Introduction

A 3-year-old 0.554-kg (1.22-lb) female bearded dragon (Pogona vitticeps; bearded dragon 1) was examined by the North Carolina State University College of Veterinary Medicine's Exotic Animal Medicine Service because of a persistent left ocular discharge. Two weeks prior to this examination, the patient had been evaluated by the referring veterinarian because of mucoid green ocular discharge, conjunctivitis, and blepharospasm. A CBC at that time revealed moderate leukocytosis (20.0 × 10³ WBCs/μL; reference range,¹ 1.45 × 10³ to 19.0 × 10³ WBCs/μL) characterized by mild heterophilia (7.8 × 10³ heterophils/μL; reference range,¹ 0.24 × 10³ to 7.77 × 10³ heterophils/μL), marked monocytosis (8.8 × 10³ monocytes/μL; reference range,¹ 0.03 × 10³ to 1.39 × 10³ monocytes/μL), and a normal lymphocyte count (3.2 × 10³ lymphocytes/μL; reference range,¹ 0.29 × 10³ to 11.3 × 10³ lymphocytes/μL). The patient was treated with enrofloxacin (10 mg/kg [4.5 mg/lb], PO, q 24 h), doxycycline (5 mg/kg [2.3 mg/lb], PO, q 24 h), meloxicam (0.2 mg/kg [0.09 mg/lb], PO, q 24 h), and an ophthalmic ointment containing polymyxin B sulfate, neomycin sulfate, and bacitracin zinc (applied to the left eye, q 12 h), and ocular flushing was performed by the referring veterinarian. The patient's condition improved; however, serous left ocular discharge persisted, and the patient was referred for further examination.

At the time of initial examination by the Exotic Animal Medicine Service 2 weeks later, the patient had mild chemosis, blepharospasm, and enophthalmos of the left eye. An approximately 1 × 1.5-cm coelomic mass was palpated. A CBC was performed with a manual differential cell count and revealed leukocytosis (24.0 × 10³ WBCs/μL) characterized by lymphocytosis (19.9 × 10³ lymphocytes/μL) and normal heterophil (2.9 × 10³ heterophils/μL) and monocyte (0.24 × 10³ monocytes/μL) counts. A veterinary clinical pathologist who reviewed the blood smear identified a high number of intermediate-sized lymphocytes that were lightly basophilic, with rare cells containing 1 to 2 medium-sized, round, clear cytoplasmic vacuoles. These lymphocytes were considered suggestive of lymphoid neoplasia, although an inflammatory response could not be ruled out. The patient was discharged, and the owner was instructed to administer prednisolone acetate 1% ophthalmic solution (1 drop in the left eye, q 8 h), continue all other current medications, and return for a recheck CBC in 1 week.

During a recheck examination 10 days later, the ocular signs had resolved. However, the patient had developed a poor appetite and become lethargic. A CBC and serum biochemical analyses revealed progressive leukocytosis (109.6 × 10³ WBCs/μL) characterized by marked lymphocytosis (101.9 × 10³ lymphocytes/μL). A review of the blood smear showed a high proportion of abnormal lymphocytes that were monomorphic and intermediate in size. These lymphocytes had round to slightly indented nuclei with less condensed chromatin, inconspicuous nucleoli, and mildly increased amounts of clear to basophilic cytoplasm. Rare large cells with finely stippled chromatin and prominent nucleoli and plasmacytoid cells were also present (Figure 1). The findings were consistent with lymphoid neoplasia.

Coelomic ultrasonography revealed ovarian follicles with irregularly ovoid structures in the mid-left aspect of the coelom that were suspected to be partially collapsed, retained ova. A small volume of coelomic effusion was also noted. Treatment with prednisolone (1 mg/kg [0.45 mg/lb], PO, q 24 h) and ceftiofur crystalline free acid (30 mg/kg [13.6 mg/lb], SC, q 10 d) was initiated, and administration of all other medications was discontinued.

