Introduction

The bone marrow is a highly cellular tissue that is found restricted to the cavities of the bone tissue. The active marrow (red cord) is involved in the formation and release of several lineages of blood cells, storage and recycling of iron, phagocytosis of cellular debris and production of antibodies. Many pathological disorders of the bone marrow are described in Veterinary Medicine, and routine laboratory tests do not conclude the diagnosis, thus the cytological evaluation of bone marrow has become necessary and essential to assist in the elucidation of certain diseases that affect dogs and cats (Thrall 2007). The cytology of the bone marrow, or myelogram, is considered a little invasive procedure, faster and easier when compared to biopsy, and do not cause damage to the animal. The most addressed sites for the puncture in dogs and cats are: proximal end of the femur (trochanteric fossa), iliac crest, proximal humerus, costal arch (costochondral junction) and sternum. The material is obtained by aspiration with specific needle (Jamshidi 16G), requiring local infiltrating anesthesia, analgesic and sedation, and if the sensitivity of the patient persists, general anesthetic procedure is used to perform the test (Grindem et al. 2002). After obtaining the material the smears are prepared and stained by the Rosenfeld method and observed in optical microscope (lowest magnification) to evaluate the cellularity, maturative staggering of blood lineages, presence of cellular neoplastic elements or infectious agents, in which a good quality material is essential to the definitive diagnosis (Harvey 2001, Thrall 2007). The normal bone marrow cellularity is variable and depends mainly on the age of the individual. Usually about 50% of the red marrow consists of nucleated cells and 50% yellow marrow, corresponding to fat. The nucleated cellular elements found correspond to erythroid, myeloid, monocytic, lymphocytic, megakaryocytic and the medullar stroma lineages (Grindem et al. 2002). The main myeloproliferative disorders are related to the increased cellularity of the myeloid or erythroid lineages that may be related to blood loss response and cellular destruction. The main lymphoproliferative disorders are related to neoplastic processes (Thrall 2007). However, hypocellularity can be observed in cases of myelofibrosis, presence of infectious agents (Ehrlichia sp. in dogs and feline leukemia virus in cats), intoxication mediated by chemical substances and drugs, radiation and immune-mediated diseases (Schalm 2002, Thrall 2007). The myelogram is indicated in cases of unexplained changes in the blood cell count (thrombocytopenia, nonregenerative anemia, leukopenia, polycythemia, pancytopenia, morphological changes of erythrocytes and abnormal elements in the bloodstream), hypercalcemia, fever of unknown origin, suspected myelophage, hyperproteinemia (polyclonal or monoclonal gammopathy), therapeutic monitoring (chemotherapy), among others (Harvey 2001). The main contraindication occurs in patients with haemostatic disorders, resulting in bleeding after collection. Thus, the fulfillment of laboratory tests is essential (complete blood cell count with platelet count and coagulogram) in patients with bleeding diathesis before the puncture of the bone marrow (Grindem et al. 2002, Thrall 2007).

Materials and Methods

In this study 26 samples were analyzed (23 dogs and 3 cats) obtained from bone marrow cytology aspirate, collected in the Anhembi Morumbi Veterinary Hospital in the period from 2005 to 2007. Before performing the procedure, the animals were submitted to mild sedation and analgesia with 4 mg.kg^-1 of pethidine hydrochloride (dolosal ®) and local infiltrative anesthesia with up to 1 ml of lidocaine hydrochloride (lidocaine ® 2%). In the site of the puncture trichotomy and anti-sepsis were performed for the introduction of the needle Jamshidi (16G) and aspiration of the material. The smears were prepared using the technique of "squash" and stained by the Rosenfeld method. All samples were analyzed in light microscopy (objective of immersion in 100X) with 500 cells count per slide.

Results

The main changes that justified an indication for the myelogram were: nonregenerative anemia, thrombocytopenia, leukopenia, pancytopenia, erythrocytosis, the presence of blasts or other neoplastic elements in peripheral blood and hyperproteinemia. According to the results achieved in the myelogram (n = 26) it was possible to indicate the diagnosis of leukemia (n = 7), classified as acute and chronic lymphocytic, acute myelocytic and monocytic, associating cytochemistry; polycythemia vera (n = 1); canine ehrlichiosis (n = 4); mieloftise (n = 3), necrosis of bone marrow (n = 1) nonregenerative anemia due to renal failure (n = 2); immune-mediated diseases (n = 8) consistent with immune-mediated hemolytic anemia, systemic lupus erythematosus and immune-mediated thrombocytopenia.

Discussion and Conclusions

By the findings of the myelogram the definitive diagnosis was conclusive in 57.7% of the cases, not making the use of other laboratory tests necessary. In cases of leukemia more than 30% of blastic cells were observed, and the lymphoblastic leukemia was predominant; in canine ehrlichiosis the presence of Ehrlichia sp morulae in mononuclear; in mieloftise with visualization of neoplastic elements and spinal cord necrosis with hypocellularity and cellular degeneration. However, in some cases, the cytological test did not confirm the suspected diagnosis and the realization of other laboratory methods was necessary such as: dosage of erythropoietin for confirmation of the polycythemia vera; dosage of ANA (anti-nuclear antibodies) for the confirmation of systemic lupus erythematosus and biochemical dosage of nitrogen compounds in renal failure. In cases of hemolytic anemia and immune-mediated thrombocytopenia, therapeutic diagnosis was realized with the institution of immunosuppressive protocol. However, it's important to emphasize that the use of different diagnostic methods associated with the myelogram cooperate with the conclusion of the diagnosis, the monitoring and the establishment of an effective therapeutic protocol.

References

1.  Harvey JW. 2001. Bone marrow examination, p. 83-161. In: Harvey JW. Atlas of Veterinary Hematology: Blood and Bone Marrow of Domestic Animals. 1st ed, Ed Saunders, Philadelphia

2.  Grindem CB, Juopperi TA, Neel JA. 2002. Cytology of bone marrow. Vet Clin Small Animals, 32: 1313-1374;

3.  Schalm OW. 2002. Bone marrow cytology as an aid to diagnosis. Symposium on Clinical Hematology, p.383404;

4.  Thrall MA. 2007. Avaliação Laboratorial da Medula "ssea, p. 141-169. In: Thrall MA. Hematologia e Bioquímica Clínica Veterinária. 1st ed., Ed Roca, USA.