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Writer's pictureKatie Berlin

Thrombocytosis

Dr. Moths gave a great noon report of a younger patient without significant past medical history who initially presented in septic shock and developed thrombocytosis.


What is thrombocytosis?

Thrombocytosis is defined as a platelet count about 350-450 K. Thrombocytosis can either be a primary or secondary process.


What is reactive thrombocytosis?

Thrombocytosis caused by a secondary process is known as reactive thrombocytosis.

There is an extensive list of causes of reactive thrombocytosis (taken from UptoDate):

-Nonmalignant hematologic conditions

  • Acute blood loss

  • Acute hemolytic anemia

  • Iron deficiency anemia

  • Treatment of vitamin B12 deficiency

  • Rebound effect after treatment of ITP or ethanol-induced thrombocytopenia

-Nonhematologic Malignant conditions

  • Metastatic cancer

  • Lymphoma

  • Rebound effect following use of myelosuppressive agents

-Acute and chronic inflammatory conditions

  • Rheumatologic disorders, vasculitides

  • Inflammatory bowel disease

  • Celiac disease

  • Kawasaki disease

  • Nephrotic syndrome

  • POEMS syndrome (osteosclerotic myeloma)

-Tissue damage

  • Thermal burns

  • MI

  • Severe trauma

  • Acute pancreatitis

  • Post-surgical period, especially post-splenectomy

-Infections

  • Chronic infections

  • Tuberculosis

  • Acute bacterial and viral infections

-Exercise

-Allergic reactions

-Functional and surgical asplenia

-Reaction to medications

  • Vincristine

  • Epinephrine, glucocorticoids

  • Interleukin-1B

  • All-trans retinoic acid

  • Thrombopoietin, thrombopoietin receptor agonists

Notice that inflammation is a common theme: inflammation is the most common cause for secondary thrombocytosis because a multitude of inflammatory cytokines augment platelet production and release from megakaryocytes.


What about primary thrombocytosis?

Primary thrombocytosis can be familial or secondary to clonal proliferation. We will review Essential Thrombocytosis (ET) here.


ET can be suspected when a patient has a platelet count of at least 600,000 on two occasions separated by at least one month without any secondary causes present.


Patients are generally asymptomatic, but can present with thrombotic events which primarily are arterial (i.e. CVA/TIA, MI, digital ischemia). Patients can also present with erythromelalgia. Finally, bleeding may be seen, either from dysfunctional platelets or from acquired VonWillebrand Disease.


How do I work up a patient with persistent thrombocytosis?



A peripheral blood smear is always a good place to start. If there are worrisome findings, get hematology involved immediately.


Next, evaluate the patient for findings suggestive of a myeloproliferative neoplasm. Suggestive symptoms include vasomotor or constitutional symptoms, unusual clots, or the presence of splenomegaly on examination. Jump right to evaluation of a MPN (discussed below) if these are present.


If none of these are present, check a ferritin. If low, replete the patient's iron deficiency and recheck the platelet count in 1-2 months. If still elevated, hematology should be involved. If normal or high, look for a family history (if present, send to hematology) or evidence of infection, inflammation, or a splenectomy. If the latter are present, you can try treating. If unsure, send to hematology.


What do I do if I suspect a myeloproliferative neoplasm (MPN), specifically ET?

Molecular diagnostics are the first test of choice. Screen with JAK2 testing first, as 50% of cases of ET have a positive mutation.


Next, get a BCR-ABL, MPL + CAL-R if JAK2 negative. (Remember that CML can present with isolated thrombocytosis). After this, additional testing including FISH and bone marrow biopsy may be needed.


There are specific diagnostic criteria for ET. Of the following, you need to have numbers 1-3 OR 1,3, 4 & 5.

  1. Sustained platelet count >450,000

  2. Presence of an acquired pathogenic mutation (eg JAK2, CALR, or MPL)

  3. No other myeloid malignancy, especially PV, PMF, CML, or MDS

  4. No reactive cause for thrombocytosis and normal iron stores

  5. Marrow studies showing increase megakaryocytes displaying a sprectrum of morphology with prominent large hyperlobulated forms.


What is the treatment of ET like?


This score looks at the patient's age (more or less than 60), specific mutations, and history of clot. Patients who are low risk can be observed with low-dose aspirin, but higher risk patients generally need cytoreduction or targeted therapies.


References:

2. MKSAP 17: Chapter 01: Hematopoietic Stem Cells and Their Disorders.

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