Photomicrographs of blood smears from 5 bearded dragons (Pogona vitticeps) with lymphoid leukemia. Images A through E correspond to bearded dragons 1 through 5, respectively. Images contain neoplastic lymphocytes (asterisks), normal lymphocytes (L), and RBCs (r). Neoplastic lymphocytes are larger than normal lymphocytes and characterized by fine to lightly clumped chromatin and increased amounts of blue cytoplasm. Cytoplasmic fragments, commonly seen with lymphoid neoplasia, are indicated (arrows; D). Wright-Giemsa stain; bar = 10 μm.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Photomicrographs of blood smears from 5 bearded dragons (Pogona vitticeps) with lymphoid leukemia. Images A through E correspond to bearded dragons 1 through 5, respectively. Images contain neoplastic lymphocytes (asterisks), normal lymphocytes (L), and RBCs (r). Neoplastic lymphocytes are larger than normal lymphocytes and characterized by fine to lightly clumped chromatin and increased amounts of blue cytoplasm. Cytoplasmic fragments, commonly seen with lymphoid neoplasia, are indicated (arrows; D). Wright-Giemsa stain; bar = 10 μm.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Photomicrographs of blood smears from 5 bearded dragons (Pogona vitticeps) with lymphoid leukemia. Images A through E correspond to bearded dragons 1 through 5, respectively. Images contain neoplastic lymphocytes (asterisks), normal lymphocytes (L), and RBCs (r). Neoplastic lymphocytes are larger than normal lymphocytes and characterized by fine to lightly clumped chromatin and increased amounts of blue cytoplasm. Cytoplasmic fragments, commonly seen with lymphoid neoplasia, are indicated (arrows; D). Wright-Giemsa stain; bar = 10 μm.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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The patient was returned 5 days later for initiation of chemotherapy and, at that time, appeared brighter with an improved hydration status. The owners reported an increased appetite at home. A CBC revealed improvements in leukocytosis (30.9 × 10³ WBCs/μL) and lymphocytosis (24.7 × 10³ lymphocytes/μL). The patient was given an injection of l-asparaginase (400 U/kg [182 U/lb], SC) and a dose of lomustine (80 mg/m², PO). Body surface area was estimated as (K × W^2/3)/10⁻⁴, where K, the shape constant, was assumed to be 11 and W was body weight in grams. Three weeks later, the patient was returned and again received l-asparaginase and lomustine at the same doses. The patient received a total of 2 doses of l-asparaginase and 8 doses of lomustine at approximately 3-week intervals. Partial remission was achieved, with the lowest lymphocyte count occurring after the fifth dose of lomustine (18.8 × 10³ lymphocytes/μL); at that time, the leukocyte count was 23.5 × 10³ WBCs/μL. The longest interdose interval was 3 months and occurred between the seventh and eighth doses of lomustine as a result of owner unavailability. At a recheck examination after this prolonged interval, the patient was deemed to have progressive disease (leukocyte count, 85.7 × 10³ WBCs/μL; lymphocyte count, 70.3 × 10³ lymphocytes/μL; Figures 2 and 3). During the initial course of treatment, the patient developed several dermal nodules that were suspected to be sterile abscesses due to multiple injections of ceftiofur crystalline free acid. Cytologic examination of an aspirate sample revealed adipocytes, spindle cells, and heterophilic and macrophagic inflammation. The nodules resolved without treatment, and no other complications were noted.

One month after the eighth lomustine dose was given, the patient was returned for a recheck evaluation. A CBC revealed leukocytosis (84.0 × 10³ WBCs/μL) and lymphocytosis (57.9 × 10³ lymphocytes/μL), and the patient was reported to be more lethargic and to have a poor appetite. At this time, the patient was given a single dose of cyclophosphamide (3 mg/kg [1.4 mg/lb], PO), and the owner was instructed to continue all other medications. At a recheck evaluation 2 weeks later, the patient had achieved a second partial remission (leukocyte count, 34.2 × 10³ WBCs/μL; lymphocyte count, 21.9 × 10³ lymphocytes/μL) and was reported to have an improved appetite and increased energy. The patient was given an injection of L-asparaginase (400 U/kg, SC) and a second dose of cyclophosphamide (3 mg/kg, PO). Progressively higher doses of cyclophosphamide were administered every 2 weeks because of ongoing lymphocytosis. The patient was ultimately given 2 doses of cyclophosphamide at 3 mg/kg, 3 doses of cyclophosphamide at 5 mg/kg, and 1 dose of cyclophosphamide at 7 mg/kg (3.2 mg/lb) for a total of 6 doses. At the time of the sixth dose, the patient had progressive leukocytosis (58.3 × 10³ WBCs/μL) and lymphocytosis (46.0 × 10³ lymphocytes/μL). One week later, the patient was returned because of quality-of-life concerns. The patient was lethargic, weak, and dehydrated and had lost 29% of its initial body weight, and euthanasia was elected.

At necropsy, there was marked erythroid and granulocyte hypoplasia in the marrow of the femur, moderate multifocal lymphohistiocytic meningoencephalitis, marked multifocal lymphohistiocytic and heterophilic stomatitis, marked diffuse hepatic lipidosis, moderate multifocal lymphohistiocytic hepatitis, multifocal heterophilic splenitis with moderate diffuse lymphoid depletion, moderate multifocal lymphohistiocytic myositis, and moderate multifocal lymphoplasmacytic interstitial pneumonia. Findings were consistent with widespread inflammation, and immunosuppression and subsequent sepsis were considered the most likely causes of the patient's clinical decline. However, no infectious agents were identified. Survival time (ie, time from initial diagnosis to euthanasia) was 330 days.

