt you to think about causes common in children and adolescents and not common in adults; for example, in a case with a history of hemolytic disease, formation of black pigment stones can occur. Or, if on the psychiatry board, a 55-year old man with dementia, but no family history of dementia is described, it is highly unlikely that the etiology is Alzheimer’s disease unless the patient has a mosaic form of trisomy 21, which has lower physical evidence of Down Syndrome stigmata. Or, if the clinical vignette describes a young woman of East-Asia presenting to the ER in an unconscious state, it should prompt you to think why her race or ethnicity is given in the vignette. Let’s suppose the vignette describes a family member informing you that she is an immigrant from a rural province in China and that she has been disheartened about her move to the U.S.
The question may be about a “zebra” because it includes an out of place piece of information in the clinical presentation. For instance, a patient presents with a history of nocturnal panic attacks (not uncommon) who also has been prescribed an unnamed medication for anxiety by his primary care physician. The initial thought of the candidate taking the test might be that the current treatment is not working, which may be the case. Alternatively, the patient might be taking a short-acting drug whose effects wear off before the next dose is due. A commonly used drug for nocturnal anxiety or panic disorder is immediate release alprazolam. Even though the FDA approves it for panic disorder, it results in drug-withdrawal anxiety when plasma levels decrease due to its very short half-life. So, if the case vignette is describing the presence of nocturnal attacks along with some medication being taken by the patient, it should trigger you to explore and think about other clinical hypotheses.
Another clue for a “zebra” question is related to the nature of the disorder. The clinical vignette may describe a patient with a recent history of international travel (tropical country), a patient with an unusual hobby such as rock climbing, or a particular occupation is described, especially if a factory or agricultural setting is described. For example, herbicides are readily available organophosphate compounds, and exposure to such compounds is more common in individuals residing in a rural or farming community. Organophosphates are cholinesterase inhibitors, and poisoning with them can result in muscarinic or nicotinic hyperactivity, leading to higher incidences of death due to the failure of the diaphragm to work. In rural China, intentional poisoning is a commonly used method of suicide by women. On the other hand, accidental poisoning is also common. In the previously described scenario about a young East–Asian woman, the information that she comes from a rural community, and her disheartened demeanor, are important clues along with the possibility that she might be aware of the lethality of the commonly available herbicides.
On the board exams, a question does not present any information by accident. All of the pieces of information or facts in the question are designed to help you along a particular diagnostic or treatment path. The information will help you to make a diagnostic and/or treatment distinction.
Example Exam Question from Family Medicine
A 33-year-old lactating mother presents to the clinic with a history of vaginal bleeding for the past three months. She had delivered her second baby six months ago via spontaneous vaginal delivery. She is vitally stable. The laboratory workup reveals a beta hCG of 938,000mIU/mL and positive Anti-HCV. What is the most likely etiology of this patient’s presentation?
- Gestational trophoblastic disease (GTN)
GTN is the correct answer. GTN is the most likely cause because of the presentation of vaginal bleeding in the postpartum period along with elevated levels of beta hCG above normal levels of a pregnant female. GTN usually occurs following a recent antecedent pregnancy, generally within 12 months of the last delivery. GTN includes invasive mole, choriocarcinoma, placental-site trophoblastic tumor, and epithelioid trophoblastic tumor. The patient is a lactating mother, which means it is highly unlikely that she is pregnant or had a miscarriage. Also, beta hCG levels are elevated above the range for a normal pregnancy or miscarriage. Endometritis is incorrect, as it is an infection which usually presents with lower abdominal pain, fever, and heavy vaginal bleeding up to six weeks after delivery and in most of the cases, there is a history of delivery by caesarian section. Hepatitis is unlikely, as there are no associated symptoms that favor an infection with HCV, and the laboratory test for HCV may be due to a previous infection.
Ngan HY, Seckl MJ, Berkowitz RS, Xiang Y, Golfier F, Sekharan PK, Lurain JR. Update on the diagnosis and management of gestational trophoblastic disease. Int J Gynecol Obstet. 2015; 131 Suppl 2:S123-6. DOI: 10.1016/j.ijgo.2015.06.008.
Shaaban AM, Rezvani M1, Haroun RR, Kennedy AM, Elsayes KM, Olpin JD, Salama ME, Foster BR, Menias CO. Gestational Trophoblastic Disease: Clinical and Imaging Features. Radiographics. 2017; 37(2):681-700. DOI: 10.1148/rg.2017160140.