L-17 Myeloproliferative Disorders: White Cell Proliferation

• Myeloproliferative and related disorders involve pathological proliferations of white cells.

Pathological Proliferation of White Cells

• Myeloid proliferation can be physiological, such as a response to antigens, or pathological, such as leukemia.
• Myeloid cells include neutrophils, eosinophils, basophils, and monocytes.
• Peripheral blood sample collection and smear are important diagnostic tools.
• Normal white blood cell (WBC) count is 4-11k/uL.
• Rate of release of cells, margination pool, and blood/tissue distribution affect WBC counts.

Leukocytosis

• Leukocytosis is a reaction to inflammation and exhibits an increase in WBCs above the upper limit of normal.
• Leukocytosis with neutrophilia is the response to infection and/or stress.
• Left shift and toxic granulation are features of neutrophilic response to infection or stress.
• Leukemoid reaction involves a leukocytic response > 50x10^9/L or higher with a left shift.
• Basophilia is associated with myeloproliferative disorders.
• Monocytosis is associated with chronic bacterial infections.
• Lymphocytosis is associated with viral infections and Mycobacterium infections.

Leukopenia

• Leukopenia involves a WBC count < 4k/uL
• It is associated with advanced HIV infection, therapy with glucocorticoids or cytotoxic drugs, autoimmune disorders and malnutrition.
• Neutropenia involves a reduction in the number of granulocytes in the peripheral blood.
• Neutropenia is defined as < 1,500/uL.
• Neutropenia happens due to reduced or ineffective production of neutrophils.
• Accelerated removal of neutrophils from circulation can also cause neutropenia.
• Neutropenia can be caused by suppression of myeloid stem cells from drug exposure.
• Drugs include: Clozapine, Methimazole/Propylthiouracil, Penicillin G, Procainamide, Sulfasalazine, and Ticlopidine.
• Ineffective granulopoiesis can result in neutropenia.
• Accelerated removal or destruction of neutrophils can also cause neutropenia.
• Neutropenia results from immunologically mediated injury, splenic sequestration, and increased peripheral demand.

Bone Marrow Evaluation

• Bone marrow changes are associated with neutropenia.
• Peripheral destruction causes marrow to be hypercellular.
• Suppression/destruction of granulocytic precursors causes marrow to be hypocellular.
• Bone marrow evaluation includes bone marrow aspiration and examination.
• Bone marrow examination includes M:E ratio, which is normally 3:1.
• Myeloid to Erythroid ratio is collected from bone marrow smear.
• A 5:1 ratio suggests a myeloproliferative process.

Myelodysplastic Syndromes (MDS)

• MDS includes refractory anemia, refractory anemia with ringed sideroblasts, refractory anemia with excess blasts, and refractory anemia with excess blasts in transformation.
• MDS typically affects older adults.
• The mean age of onset is 70 years.
• MDS is often discovered incidentally on routine blood testing but can have symptomatic presentations.
• Symptomatic presentation of MDS includes weakness, infections, hemorrhages and pancytopenia.

Characteristics of MDS

• Dysplasia in one or more myeloid lineages.
• Ineffective hematopoiesis, cytopenia and genetic abnormalities are key components.
• Increased risk of developing AML is a concern.
• Myeloblasts in periphery or bone marrow (<20%).
• Potential bone marrow replacement of pluripotent stem cells occurs.
• MDS can be idiopathic (primary) or therapy related (t-MDS).
• Pathogenesis involves gene mutations and dysregulation of the epigenome.
• Dysregulation affects DNA methylation, histone modifications, chromatin looping, RNA splicing factors, and transcription factors.

Morphology of MDS

• Morphology includes normo- or hypercellular BM.
• You might also see basophilia, Pseudo Pelger-Huet, megalablastoid maturation, ringed sideroblasts.
• Diagnostics findings of myelodysplasia may show hypercellular bone marrow, basophilia, and nucleated red cell progenitors with multilobated or multiple nuclei.
• Ringed sideroblasts are erythroid progenitors with iron-laden mitochondria, seen as blue perinuclear granules with Prussian blue stain.
• Pseudo-Pelger-Hüet cells, neutrophils with only two nuclear lobes instead of the normal three to four may be present.
• Megakaryocytes with multiple nuclei instead of the normal single multilobated nucleus can be indicators for megalablastoid maturation.
• MDS can progress to AML.
• Therapy-related MDS (t-MDS) has a rapid progression to AML.

Myeloid Neoplasms

• Myeloid neoplasms include:
  • Acute Myeloid Leukemia
  • Myelodysplastic Syndrome
  • Myeloproliferative Neoplasms
  • Chronic Myeloid Leukemia
  • Polycythemia Vera
  • Essential Thrombocytosis
  • Primary Myelofibrosis

Acute Myeloid Leukemia (AML)

• The WHO classification of AML includes subtypes with genetic aberrations, MDS-like features, therapy-related AML ,and AML not otherwise specified.
• AML is diagnosed by > 20% myeloid blasts in the bone marrow.
• Auer rods are abnormal azurophilic granules associated with (M3 type) AML.
• Acute promyelocytic leukemia with the t(15;17) (FAB M3 subtype) is identified via marrow aspirate.
• Neoplastic promyelocytes exhibit coarse, numerous azurophilic granules.