A 3-year-old 0.567-kg (1.25-lb) male bearded dragon (bearded dragon 2) was referred for evaluation because of lymphocytosis. The patient had originally been examined by the referring veterinarian 1 week earlier because of a suspected seizure. At that time, a CBC revealed severe leukocytosis (99.9 × 10³ WBCs/μL) and lymphocytosis (89.9 × 10³ lymphocytes/μL). A follow-up CBC performed 4 days later revealed progressive leukocytosis (153.1 × 10³ WBCs/μL) and lymphocytosis (150.0 × 10³ lymphocytes/μL), at which time the patient was referred for further diagnostic testing.

On physical examination, the patient had a dull mentation and generalized weakness as well as an approximately 1-cm-diameter midcoelomic mass on palpation. A CBC revealed progressive leukocytosis (414.0 × 10³ WBCs/μL) and lymphocytosis (393.3 × 10³ lymphocytes/μL), moderate anemia (PCV, 11%; reference range,¹ 17% to 45%), and mild heterophilia (8.3 × 10³ heterophils/μL). A review of the blood smear by a veterinary clinical pathologist confirmed lymphoid leukemia (Figure 1). Selected serum biochemical testing revealed severe hyperglycemia (475 mg/dL; reference range,¹ 108 to 333 mg/dL) and hyperkalemia (> 9 mmol/L; reference range,¹ 1.5 to 7.1 mmol/L). Coelomic ultrasonography revealed bilobed splenomegaly, hepatomegaly with perivascular hyperechogenicity, and a small volume of coelomic effusion. Splenic and hepatic aspirates and a sample of the coelomic effusion were obtained. Cytologic evaluation of all 3 samples provided evidence of lymphoid neoplasia. The patient was given an injection of l-asparaginase (400 U/kg, SC) and was discharged with a prescription for prednisolone (1 mg/kg, PO, q 24 h).

The patient was returned 3 days later because of episodes of increased respiratory effort. A CBC showed substantial improvement in the leukocytosis (112.4 × 10³ WBCs/μL) and lymphocytosis (95.6 × 10³ lymphocytes/μL) with no change in the PCV (11%) and mild heterophilia (7.8 × 10³ heterophils/μL). The patient was given a dose of lomustine (80 mg/m², PO), and treatment with ceftazidime (20 mg/kg [9.1 mg/lb], IM, q 5 d) was initiated. Three weeks later, the leukocytosis (191.0 × 10³ WBCs/μL) and lymphocytosis (177.6 × 10³ lymphocytes/μL) were worse, but the PCV (19%) and heterophil count (5.7 × 10³ heterophils/μL) were within reference limits (Figures 2 and 3). Additional doses of l-asparaginase (400 U/kg, SC) and lomustine (80 mg/m², PO) were given. Two weeks later, the leukocytosis (80.0 × 10³ WBCs/μL) and lymphocytosis (75.2 × 10³ lymphocytes/μL) had improved, but the patient had moderate anemia (PCV, 12%) and relative heteropenia (0.8 × 10³ heterophils/μL) with severe toxic changes. Chemotherapy was not administered.

Graphs of WBC and lymphocyte counts (X 10³ cells/μL) over time in 5 bearded dragons with leukemia. Times when treatments were administered are indicated. A = l-asparaginase administered. C = Cyclophosphamide administered. L = Lomustine administered. P = Treatment with prednisone initiated.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Graphs of WBC and lymphocyte counts (X 10³ cells/μL) over time in 5 bearded dragons with leukemia. Times when treatments were administered are indicated. A = l-asparaginase administered. C = Cyclophosphamide administered. L = Lomustine administered. P = Treatment with prednisone initiated.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Graphs of WBC and lymphocyte counts (X 10³ cells/μL) over time in 5 bearded dragons with leukemia. Times when treatments were administered are indicated. A = l-asparaginase administered. C = Cyclophosphamide administered. L = Lomustine administered. P = Treatment with prednisone initiated.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Graphs of PCV (%) and heterophil counts (X 10³ heterophils/μL) over time in 5 bearded dragons with leukemia. See Figure 2 for key.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Graphs of PCV (%) and heterophil counts (X 10³ heterophils/μL) over time in 5 bearded dragons with leukemia. See Figure 2 for key.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Graphs of PCV (%) and heterophil counts (X 10³ heterophils/μL) over time in 5 bearded dragons with leukemia. See Figure 2 for key.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Four days later, the patient was euthanized because of progressive lethargy and inappetence. At necropsy, infiltrations of large neoplastic lymphocytes were present in the coelomic mass, stomach, liver, small intestine, kidney, testis, lung, skeletal muscle, and fascia, consistent with lymphoid neoplasia. The origin of the coelomic mass could not be confirmed owing to effacement of tissue architecture by neoplastic cells, but the location and ultrasonographic findings were suggestive of a splenic origin. Additionally, lymphoblasts were present in the heart, kidney, brain, liver, lung, stomach, small intestine, and pancreatic vasculature. There was extensive infiltration of neoplastic lymphocytes in the tissues surrounding the right femur. There was replacement of normal hematopoietic tissue by neoplastic lymphocytes with remodeling of the medullary cavity and periosteal new bone formation (Figure 4). The patient's clinical decline was attributed to widespread lymphoid leukemia. Survival time was 57 days.

