USMLE® Step 1 style questions USMLE
A 51-year-old woman comes to the office because of new fatigue and shortness of breath for a month. She has a history of breast cancer which was successfully treated with surgery, chemotherapy, and radiotherapy. Complete blood count shows a pancytopenia (decreased RBCs, WBCs, and platelets). A bone marrow biopsy shows hypercellular marrow. Which of the following is the most likely diagnosis?
MDS can affect individuals of all ages, but it’s more common after the age of 60.
Blood cells develop from hematopoietic stem cells, through a process called hematopoiesis.
This involves a number of divisions, and eventually, results in three types of blood cells: red blood cells, which carry oxygen around our bodies, white blood cells to help fight disease causing pathogens, and platelets that help form clots to stop bleeding.
Once these cells are fully mature, they leave the bone marrow and enter the bloodstream.
In MDS, hematopoietic stem cells are damaged, so they give rise to faulty blood cells, which don’t mature, but instead persist as immature cells, called blasts.
These immature blood cells usually die in the bone marrow or soon after they go into the blood, so you can’t really count on them to do the job of mature blood cells.
As the condition progresses, immature blood cells gradually take over the bone marrow, which displaces and reduces the normal ones.
In most cases, the cause of MDS is not known.
When this happens, it's classified as primary MDS.
In rare cases, they can be caused by chemo or radiation therapy, and this is called secondary MDS.
MDS comprises a spectrum of diseases with differing potential for remaining stable or progressing to acute myeloid leukemia, or AML.
The most common feature of MDS is anemia, caused by low red blood cell levels.
Symptoms of anemia include dizziness, irritability, headaches, and pale skin.
Low white blood cell levels increase the risk of bacterial and fungal infections.
Finally, low levels of platelets cause excessive bruising following minimal injury and easy bleeding.
Now, MDS usually worsens with time, as normal bone marrow function diminishes.
40-50 percent of the time, MDS deteriorates into a form of cancer known as acute myeloid leukemia, or AML.
This happens when there are more than 20% blasts in the bone marrow.
Diagnosis requires a variety of specialized tests including complete blood counts, a peripheral blood smear, as well as bone marrow aspiration and biopsy.
On a complete blood count, there may be low levels of one, two or all of the three blood cell types.
On a peripheral blood smear, there may be big and oval-shaped red blood cells and abnormal white blood cells and platelets.
The bone marrow sample may show an increase in cell count with dysplastic changes in the three blood cell types.