Wednesday, September 17, 2008
There has been quite a lot of discussion lately about prolymphocytes. A prolymphocyte is a lymphocyte that looks different down the microscope. It is larger than the average lymphocyte, the nucleus tends to be a bit eccentric in the cytoplasm (as in off-center not as in crazy). The nucleus has a single prominent nucleolus and the cytoplasm may stain a bit bluish. These are not blast cells; they are probably lymphocytes that have been activated, but not very much. There are a couple of types of leukemia that consist entirely of prolymphocytes (T-PLL and B-PLL) and I have written about them before here .
When prolymphocytes appear in the blood of patients with CLL, people get worried that the disease is transforming. If you follow the link you will find that this is usually not so. For one thing, prolymphocytes are often missed on the blood film if the spreading is not good enough or the staining poor. If you have trisomy 12 then to have 10-15% prolymphocytes is quite normal. They appear after you flu jab and if you have an infection. Furthermore, CLL does not transform into PLL as some of the older specialists thought. B-PLL is a quite separate (and very rare) disease.
Another important point is about calculating the absolute lymphocyte count. The prolymphocytes should be counted in with the lymphocytes (so should the atypical lymphocytes). I have been asked by worried patients about a change in their absolute lymphocyte count because the first lab did not include them and the second one did.