Photomicrographs of tissue sections obtained from a bearded dragon (bearded dragon 2) at the time of necropsy. Tissues evaluated included a coelomic mass (A), femoral bone marrow (B), kidney (C), and liver (D). The coelomic mass (A) was comprised almost entirely of neoplastic lymphoid cells, with no normal cells or architecture visible; the origin of the mass, therefore, could not be determined. The bone marrow (B) has infiltrations of neoplastic lymphoid cells; the bone itself has normal cellular architecture. The kidney (C) and liver (D) have infiltrations of neoplastic lymphoid cells in the parenchyma, although some normal cellular architecture is maintained. H&E stain; bars = 25 μm (A, B, and C) and 50 μm (D).

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Photomicrographs of tissue sections obtained from a bearded dragon (bearded dragon 2) at the time of necropsy. Tissues evaluated included a coelomic mass (A), femoral bone marrow (B), kidney (C), and liver (D). The coelomic mass (A) was comprised almost entirely of neoplastic lymphoid cells, with no normal cells or architecture visible; the origin of the mass, therefore, could not be determined. The bone marrow (B) has infiltrations of neoplastic lymphoid cells; the bone itself has normal cellular architecture. The kidney (C) and liver (D) have infiltrations of neoplastic lymphoid cells in the parenchyma, although some normal cellular architecture is maintained. H&E stain; bars = 25 μm (A, B, and C) and 50 μm (D).

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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Photomicrographs of tissue sections obtained from a bearded dragon (bearded dragon 2) at the time of necropsy. Tissues evaluated included a coelomic mass (A), femoral bone marrow (B), kidney (C), and liver (D). The coelomic mass (A) was comprised almost entirely of neoplastic lymphoid cells, with no normal cells or architecture visible; the origin of the mass, therefore, could not be determined. The bone marrow (B) has infiltrations of neoplastic lymphoid cells; the bone itself has normal cellular architecture. The kidney (C) and liver (D) have infiltrations of neoplastic lymphoid cells in the parenchyma, although some normal cellular architecture is maintained. H&E stain; bars = 25 μm (A, B, and C) and 50 μm (D).

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.748

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A 1-year-old 0.470-kg (1.03-lb) male bearded dragon (bearded dragon 3) was referred for evaluation because of suspected lymphoid leukemia. The owners had acquired the patient from a rescue organization approximately 6 months earlier and were the same individuals who owned bearded dragon 1. Both bearded dragons lived in the same household for approximately 4 months, although they never had contact with one another. Following the death of bearded dragon 1, bearded dragon 3 was housed in the same cage that bearded dragon 1 had previously inhabited. However, the cage had been disinfected with 5% sodium hypochlorite and terrarium cleaner^a between the 2 inhabitants. The 2 patients were not known to have any genetic relation.

Bearded dragon 3 had initially been examined by the referring veterinarian because of a swollen digit; no intervention was performed at that time. At a recheck examination 1 month later, a second digit was swollen. A CBC revealed moderate leukocytosis (28.7 × 10³ WBCs/μL) with severe lymphocytosis (25.8 × 10³ lymphocytes/μL). Serum biochemical testing revealed hyperuricemia (46.3 mg/dL; reference range,¹ 0.5 to 9.8 mg/dL). The patient was started on ciprofloxacin (11 mg/kg [5 mg/lb], PO, q 24 h) and allopurinol (15 mg/kg [6.8 mg/lb]. PO, q 24 h). Recheck clinicopathologic testing 1 month later revealed progressive leukocytosis (59.4 × 10³ WBCs/μL) and lymphocytosis (52.9 × 10³ lymphocytes/μL) and an improvement in uric acid concentration (9.1 mg/dL). A blood smear was submitted to the University of Florida for immunocytochemical staining for CD3, and results were positive for a low number of lymphocytes. The veterinary clinical pathologist postulated that the low number of positive cells suggested natural killer or B-cell lymphocyte origin; however, additional markers to further investigate the origin were not available. Ciprofloxacin was discontinued, and the patient was started on ceftazidime (30 mg/kg, IM, q 72 h) and referred for additional diagnostic testing.

