Essential Thrombocytemy

The essential thrombocytemy (TE) is a disease of blood belonging to the syndromes myéloprolifératifs. It is a disease clonale characterized by an excessive production of plate S by the mégacariocytes of osseous marrow. The rate of plates must be higher than 600.000/µl to speak about TE and it is generally higher than 1.000.000/µl.

This excessive rate of plate is often fortuitously discovered during a hematologic examination sytematic. The Middle Age of discovery is 60 years and there is a female prevalence.

There is no pathognomonic sign clinical or biological and the diagnosis is a diagnosis of exclusion with the reactional thrombocytoses or the other chronic syndromes myéloprolifératifs or one finds thrombocytémies.

Clinical symptomatology and the risks of TE are primarily vascular with ischemic transitory demonstrations on the level of the Microcirculation, true especially arterial thromboses and seldom of the hemorrhages.

TE does not modify the life expectancy of the patients.

The therapeutic attitude and the indications depend on the vascular risk and must take into account the iatrogénie certain drugs. The various attitudes go from the abstention with simple monitoring, the use of drugs decreasing the production of plates, a treatment by antoagrégants.

TE belongs to the 4 large syndromes myéloprolifératifs:

the Maladie of Be occupied
the chronic Leucémie myéloïde
the essential Thrombocytémie
the primitive Splénomégalie myéloïde or myélofibrose

Some distinctions

It is necessary to distinguish:

a Hyperplaquettose or Thrombocytose which is an increase in the number of the blood plates > 450 Giga/l.
a Thrombocytémie which is a term applying to the thrombocytoses being integrated within the framework of a myéloprolifératif syndrome.
the term of essential thrombocytemy or primitive which is a particular variety of myéloprolifératif syndrome characterized by a proliferation of the line mégacaryocytaire.

Diagnosis criteria of TE

The TE diagnosis remains a diagnosis of elimination, it does not exist any specific marker. It is necessary to distinguish a TE from a reactional thrombocytose and other SMP when they are accompanied by a hyperplaquettose.

The diagnostic criteria of the Polycythemia Vera Study Group established in 1997

Plates > 600 Giga/l, with two one month successive examinations, separated;
Absence of etiology of thrombocytose secondary reactional to an inflammatory disease, a neoplasic disease, a martial deficiency (normal ferritinemy and normal VGM of red blood corpuscles), a hémolyse or a asplénie.
Presence of a number increased of mégacaryocytes of big size in cluster without anomaly of nucléo-cytoplasmic maturation
Absence of signs cytological or cytogenetic in favor of a syndrome myelodysplasic (presence of colourable iron in marrow but absence of sidéroblastes in crown)
HT < 50% for the men, HT < 45% for the women or if these limits are reached normal isotopic globular volume (< 125% of the normal values calculated)
Absence of Ph1 chromosome or rearrangement bcr-abl ((eliminating the LMC at the time of the medullary chromosomic chart and the cytogenetic study)
Absence of reticulinic medullary fibrosis or marginal increase in the density of fibers of réticuline

The European clinicopathological criteria for the diagnosis of TE

They add the absence of splénomégalie (or minor with echography), the spontaneous formation of colonies mégacaryocytaires (CFU-Meg), and specify the criteria anatomopathologic:

B1 - prevalent Proliferation large mégacaryocytes with hyperlobulé core and mature cytoplasm, without obvious cytological anomaly. In addition, absence of excessive proliferation or immaturity of the granulopoïèse and the érythropoïèse.
B2 - normal or hardly increased reticulinic Screen.

The combination of A1 and B1 + B2 establishes the TE diagnosis. Each additional criterion has consolidates the TE diagnosis.

One also defines the TE as being of rank I if the numeration of the plates is from 400 to 1500 G/l, and of rank II beyond 1500 G/l.

References

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