Acute Myelogenous Leukemia (AML) Information

• Myeloblasts have 2-4 nucleoli and a volume larger than lymphoblasts.
• Myeloid markers for AML are CD 34, 38, 44, 59.
• Similar symptoms to ALL, related with bone marrow (BM) failure.
• These include anemia, neutropenia, thrombocytopenia, and bleeding diathesis.
• Bleeding diathesis is exacerbated by procoagulant and fibrinolytic factors from leukemic cells
• Other symptoms include cutaneous petechiae and ecchymoses, and serosal hemorrhage.
• Clinical features include skin/gingival infiltration, lymphadenopathy, organomegaly, infections, and CNS involvement.
• Approximately 60% achieve complete remission with chemotherapy, and 15-30% are disease-free after 5 years.
• (8;21)t indicates good prognosis but Philadelphia chromosome (9;22)t indicates unfavorable prognosis
• Favorable abnormalities include translocation between chromosomes 8 and 21 (M2 patients) and translocation/inversion of chromosome 16.
• Also there is translocation between chromosomes 15 and 17, typical in M3 patients.
• A common pathogenic feature: mutated and constitutively activated tyrosine kinases.
• Acquired aberrations in signaling pathways lead to growth factor independence.
• Aberrations associated with Chronic myelogenous leukemia are the BCR-ABL fusion gene at 100%.
• Aberrations associated Polycythemia vera are the JAK2 point mutations at >95%.
• Aberrations associated with Essential thrombocythemia include JAK2 point mutations at 50% to 60% and MPL point mutations at 5% to 10%.
• Aberrations associated with primary myelofibrosis is JAK2 point mutations at 50% to 60%.

Chronic Myeloproliferative Disorders

• The general pathogenic feature is constitutively activated tyrosine kinases leading to the the growth factor-independent proliferation and survival of marrow progenitors.
• Conditions include:
  • Chronic Myelogenous Leukemia (CML)
  • Polycythemia Vera (PV)
  • Essential Thrombocytosis
  • Primary Myelofibrosis

Chronic Myelogenous Leukemia (CML)

• CML is a disease of adults, commonly occurring between ages 25-60.
• Translocation occurs with the BCR gene on chromosome 9, and the ABL gene on chromosome 22, which form the Philadelphia chromosome.
• The BCR-ABL fusion gene results in abnormal automatic accelerated cell division.
• It features a 210 kDa protein and constitutively active tyrosine kinase.
• Autophosphorylation, autonomous and myeloproliferation are also features.

CML Morphology and Clinical Features

• Morphology includes hypercellular BM, increased reticulin fibers, and peripheral blood leukocytosis.
• Peripheral blood exhibits neutrophils, bands, eosinophils, basophils, metamyelocytes, and myelocytes.
• Clinical features include insidious onset, mild-to-moderate anemia, anemia with weight loss, hypermetabolic state, and progression to acute leukemia (blast crisis).

Polycythemia Vera (PV)

• PV features a chronic myeloproliferative neoplasm and increase in red blood cells.
• It involves mutations, specifically in JAK V617F and JAK 2 (Panmyelosis).
• There are two phases, the polycythemic phase and spent phase.
• The polycythemic phase features elevated Hgb, increased hematocrit, and increased RBC mass.
• The spent phase features Ineffective hematopoiesis, bone marrow fibrosis, extramedullary hematopoiesis, and hypersplenism.

Polycythemia Vera (PV) Microscopy

• Microscopy reveals peripheral blood proliferation.
  • This includes RBCs(Normochromic normocytic), Granulocytes, and a Megakaryocytic Lineage.
• Bone marrow is usually Hypercellular, and often Panmyelosis.
• Increased erythroid precursors and megakaryocytes are the most prominent.

Essential Thrombocytosis (ET)

• ET involves activating point mutations in JAK2 (50% of cases) and MPL (5-10% of cases).
• Receptor tyrosine kinase is activated by thrombopoietin.
• Mutations in calreticulin increase JAK-STAT signaling.
• Thrombopoietin is a glycoprotein hormone regulating the production of platelets which is produced by the liver and kidney.
• Clinical manifestations include elevated platelet counts, and absence of polycythemia / marrow fibrosis.
• Absence of Tyrosine kinase mutations is important when excluding other causes of thrombocytosis.
• Also, exclude inflammatory disorders and iron deficiency.
• Platelets progenitors are, thus, thrombopoietin-independent, leading to hyperproliferation.

Essential Thrombocytosis Bone Marrow & Smears

• Bone Marrow exhibits mildly increased Megakaryocytes.
• Also, delicate reticulin fibrils are often seen.
• Note that fibrosis of primary myelofibrosis is absent.
• Peripheral smears exhibit abnormally large platelets and mild leukocytosis.
• May have extramedullary Hematopoiesis with Mild organomegaly.

Essential Thrombocytosis (ET) Demographics & Clinical Manifestations

• The incidence is 1 to 3 per 100,000 / year.
• It features an indolent course and long asymptomatic periods with age > 60.
• Median survival times are 12 to 15 years.
• Major Clinical Manifestations
• Thrombosis and Hemorrhage
  • Deep Venous Thrombosis
  • Portal and Hepatic Vein Thrombosis
  • Myocardial Infarction and Erythromelalgia.
  • Rare condition that causes episodes of burning pain and redness in the feet, and sometimes the hands, arms, legs, ears and face.