On initial examination by the Exotic Animal Medicine Service, there was a swelling of the fourth digit of the left thoracic limb and the first digit of the left pelvic limb. A CBC revealed progressive leukocytosis (138.0 × 10³ WBCs/μL) and lymphocytosis (126.9 × 10³ lymphocytes/μL). A veterinary clinical pathologist reviewed the blood smear and confirmed the diagnosis of lymphoid leukemia (Figure 1). Serum biochemical testing revealed a mild increase in uric acid concentration (11.9 mg/dL). A blood sample was submitted for testing with a pan-herpesviral PCR assay targeting a conserved region of the DNA polymerase gene,^2,3 but results were negative. Whole-body radiography and coelomic ultrasonography did not show evidence of neoplasia.

The patient was started on the same protocol of l-asparaginase, prednisolone, and lomustine and achieved partial remission. A total of 8 doses of lomustine (80 mg/m², PO) were given at approximately 3-week intervals. The longest interdose interval was approximately 3 months and occurred between the seventh and eighth doses because of relative heteropenia (1.6 × 10³ heterophils/μL) and owner unavailability (Figure 2). At a recheck examination 8 weeks after the eighth dose of chemotherapy, the WBC and lymphocyte counts were slightly increased (24.0 × 10³ WBCs/μL and 20.9 × 10³ lymphocytes/μL). However, there was severe hyperuricemia (46 mg/dL); therefore, fluids (lactated Ringer solution, 15 mL/kg, SC, 3 times weekly) were administered, and daily soaks and allopurinol (15 mg/kg, PO, q 24 h), which the owners had not been giving regularly, were started. The patient was euthanized approximately 1 month later because of progressive lethargy and inappetence. Necropsy revealed evidence of visceral and articular gout, and severe articular and renal accumulations of uric acid crystals, consistent with gout, were found on histologic examination. The heart, lung, spleen, pancreas, gastrointestinal tract, and bone marrow were histologically unremarkable. Time from diagnosis to euthanasia was 416 days.

A 5-year-old 0.393-kg (0.86-lb) female bearded dragon (bearded dragon 4) was examined because of severe lymphocytosis. Four weeks earlier, the owner had noticed weight loss and a reduction in appetite. A CBC, serum biochemical panel, and protein electrophoresis were performed, and there was marked leukocytosis (140.0 × 10³ WBCs/μL) characterized by lymphocytosis (135.8 × 10³ lymphocytes/μL) and high β-globulin (3.34 g/dL; reference range,¹ 0.92 to 2.5 g/dL) and γ-globulin (1.88 g/dL; reference range,¹ 0.22 to 0.98 g/dL) concentrations. The patient was referred for further diagnostic testing.

On initial examination by the Exotic Animal Medicine Service, the patient was noted to be weak and dehydrated with extreme muscle wasting. A CBC revealed leukocytosis (91.3 × 10³ WBCs/μL) characterized by lymphocytosis (84.9 × 10³ lymphocytes/μL), a normal heterophil count with moderate toxic changes (5.5 × 10³ heterophils/μL), and mild anemia (PCV, 24%). A veterinary clinical pathologist reviewed the blood smear and confirmed the diagnosis of lymphoid leukemia (Figure 1). Whole-body radiography and coelomic ultrasonography showed no evidence of disease.

The patient was treated with lomustine (80 mg/m², PO) but was not given l-asparaginase because of a manufacturing shortage. The patient was discharged with ceftazidime (20 mg/kg, IM, q 72 h) and prednisolone (1 mg/kg, PO, q 24 h). The patient was returned 4 weeks later and was reported to be lethargic and have a poor appetite. The patient had lost 20% of its body weight and was moderately dehydrated. A CBC revealed progressive leukocytosis (118.6 × 10³ WBCs/μL) and lymphocytosis (115.0 × 10³ lymphocytes/μL). No toxic heterophils were seen, and the PCV was within reference limits (27%); however, given the patient's dehydration, hemoconcentration was suspected to be masking some degree of anemia. The patient was treated with a second dose of lomustine (80 mg/m², PO) and an injection of l-asparaginase (400 U/kg, SC). At a recheck evaluation 4 weeks later, the patient had an improved appetite and energy level and normal hydration with no further weight loss. A partial remission had been achieved with improvements in leukocytosis (44.5 × 10³ WBCs/μL) and lymphocytosis (40.9 × 10³ lymphocytes/μL; Figures 2 and 3). At the time of final follow-up, the patient had received 5 doses of lomustine and was still in partial remission with a steady decrease in lymphocyte count at each visit. Doses of lomustine had been given at approximately 4-week intervals, with one 17-week interval due to a persistent heteropenia (nadir of 0.9 × 10³ heterophils/μL). The lowest lymphocyte count achieved was 1.1 × 10³ lymphocytes/μL (Figure 2). The patient was still alive 244 days after the initial diagnosis.

