Having looked at the causes of hemolytic anemia in a general way (we grouped them into hereditary and acquired groups, and defined the general clinical characteristics of each), let’s take a closer look at the specific kinds of hemolytic anemia. We’ll discuss the hereditary causes first, starting with hereditary spherocytosis.
Hereditary spherocytosis is a relatively common disorder (as far as hematologic disorders go): 1 in 5,000 people of Northern European descent have it (the incidence is lower in other racial groups). Though it is a hereditary disorder, the age of onset of clinical symptoms – and their severity – is variable. The clinical symptoms are usually described as a triad of mild anemia, intermittent jaundice, and splenomegaly. Most patients are able to make enough new red cells to replace the ones that are being prematurely destroyed – so most of the time, there is a mild anemia (or no anemia at all). It’s when a patient gets exposed to something that is nasty to red cells, like parvovirus B19 infection (which wipes out red cells), that the patient can enter what’s called a “crisis” – meaning that the already maxed-out bone marrow can’t keep up with the newly increased demand, and a sudden worsening of the anemia occurs. In these crises, the patient will likely experience clinical signs of anemia (fatigue, for example) and jaundice (from the increased hemolysis).
The basic defect in hereditary spherocytosis involves spectrin, a component of the membrane cytoskeleton. Either there’s not enough spectrin around, or it doesn’t work properly, leading to membrane instability, and loss of bits of membrane (which means that the cells round up, making spherocytes, which are the darker, smaller red cells with no central pallor in the image above). The big problem in this disorder is that the macrophages in the spleen see these abnormal cells and eat them up! It’s not so much the spherocytes themselves (though they are more fragile than normal biconcave-disc-shaped red cells) – it’s the removal of red cells by the spleen that is the main cause of the anemia.
So when you look at a blood smear of a patient with hereditary spherocytosis, you’ll see spherocytes (you didn’t need me to tell you that). Depending on the severity of the patient’s genetic spectrin abnormality, there may be a few spherocytes, or a ton of spherocytes. You’ll also see evidence of accelerated hematopoiesis in the form of reticulocytosis (actually, you should say “polychromatophilia” if you’re describing a normally-stained blood smear. Reticulocytes are only visible on a supravital stain; on a regular Wright-Giemsa stained blood smear, you call those same cells polychromatophilic cells. You can see a polychromatophilic cell in the image above directly below the center neutrophil. If it were a supravital stain, you’d call that same cell a reticulocyte. But that’s getting a little picky.). If the bone marrow is really cranking out red cells, you might see some nucleated red cells in the blood too.
Therapy for this disorder, if necessary (many patients can get along just fine), involves splenectomy (if the patient can tolerate it). The spleen is the site of destruction of the red cells in hereditary spherocytosis. Remove the spleen, and you remove the place where the cells get destroyed! You’re not curing the genetic defect, of course; the patient will still have some spherocytes in the blood. But you are treating the disease so effectively that the patient should not have any further clinical symptoms. If splenectomy is not an option, then the patient may need red cell transfusions during crises.
Photo credit: Ed Uthman (http://www.flickr.com/photos/euthman/2989437967/).
- Kristine Krafts, M.D. Assistant Professor, Department of Pathology University of Minnesota School of Medicine April 2013: 78,614 unique visitors.
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