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New diagnostic criteria-ET
Subject: ET criteria from reactive thrombocytosis (secondary)
Helen,
No, Norm has never had platelets above 400,000 - polycythemia vera as a
myeloproliferative disease is characterized by the proliferation (or
accumulation!) of erythrocytes (red blood cells), while essential
thrombocythemia is considered to be a myeloproliferative disease
characterized by proliferation of the platelets (thrombocytes, earlier
forms - megakaryocytes). A high platelet count is used as one of the minor
criteria for diagnosing PV, but it is not a major criteria. On the other
hand, high platelets is a major criteria of ET. I have a number of article
references that indicate a bone marrow biopsy is not all that helpful in
distinguishing the difference between ET and PV. I know that you saw the
earlier posting I sent on some "updated" criteria for diagnosing PV; I will
repost it today for others that might be interested.
Below is a brief summary of a similar article detailing criteria to
distinguish ET from secondary (reactive) thrombocytosis. It also comes
from LEUKEMIA AND LYMPHOMA, vol. 22, suppl. 1, 1996, by Kutti & Wadenvik,
entitled, "Diagnostic and differential criteria of essential
thrombocythemia and reactive thrombocytosis." AND below that I'll include
an updated version of the Polycythemia Vera Study Group (PVSG) criteria for
ET.
"Major" criteria: 1. Platelet count in excess of 600 x 10 (9)/L
2. No increased red cell mass in the presence of stainable iron in the
bone marrow OR failure of iron trial. ((To explain this a bit - red cell
mass-RCM- is considered increased by "older" method if above 36 mL/kg in
males or above 32 mL/kg in females. "Newer" method if above 25% of the
mean normal predicted value for that individual. AND earlier PVSG
guidelines would have said that normal marrow iron stores meant ET, absence
meant PV - I am simplifying here a bit - but it is now recognized that ET
and reactive thrombocytosis (due to iron deficiency) can have absence of
iron stores - hence the iron trial - give iron and see if RCM increases.))
3. No Philadelphia chromosome
4. Megakaryocytic hyperplasia (increased size & number) with no collagen
fibrosis in bone marrow
"Minor" criteria: 1. Splenomegaly
2. Growth of BFU-E or CFU-Meg (This is similar to the endogenous
erythroid colony test that we've talked about.)
3. Normal ESR/fibrinogen (dealing with platelet function tests)
The diagnosis of ET is said to be established if either all 4 of the major
criteria are met, or the first 3 of the major criteria and 2 of the minor
criteria. Remembering that the point of this article was to establish
criteria between ET and reactive (secondary) thrombocytosis. Below is an
updated set of diagnositic criteria from the PVSG.
1. Platelet count in excess of 600,000/uL
2. Hematocrit below 40 OR normal red cell mass
3. Stainable iron in the marrow OR normal serum (blood) ferritin OR
normal MCV (mean corpuscular volume)
4. No Philadelphia chromosome OR bcr/abl gene rearrangement (to rule out
CML).
5. Collagen fibrosis of marrow absent OR, if present, less than 1/3 of
biopsy area and NO corresponding splenomegaly and/or leukoerythroblastic
blood picture (This deals with abnormal platelets, immature red & white
blood cells, and tear-drop red blood cells in the peripheral blood -
presence of would be indicator of MF, not ET for diagnosis.)
6. No cytogenetic or morphologic evidence (abnormal chromosomes, blood)
for MDS- myelodysplastic syndrome
7. No cause for reactive thrombocytosis
And that list seems to cover just about everything! Of course, difficulty
comes, for example, when patient has been phlebotomized, etc., before red
cell mass study or iron trial - when platelets high, but perhaps hematocrit
not so much so. There are a number of articles that go into this a bit -
some algorithms that may be used in such cases to determine PV or ET. I
think (just personal opinion here) that some hematologists don't think it
is all that important to get the diagnosis correct (not all that long ago
there was debate on whether ET and PV ARE separate diseases - perhaps some
would still debate this). I can understand this to a degree - in some cases
it may not make any difference in treatment, and, in these cases, it may
not be important.
There ARE other times when it really may matter in respect to treatment -
some would not see a routine progression of ET to end-stage MF, for
example. This can make a difference in whether to treat with something
other than phlebotomy if the diagnosis is really PV, not ET (or vice versa).
In another aspect, those ET confirmed by positive EEC (or newer BFU) or
CFU-meg, may face a greater risk of thrombotic events (as well those PV
confirmed by the same tests) so, again, this could make a difference in
deciding whether to treat or not to treat high platelets with some sort of
myelosuppressive.
And yet another aspect may well be when platelets rise later in the course
of PV - this may be (as indicated in some articles) a time to look
seriously at myelosuppression to halt progression to spent phase - if the
only previous treatment has been phlebotomy. ((A warning that in some cases
as per some articles, it has not been soon enough to halt spent; for that
matter, as in Norm's case (my husband) the elevated platelet levels never
came - but abnormal mekaryopoiesis (platelet production) is there without
the indicator of high platelets.))