A 2-year-old 0.313-kg (0.69-lb) female bearded dragon (bearded dragon 5) was examined because of severe lymphocytosis. The patient had been examined 1 month earlier because of a 3-day history of anorexia. A CBC, serum biochemical panel, and protein electrophoresis were performed, and there was a high-normal WBC count (17.2 × 10³ WBCs/μL) with moderate lymphocytosis (16.7 × 10³ lymphocytes/μL) and marked hypoalbuminemia (0.27 g/dL; reference range,¹ 2.0 to 4.1 g/dL). Three weeks later, a follow-up CBC revealed moderate leukocytosis (33.0 × 10³ WBCs/μL) and marked lymphocytosis (31.0 × 10³ lymphocytes/μL), at which time the patient was referred.

On physical examination, the patient was emaciated and dehydrated. A CBC was performed and showed progressive leukocytosis (73.3 × 10³ WBCs/μL) with lymphocytosis (66.7 × 10³ lymphocytes/μL), monocytosis (4.4 × 10³ monocytes/μL), and moderate anemia (PCV, 8%). A veterinary clinical pathologist reviewed the blood smear and confirmed the diagnosis of lymphoid leukemia (Figure 1). Full staging was declined by the owner.

The patient was treated with lomustine (80 mg/m², PO) but was not given l-asparaginase because of a manufacturing shortage. The patient was discharged with ceftiofur crystalline free acid (30 mg/kg, SC, q 10 d) and prednisolone (1 mg/kg, PO, q 24 h). The owner reported an initial improvement in the patient's energy level and appetite. However, the patient began having bowel movements that resembled melena. Gastroprotectant medications such as omeprazole and sucralfate were recommended but not pursued, and the owner discontinued all medications after a few weeks. After cessation of medications, the patient was reported to regurgitate occasionally and had intermittent dark stools. The owner elected not to proceed with further treatment; however, a CBC performed by the referring veterinarian 76 days after the single dose of lomustine indicated partial remission with improvements in the leukocytosis (38.0 × 10³ WBCs/μL), lymphocytosis (22.8 × 10³ lymphocytes/μL), and monocytosis (3.0 × 10³ monocytes/μL). Anemia (PCV, 11%) was diagnosed at that time. The patient was continuing to eat but appeared to be passing minimally digested feed material and had lost 14% of its body weight. The patient was euthanized by the referring veterinarian approximately 10 weeks later owing to quality-of-life concerns. Samples were submitted for histologic examination, which showed mild multifocal tubular ectasia, degeneration, and necrosis of the kidneys. No overt neoplastic cells were seen. Survival time was 157 days.

Discussion

Although there are many individual accounts of neoplasia in bearded dragons,^{4,5,6,7,8,9,10,11,12} the overall prevalence is unknown. A 2004 retrospective survey¹³ reported that the overall prevalence of neoplasia in reptiles may be as high as 9.9%. A 2017 review article¹⁴ suggested that it could be even higher, up to 26%. There have been several reports^{5,10,11,12,15,16} of bearded dragons with leukemias, at least 4 of which were lymphoid in origin. In only one of these reports,⁵ a bearded dragon with monocytic leukemia, was treatment attempted. The patient received cytosine arabinoside IV over 48 hours and died suddenly at hour 44 of the treatment. A study¹⁷ evaluating the incidence of lymphocytosis and lymphoid leukemia from submissions of bearded dragon blood smears suggests that this species may be predisposed to lymphocytosis and subsequent neoplastic transformation. Because this disease may be more common than previously thought, more information is needed to aid in its diagnosis and treatment.

The patients in the present report all had nonspecific clinical signs, including poor appetite, lethargy, and weight loss. Bearded dragon 1 initially was examined because of ocular signs, which may have been an unrelated problem or could have been due to ocular or periocular lymphoid neoplasia that responded to topical prednisone treatment. Bearded dragon 3 initially was examined because of swollen digits; however, this was suspected to have been caused by gout secondary to severe hyperuricemia, although infiltration of neoplastic cells into the digits could not be ruled out.

