3._Bone_marrow__2024

Agenda

  • Opening activity (1:25 PM)

  • Hematology: Bone Marrow (2:30 PM)

  • Week 3 Cases & Closing Activity (2:55 PM)

  • Exit Question (3:05 PM)

Opening Activity

  • Duration: 10 minutes (Starting at 1:25 PM)

Laboratory Evaluation of Bone Marrow

  • Course: VETC 306 Clinical Pathology

  • Instructor: Dr. Sabrina Timperman

Bone Marrow Overview

  • Definition: Tissue enclosed by cortical and cancellous bone.

    • Composed mainly of hematopoietic cells, adipose tissue, and supportive tissue.

  • Red Bone Marrow:

    • Site of hematopoiesis. Initially, all bone marrow is red, transitioning to yellow with aging.

    • Adult sites include: proximal humerus, femur, sternum, ribs, vertebral bodies.

  • Yellow Bone Marrow:

    • Primarily fatty tissue with no hematopoietic function but can revert to red in certain conditions.

Hematopoietic Cells

  • Definition: Precursors to hemic cells found in blood or tissue.

    • Consists of cells in the mitotic (proliferation) pool and post-mitotic (maturation) pools.

  • Lineages:

    • Erythrocyte lineage.

    • Leukocyte lineage.

    • Megakaryocyte lineage.

Reasons to Examine Bone Marrow

  • Diagnosing hematologic abnormalities, including:

    • Nonregenerative anemia.

    • Neutropenia.

    • Thrombocytopenia.

    • Persistent thrombocytosis or lymphocytosis.

    • Abnormal blood cell morphology or unexplained immature cells presence.

    • Determine regenerative status of anemia in horses.

    • Stage neoplastic conditions like lymphoma and mast cell tumors.

Aspirate vs. Biopsy

  • Aspirate:

    • More frequently performed; easier and faster.

    • Stained and examined by pathologist; less expensive.

  • Core Biopsy:

    • Uses bone biopsy needle to obtain a solid core.

    • More accurate evaluation of cellularity and metastatic neoplasia but harder to assess cell morphology.

Contraindications

  • Few contraindications exist:

    • Patients with hemostatic diathesis.

    • Post-aspiration hemorrhage is rare and can be controlled.

  • Risks include:

    • Hemothorax or cardiac tamponade in horses with clotting disorders.

    • Potential post-aspiration infection; requires sterile technique.

Common Bone Marrow Aspiration Sites

  • Dogs:

    • Proximal humerus.

    • Trochanteric fossa of proximal femur.

    • Iliac crest.

  • Cats:

    • Proximal femur and proximal humerus.

    • Accessibility makes these sites preferable.

  • Horses, Cattle, and Camelids:

    • Common sites: ilium, ribs, sternum.

Bone Marrow Aspiration Technique

  • Requires general anesthesia or sedation; local anesthesia is standard.

  • Surgical preparation involves making a small skin incision with a scalpel blade.

  • Bone marrow needle is rotated into the bone until seated.

  • Remove stylet, attach syringe, apply negative pressure until marrow is visible in the barrel.

Slide Preparation for Analysis

  • Smears must be prepared quickly, in seconds if no anticoagulant is used.

  • Slides should be thinly distributed; smear preparation involves holding slides vertically to absorb blood and particles.

  • Stained with Romanowsky stain; air-dried before analysis.

Bone Marrow Core Biopsy

  • Utilizes a Jamshidi needle for core biopsy from proximal femur, proximal humerus, or ilium.

Erythroid Series

  • Overview:

    • Differentiation from myeloid stem cells to BFU-E and then CFU-E cells.

    • Erythropoiesis Process:

      • Rubriblast->Prorubricyte->Rubricyte->Metarubricyte->Reticulocyte->Mature erythrocyte.

    • Important stages of maturation include decreasing cell size, nucleus changes, and cytoplasm color changes.

    • Normal stem cell to RBC release time: 3-5 days.

Regulation of Erythropoiesis

  • Erythropoietin (EPO): Secreted mostly from kidneys, especially in response to hypoxia.

  • Other hormones affecting erythropoiesis: androgens, glucocorticoids, insulin, growth hormone promote; estrogen inhibits.

Granulocyte Series

  • Characterized by granules in the cytoplasm:

    • Types: Neutrophils, Eosinophils, Basophils.

  • Maturation sequence from immature to mature includes:

    • Myeloblast->Promyelocyte->Myelocyte->Metamyelocyte->Band granulocyte->Segmented granulocyte.

Monocyte Series

  • Few in concentration; hard to distinguish from myeloid lineage in normal bone marrow.

  • Maturation includes Monoblast and Promonocyte stages transitioning to mature Monocyte.

Megakaryocyte Series

  • Large, multinucleated cells becoming platelets.

  • Maturation includes Megakaryoblast and Promegakaryocyte stages leading to mature Megakaryocyte.

Other Cells in Bone Marrow

  • Includes Lymphocytes, Plasma cells, Macrophages, Osteoblasts, Osteoclasts, and Mast Cells.

  • Lymphoblast presence is indicative of lymphoproliferative disorders.

Approach to Bone Marrow Evaluation

  • Use low power objective (100x) to scan for overall cellularity and assess adequacy of sample.

  • Normal marrow is heterogeneous; increased fat vs. nucleated cells indicates abnormal populations.

  • Examine the ratio of granulocytic to erythroid cells (Myeloid to Erythroid Ratio - M:E) by counting 500 cells.

Stem Cell Disorders of Marrow

  • Reversible Stem Cell Injuries:

    • Usually transient; caused by viral agents, chemotherapeutics, or chemicals affecting rapidly dividing cells.

    • Results in neutropenia, thrombocytopenia, and nonregenerative anemia; recovery expected after a couple of weeks.

  • Irreversible Stem Cell Injury:

    • Caused by FeLV in cats or unknown factors in other animals; can result in aplasia, dysplastic production, or neoplastic production.

    • Myelodysplasia represents abnormal development leading to cytopenias, more common in cats.

Neoplastic Disorders in Bone Marrow

  • Myeloproliferative Neoplasia: Neoplastic proliferation from cells in the marrow including various leukemias.

  • Lymphoproliferative Neoplasia: Derived from lymphocytes, with types such as acute lymphoblastic leukemia and plasma cell myeloma.

  • Broad classification of leukemias into acute (rapid progression, replacement by blast cells) and chronic (milder progression with some retained function).

  • Management and prognosis vary significantly between acute and chronic presentations.