How to get experience with rare cases in med school

Rare diseases aren’t rare

Orphanet’s database covers 6,172 rare diseases. Each one is uncommon, but a conservative estimate puts the total at 3.5% to 5.9% of the population, or 263 to 446 million people at any moment.¹ Of those diseases, 71.9% are genetic and 69.9% begin only in childhood.

You will meet these patients. You won’t know in advance which disease they have, so learning them one at a time won’t work. Learning to notice the pattern does.

Why the diagnosis takes years

A Rare Barometer survey of 6,507 people across 41 European countries found an average total diagnosis time of 4.7 years.² More than half, 56%, were diagnosed more than six months after their first medical contact. Symptoms that started in childhood or adolescence were linked to longer delays.

Not every delay is avoidable. The part that starts in a consultation, with a history that doesn’t quite fit, is the part you can train for.

Think horses, then check for zebras

“When you hear hoofbeats, think of horses, not zebras” is commonly credited to Theodore Woodward of the University of Maryland School of Medicine, though the evidence for it is indirect.³ It’s good advice for the first guess. The skill is knowing when to stop trusting it:

• The story doesn’t fit the common diagnosis, or the common treatment failed
• Symptoms cross systems that don’t usually go together
• It started young, or runs in the family
• The patient has seen several doctors for the same problem

Any one of these is a reason to ask the question that tests the unlikely answer, not a reason to order every test.

What you can do alone this week

Rare-case exposure doesn’t have to wait for the right placement. Five habits you can start now:

• Read one case report a day in the specialty you’re on. Stop after the presentation, write your differential, then read the rest.
• Keep a personal zebra list: one line per condition and the clue that should have triggered it. Reread it before exams and new placements.
• Drill red flags. Pick one presenting complaint a week and list what would make it dangerous or unusual.
• Ask seniors about the case they nearly missed. You’ll learn the clue, and what it felt like to almost walk past it.
• Take histories from simulated patients with uncommon presentations, so the first strange story you hear isn’t a real one.

Use electives and specialist clinics

If your school allows it, a few days in a genetics, metabolic or pediatric specialty clinic concentrates rare disease in one room. Sit in on multidisciplinary meetings, where unusual cases get argued out loud. Rare disease charities and patient groups run events too, and hearing how someone’s diagnosis was missed sticks longer than any list.

Practice before it counts

Spin the case roulette at the top. Some of the cases in the bank are uncommon presentations, and the room won’t tell you which. Take the history, build your differential, and afterwards you’re marked against 48 criteria, including family history and the systems review.