A CBC and serum biochemical testing were performed in all patients. The characteristic hematologic finding in all patients was marked, progressive lymphocytosis. Review of the blood smears by a veterinary clinical pathologist was crucial for distinguishing the lymphocytes as neoplastic. Cells were similar in morphology and described as intermediate to large lymphocytes with round to indented nuclei, finely stippled chromatin, and occasional nucleoli; mitotic figures were sometimes seen. Additional hematologic and biochemical abnormalities seen in these patients included anemia (n = 3), heterophilia (2), monocytosis (2), hyperglycemia (1), hyperkalemia (1), hypoalbuminemia (1), and hyperuricemia (1). Platelet count could not be accurately quantified in these patients; however, platelets were deemed adequate in all patients at all times on the basis of blood smear review. Protein electrophoresis was performed on 1 patient and revealed high β- and γ-globulin concentrations. Immunocytochemical testing was performed on 1 patient and yielded inconclusive results. In a previous report¹⁵ of a bearded dragon with lymphocytic leukemia, results of immunocytochemical staining of blood smears were negative for CD3 and positive for CD79a, indicating B-cell leukemia. Further investigation into the immunophenotyping of these leukemias is warranted. For the present report, there was concern about possible antigen degradation, because saved blood smear slides were up to 13 months old and had not been stored specifically for immunohistochemical testing; therefore, this test was not performed.

Additional staging was performed in 4 of 5 patients described in the present report. Coelomic ultrasonography was performed in 4 patients, and whole-body radiography was performed in 2. Only bearded dragon 2 had evidence of systemic disease, which was palpable during a physical examination and confirmed cytologically as well as histologically at necropsy. This patient also had evidence of neoplastic infiltration into multiple tissues on postmortem examination.

Little information exists on chemotherapy in reptiles,^{14,18,19,20,21} and administration of chemotherapeutic agents in reptiles is hindered by a lack of knowledge regarding efficacy, toxicity, and pharmacokinetics. Obtaining repeated IV access is also a challenge in reptiles. Therefore, some drugs commonly used in the treatment of lymphoid neoplasia, such as doxorubicin, that are associated with substantial adverse effects when extravasation occurs carry even greater risk in these species.²² A vascular access port was considered; however, owing to the technical challenges of placing one in an animal the size of a bearded dragon, the decision was made to use only chemotherapeutic agents that could be given orally.

The primary chemotherapeutic agent used in all 5 patients described in the present report was lomustine, an alkylating nitrosurea compound. Lomustine functions by transferring the chlorethyl group of nitrosurea to the O-6 methyl group of guanine on DNA, causing DNA cross-linking, inactivation of DNA synthesis, and cell death.²² This medication has high oral bioavailability and high membrane penetration due to its lipophilicity and has been shown to have potential efficacy with low rates of toxicosis in humans with acute myeloid leukemia. Lomustine is also commonly used in rescue protocols for dogs with lymphoma.^22,23 Additionally, it can be used as a single agent, which was desirable for our patients.

One challenge in determining the appropriate dose of lomustine for bearded dragons is that the dose of lomustine is conventionally calculated on the basis of body surface area. At this time, an accurate shape constant for calculating body surface area of bearded dragons is unknown. Therefore, an estimated K value of 11 was used on the basis of allometric scaling recommendations from empirical experience in reptiles.²⁴ Patients were treated at the standard dose of lomustine for dogs (80 mg/m²) at approximately 3- to 4-week intervals with regular CBC monitoring to aid in assessing the dosing regimen. All patients were treated with a liquid lomustine preparation (5 mg of lomustine/mL) that was compounded by pharmacists at North Carolina State University. This solution was compounded by combining the contents of a 10-mg capsule of lomustine with 1 mL of suspending vehicle^b and 1 mL of a sweetening vehicle.^c Stability data for this compound have not been determined, but the formulation was considered stable for 14 days under refrigeration on the basis of US Pharmacopeia recommendations for water-based suspensions.²⁵

Cyclophosphamide, an alkylating agent, was chosen as the rescue agent for bearded dragon 1 after relapse. Cyclophosphamide is a prodrug that is metabolized by the liver to the active metabolite phosphoramide mustard, which causes cross-linking of DNA, leading to cell death in mammals.²² Although conversion of cyclophosphamide to this active metabolite has not been demonstrated in reptiles, clinical efficacy suggests a conserved mechanism across mammalian and reptilian species. This drug was chosen because it can be administered orally and is part of the standard protocol used to treat dogs and cats with lymphoma.²² Additionally, there is little cross-resistance among alkylating agents, making this drug a reasonable choice for rescue treatment.²⁶ The initial dose (3 mg/kg) was extrapolated from a reported modified cyclophosphamide, doxorubicin, vincristine, and prednisolone protocol used in the treatment of lymphoma in a green iguana.²⁷ This is approximately a third of the standard dose used in dogs, accounting for the slower metabolic rate in reptiles.²² Because the dose was well tolerated and the patient's lymphocyte count increased after 2 doses, the dose of cyclophosphamide was increased to 5 mg/kg for 2 doses and then to 7 mg/kg for 1 dose before the patient's condition declined. The dosing interval of 7 to 10 days was based on comparable intervals used in cats and dogs.²²

