"Bone Marrow Evaluation" TUMOR TIDBITS, A BIWEEKLY VETERINARY ONCOLOGY E-LETTER Volume 2; Number 13; August 15, 2001. Editor: Kevin A. Hahn, DVM, PhD, Dipl - ACVIM (Oncology) & Overall Nice Guy! ANNOUNCEMENTS FROM ONCOLOGY 1 - We now have an office open in Tomball on Mondays and San Antonio on Thursdays in addition to our regular office hours in Houston; when in doubt - we can check it out!). 2 - We are actively recruiting pets with or without cancer to enter a plasmid therapy study. This plasmid contains a product that, in our preliminary data, improves red blood cell counts, total protein, body muscle mass, and wellness. There is no cost for the trial and it involves evaluation every 2 weeks for 2 months. Call our Houston office for additional information and appointments. THIS WEEK'S TUMOR TIDBIT: BONE MARROW EVALUATION The evaluation of bone marrow is an important tool in the diagnosis of hematologic disorders and the staging of certain neoplasms. Proper sample collection and slide preparation may provide the basic information needed to assist in patient diagnosis or prognosis. INDICATIONS In most cases, indications for doing a bone marrow aspirate are determined by evaluation of a CBC on the peripheral blood. In fact, it is often impossible to interpret findings in the marrow without a recent CBC. The following is a list of indications for evaluation of a bone marrow aspirate. ANEMIA Bone marrow aspirates should be performed whenever there is a nonregenerative or poorly regenerative anemia. It is not necessary to evaluate the bone marrow in cases of regenerative anemias since the marrow is showing evidence of adequate red cell production. LEUKOPENIA Reduced leukocyte numbers may result from lymphopenia or neutropenia. Lymphopenia is usually not an indication of decreased marrow production and does not typically require marrow evaluation. Neutropenia on the other hand may result from decreased production from the marrow or increased use or destruction in the periphery. A persistent neutropenia is a good indication for bone marrow evaluation. THROMBOCYTOPENIA A bone marrow aspirate is important in differentiating a production problem verses a peripheral destruction or utilization of platelets in patients with a peripheral thrombocytopenia. UNEXPLAINED ELEVATIONS IN CELL NUMBERS Persistent polycythemia, leukocytosis, or thrombocytosis without evidence of a clinical disease that could account for these findings is an indication for bone marrow evaluation. ABNORMAL CIRCULATING CELLS The presence of abnormal cells in the peripheral blood may be an indication of neoplasia in the bone marrow, and is an important indication for marrow evaluation. These may be in the form of hematopoietic blast cells such as lymphoblasts or myeloblasts or dysplastic cells. Dysplasia is defined as an abnormal maturation of cells and is usually associated with a preleukemia or leukemia. Some examples of dysplastic changes are nucleated red blood cells without evidence of polychromasia, abnormally large metarubricytes, hypersegmented neutrophils, giant metamyelocytes, megaplatelets, and dwarf megakaryocytes. Other clinical conditions may cause dysplastic changes in circulating cells besides leukemia or preleukemia. Lead poisoning may cause circulating NRBC's without polychromasia, and steroid administration is the most common cause of hypersegmentation of neutrophils. Additionally, the presence of non-hematopoietic cells in the peripheral circulation may be an indication for bone marrow evaluation. The presence of cells not normally found in circulation may suggest metastasis of a neoplasm to the marrow. The classic example, and probably most common, is the presence of mast cells in the blood of an animal with a mast cell tumor. CLINICAL STAGING OF MALIGNANCY The absence of circulating neoplastic cells does not ensure the bone marrow is free of metastatic disease. This is particularly true of animals with lymphoma. Therefore, a marrow evaluation is necessary for clinical staging and prognosticating. UNEXPLAINED HYPERCALCEMIA In the dog, hypercalcemia is most often the result of a paraneoplastic syndrome associated with a lymphoid neoplasia or an anal sac apocrine gland adenocarcinoma. In cases of hypercalcemia without lymph node or anal sac involvement, a bone marrow evaluation is of paramount importance. The majority of these animals have a lymphoid leukemia where only the bone marrow is involved. Circulating tumor cells may not be found in the peripheral blood. MONOCLONAL GAMMOPATHY Monoclonal gammopathies are due to an increased production of a single immunoglobulin. This usually results from uncontrolled growth of a clonal population of B-lymphocytes. In