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Leukemia

BASICS

DEFINITION/OVERVIEW

Leukemia is a neoplasia of the white blood cells, which starts in the bone marrow.

ETIOLOGY/PATHOPHYSIOLOGY

No confirmed etiology has been proved for any of the leukemia cases described in chelonians, including viral etiology.

Leukemias are classified as myeloid or lymphoid, depending upon the neoplastic blood cell.

It is generally accepted, based on previously reported cytochemical staining characteristics, that reptilian granulocytes, monocytes, and azurophils are from the myeloid cell lineage, whereas reptilian lymphocytes are from the lymphoid cell lineage.

Leukemias are commonly graded as acute or chronic depending on the number of blast cells in peripheral circulation.

Blast cells predominate in acute leukemia, whereas mature forms predominate in chronic onset leukemia, with less than 30% of the peripheral leukocytes being blast cells.

Acute leukemias are rapidly fatal in untreated patients.

SIGNALMENT/HISTORY

Leukemia in chelonians has been reported in both adult and immature turtles.

CLINICAL PRESENTATION

Anorexia and lethargy are frequently reported.

Weight loss is common in chronic leukemia.

RISK FACTORS

Husbandry

N/A

Others

N/A

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

Multiple myeloma or plasma cell myeloma.

Monoclonal gammopathy

DIAGNOSTICS

Hemogram: a marked leukocytosis characterized by lymphocytosis/monocytosis (depending upon the type of leukemia) can be observed.

Cytological evaluation of blood smears and/or bone marrow biopsy (because of the extensive bony trabecular network, conventional bone marrow aspirates in chelonians have low cell yield; bone marrow

may be collected from the gular projection of the plastron or the bridge of the plastron and carapace) (Silverstone et al, 2007).

Necropsy and subsequent histopathology

Cytochemical and immunocytochemical stains to confirm cell lineage.

Cytochemical staining can include α-naphthyl butyrate esterase, chloroacetate esterase, Sudan black B, and alkaline phosphatase to distinguish myeloid or lymphoid origin; it is important to study comparison samples from both clinically healthy and affected animals of the same species because of the paucity of cytochemical characterization of blood cells for most reptiles. CD3 antibody identifies T-cell lymphocytes and Pax-5 and BLA36 antibodies identify B-cell lymphocytes (Silverstone et al, 2007; Bezjian et al, 2013). L1-calprotectin antibody has been used to identify myeloid cells in lizards.

Transmission electron microscopy can be attempted to determine histogenesis and to identify viral particles.

PATHOLOGICAL FINDINGS

Cytological evaluation of blood smears and/or bone marrow aspirates can reveal abnormal cell morphology of the neoplastic cells, abnormal nuclear to cytoplasm ratio, and anisokaryosis; mitotic figures are frequently detected.

Histopathologic examination of tissue samples can reveal infiltration of neoplastic cells in several organs and occasional mitotic figures.

TREATMENT

APPROPRIATE HEALTH CARE

N/A

NUTRITIONAL SUPPORT

An esophagostomy tube should be considered in anorexic animals or for long-term administration of medications.

CLIENT EDUCATION/HUSBANDRY RECOMMENDATIONS

An early diagnosis can maximize the success of therapy.

MEDICATIONS

DRUG(S) OF CHOICE

Silverstone et al (2007) treated a diamondback terrapin (Malaclemys terrapin) suffering from lymphoblastic leukemia with prednisone 0.6 mg/kg PO q48h, cytosine arabinoside 6 mg/kg SQ q7d for two treatments, and chlorambucil 1 mg/kg PO q7d for two treatments; at 24 days post-treatment, the WBC count and the turtle’s activity had improved, but it died 46 days after the beginning of treatment.

Cytosine arabinoside is the most frequently used treatment for small mammals with chronic monocytic leukemia, whereas prednisone therapy is widely used and accepted for small mammals with lymphoid leukemia and lymphoma; it is not effective for myeloid leukemias.

PRECAUTIONS/INTERACTIONS

Suspected cytosine arabinoside toxicity characterized by renal failure has been reported in a rhinoceros viper.

FOLLOW-UP

PATIENT MONITORING

Complete blood count must be done for monitoring the overall WBC count and different leukocyte counts to gauge response to the drugs.

EXPECTED COURSE AND PROGNOSIS

The prognosis of the disease, especially in acute leukemia, is poor.

MISCELLANEOUS

COMMENTS

N/A

ZOONOTIC POTENTIAL

N/A

SYNONYMS

N/A

ABBREVIATIONS

PO = per os

SC = subcutaneous

WBC = white blood cells