Lomustine was clinically well tolerated in 4 of the 5 patients in the present study. The owner of bearded dragon 5 reported adverse effects, including gastrointestinal upset and possible melena, following a single dose of lomustine; however, it could not be determined whether these occurred secondary to chemotherapy or disease progression. The most common adverse effect of lomustine was relative heteropenia (defined as a heterophil count < 2.0 × 10³ heterophils/μL), which was seen in 3 patients. Although this value is higher than the lower reference limit¹ (0.24 × 10³ heterophils/μL), it represented a substantial decrease from the initial count in all patients, and patients with a count below this threshold did not receive chemotherapy. This protocol was in accordance with similar protocols based on neutrophil counts used in mammalian chemotherapy.²² These recommendations, however, are largely anecdotal and have been subject to dispute.²⁸ Only bearded dragon 2 was reported to be clinically ill at the time of relative heteropenia and was euthanized shortly thereafter. Necropsy findings were consistent with widespread infiltration of neoplastic disease rather than secondary infection from myelosuppression. Bearded dragon 3 was found to have histologic changes consistent with gout on necropsy. Although it is possible that this could have been secondary to lomustine administration, it is thought to be less likely given that the patient had a preexisting history of high uric acid concentration and that lomustine is metabolized primarily by the liver. No evidence of neoplasia was detected on necropsy of bearded dragon 3.

Cyclophosphamide was initially well tolerated in the 1 patient that received this medication. However, the patient became suddenly worse after the sixth dose, and necropsy findings were consistent with myelosuppression and potential sepsis. It is suspected that this was caused by cyclophosphamide, although the heterophil count was normal prior to euthanasia. Immunosuppression may have been due to the cumulative effect of the medication or to the fact that the last doses (7 mg/kg given 11 days apart) exceeded the maximum tolerated dose in this species. More information is needed; however, our findings suggested that this medication should be used with caution, especially at higher doses.

All patients described in the present report were given 1 or 2 doses of l-asparaginase (depending on availability of the drug) as an induction agent in accordance with guidelines for treatment of lymphoma in cats and dogs.²⁰ The patients were also treated with prednisolone at a dosage of 1 mg/kg, PO, every 24 hours. This dosage was extrapolated from the dosages recommended for the treatment of lymphoid leukemia in dogs and cats and the lymphotoxic properties of prednisone in several species.^{13,14,18,19,20,21,27} In bearded dragon 1, treatment with prednisolone alone for 10 days resulted in an almost 75% reduction in the total number of lymphocytes. Because this medication was well tolerated in all patients, we recommend it as an adjunct to chemotherapy or as a sole agent if palliation is elected.

Patients in the present report were also treated with antimicrobials in an attempt to prevent infections secondary to myelosuppression. No clinical infections were noted throughout the course of chemotherapy in any of these 5 patients, although sepsis secondary to immunosuppression was suspected on the basis of necropsy findings for bearded dragon 3. Survival times for the 5 patients ranged from 57 to 416 days, with 1 patient alive and receiving treatment at the time of final follow-up.

The relatively high number of patients in which lymphocytic leukemia was diagnosed at our hospital during the 13-month period raises questions about the etiology of the disease, with environmental, toxic, genetic, and infectious causes considered. All patients in this report lived in North Carolina, although their residences were scattered throughout the state, aside from the 2 that lived in the same household. No toxins were identified in any of the households, and the household with 2 affected patients housed several other unaffected bearded dragons. No genetic link was established between patients, as all were adopted rather than acquired from a breeder. However, this does not rule out the possibility that the patients were genetically related, because genetic testing was not performed. An infectious cause was considered and investigated with a pan-herpesviral PCR assay in bearded dragon 3, but results were negative. Lymphoid neoplasia has been associated with retroviruses in mammals but not in reptiles.^29,30 Nevertheless, a retrovirus could be a possible infectious cause of this disease, and further testing is indicated. Additional research is needed to determine median survival times with and without treatment, obtain pharmacokinetic data for chemotherapeutic drugs, derive body surface area formulas, and assess the utility of injectable chemotherapeutics.