when you hear hoofbeats...

It's an oft repeated axiom of medicine.  If you hear hoofbeats, think horse, not zebra.  It means the common things happen commonly.  Don't go looking for exotic stuff.  But we're also supposed to keep an open mind as to the possibilities.  How in the world to does one test that?  I don't do as well on standardized tests as I'd like.  I think I'm too used to looking for zebras.  In my prior career, we set out to look for the new, the novel, the (hopefully) revolutionary ways of treating a disease.  I saw parts of physiology that no one else in the world knew.  Fast forward to my brief medical career and my family.  My brother?  Thymic cancer.  That's not even a zebra.  That's beyond zebra.  My dad?  CLL, well that's common.  Except his was highly aggressive.  Everything I've learned from recent lectures has been that CLL is slow and not that big of a deal.  One lecture over the pathology of it had a whopping 122 words over it.  Basically, it's a low-grade disease that's discovered incidentally.  That's it.

A case from a lecture that highlights how slow it is.  This patient has had it for over seven years.  Skip past all this if you're not into all the medical mumbo jumbo.

A 54 yr-old woman presents to your office with fever and persistent bleeding from a dental extraction done 3 weeks ago.  The patient has felt well for the past month with no fevers or weight loss, but she has had some fatigue that she attributes to long hours at work.  Seven years ago she was noted to be pancytopenic and was diagnosed with aplastic anemia.  She was treated with antithymocyte globulin, cyclosporine, and prednisone and had a complete hematologic recovery.

Physical examination shows a pale, middle-aged woman.  There is no lympadenopathy or hepatosplenomegaly.

  Laboratory studies:

  Hemoglobin  8.2 g/dl

  Mean corpuscular volume  117fL

  Leukocyte count  3100μL

–Segmented neutrophils  21%

–Band forms  10%

–Lymphocytes  68%

–Monocytes  1%

  Platelet count  36,000/μL

Peripheral blood morphology shows hypogranular and hyposegmented neutrophils.  The erythrocyte morphology shows both anisocytosis and poikilocytosis with some teardrop cells.

 What is the most likely diagnosis?

a) recurrent aplastic anemia
b) chronic lymphocytic leukemia
c) myelodysplasia
d) B12 deficiency
e) Miliary tuberculosis