small animals, monoclonal gammopathies are most often associated with lymphoproliferative disorders. Immunoglobulin-producing tumors include multiple myeloma, chronic lymphocytic leukemia, primary macroglobulinemia (Waldenstrom's Syndrome), and lymphoma. A bone marrow aspirate is often needed to identify the neoplastic lymphocyte population. MATERIALS NEEDED Bone marrow aspirates are performed using a sterile, 15 to 18 gauge Illinois sternal/iliac bone marrow aspiration needle (Pharmaseal Division of Baxter Healthcare Corp., Valencia, CA). For core biopsies, a Jamshidi biopsy needle (11 gauge, 4 inches) should be used. Prior to aspiration of a sample, approximately 0.2 cc of anticoagulant (5% EDTA or Heparin sulfate) will be aspirated into a sterile 12 cc syringe. A 2% Lidocaine solution will be needed for local anesthetic to the periosteum in patients not undergoing general anesthetic. A petri dish or other clear glass surface will be used to apply the marrow to in order to allow the peripheral blood contamination to be tilted away from the marrow particles once aspirated. The marrow particles will adhere to the surface of the petri dish where they can be removed by capillary action with a hematocrit capillary tube and transferred to a microscope slides for smearing. Diff Quik or other comparable stain can be used to fix and stain the air-dried smears. SAMPLE COLLECTION The hair is clipped and the bone marrow aspiration site is prepared with a surgical scrub. Preferred sites and patient positioning include: dorsocranial or lateral aspects of iliac crest (patient is sternal); greater trochanter of the femur (patient is in lateral recumbency); greater tubercle of the proximal aspect of the head of the humerus (patient is in lateral recumbency) Using a 25 gauge needle, approximately 2 to 3 mls of the local anesthetic agent, lidocaine, are injected in and around the site where the bone marrow needle is to be introduced. Care is taken to deposit lidocaine in and around all of the tissues that extend from the skin to the bone. The biopsy area is scrubbed a final time after the lidocaine is injected. A surgical drape may be applied for sterility. The bone marrow site is identified, the skin is stretched between the thumb and index finger, and a small stab incision is made with a number 11 surgical blade in the area blocked with lidocaine. The bone marrow needle with the stylette in place is advanced through the stab incision in the skin, subcutaneous tissue, and muscle down to the bone. It is crucial to keep the stylette in place because it has a tendency to back out during the procedure. A 1 to 1.5 inch long, 16 gauge Illinois or Rosenthal bone marrow needle is preferred for dogs, and a 1-inch long, 18 gauge Illinois or Rosenthal needle is preferred for the cat. After a sample is obtained for cytologic evaluation, if a biopsy is required, a Jamshidi needle is utilized. With the stylette is place; the bone marrow needle is advanced into the bone using a corkscrew motion. The instrument should not be allowed to wobble and the instrument should be fixed firmly into bone like a nail that has been securely hammered into wood. When the needle is firmly fixed in the bone, the stylette is removed and the syringe is affixed. Many clinical pathologists suggest rinsing the syringe and bone marrow needle with EDTA or heparin before the procedure to reduce clotting of the bone marrow sample. The bone marrow sample is then aspirated briskly into the 12 ml syringe; usually 1 ml is adequate. The aspiration may be accompanied with a few seconds of pain, but this cannot be prevented. If a sample is not obtained, the stylette is replaced in the bone marrow needle and the instrument is then advanced further into the bone for a second attempt at aspirating marrow contents. Once marrow has been obtained, smears are prepared. The particle is blown onto one edge of a clean microscope slide and a second slide is laid parallel on top of the first. The weight of the slide will cause the material to diffuse out leaving the particle in the center. The slides are gently slid apart making an even smear with marrow particles in the center of the slide. The slides are then stained with Diff Quik or a comparable stain. MORE QUESTIONS ABOUT BONE MARROW PROCEDURES? Don't hesitate to call or email us at Gulf Coast Veterinary Oncology! I can forward additional info by email if needed. IN 2 WEEKS: INTERPRETATION OF BONE MARROW SLIDES! ALL THE BEST, Kevin Hahn Kevin A. Hahn, DVM, PhD Diplomate ACVIM (Oncology) & Overall Nice Guy Gulf Coast Veterinary Specialists 1111 West Loop South, Suite 150 Houston, TX 77027 P: 713.693.1166 F: 713.693.1167 www.gcvs.com drhahn@g...