Ehrlichia canis in a dog with large granular lymphocytosis, thrombocytopenia, and dysproteinemia
Ehrlichia canis in a Dog with Large Granular Lymphocytosis, Thrombocytopenia, and Dysproteinemia Omega CantrellINTRODUCTIONCanine monocytic ehrlichiosis (CME) is caused by Ehrlichia canis, a Gram-negative obligate intracellularcoccus bacterium. The organism is transmitted by the brown dog tick, Rhipicephalus sanguineus, whichis infected transstadially (via a blood meal from an infected dog) when the organism is in either thelarvae or nymph form. It then transmits the bacterium to an uninfected dog when the organism is ineither the nymph or adult form. E. canis targets monocytes, in which it replicates and forms a morula,but can be difficult to visualize on cytological samples. As a result, various serological tests, includingIFA, PCR, and/or Western blot are often used as diagnostic tools in the absence of the demonstration ofthe organism using cytology. CME has various presentations, including acute, subacute, and chronicphases. A common finding amongst all is thrombocytopenia, believed to be mediated by platelet-associated IgG and antibodies that recognize platelet proteins in dogs infected with E. canis. Likewise,hyperglobulinemia, hypoalbuminemia, and a polyclonal gammopathy may be seen in affectedindividuals. In chronic forms of the disease, bone marrow suppression may be seen, resulting inpancytopenia and hemorrhage. Dogs in the early stages of disease may have a CBC which demonstrateslymphocytosis with cell granularity typical of lymphocytic leukemia. Treatment consists of tetracycline ordoxycycline, and improvement of thrombocytopenia is used as an indicator of successful treatment.PATIENT HISTORY AND PHYSICAL EXAMINATION FINDINGSA 7-year old, spayed female, mixed breed dog presented to the Kansas State University VeterinaryTeaching Hospital for evaluation of an episode of epistaxis which lasted approximately 24 hoursfollowing blunt trauma. Epistaxis had ceased approximately 12 hours prior to presentation, but it wasnoted in the animal’s history that a previous incident of mild, self-limiting epistaxis had occurred about 2
weeks prior to presentation. Ticks had been noted on the animal several months prior, though none hadbeen noted in the previous five months. The referring veterinarian noted thrombocytopenia,lymphocytosis, azotemia, and hyperproteinemia, and referred the animal to KSU-VTH’s oncology serviceto confirm a suspected case of lymphocytic leukemia.On physical examination, all findings were normal, with the exception of a small amount of dried bloodnoted in the nares. For further evaluation, CBC, serum biochemistry, urinalysis, and abdominalradiographs were performed. To rule out any possible neoplastic causes for the abnormalities noted onlaboratory findings, a bone marrow aspiration was obtained, as well as antibody titers to severalcommon tick-borne diseases, due to the animal’s prior exposure to ticks.LABORATORY TEST RESULTSCBCParameter Value RangeWhite blood cells (WBC) 18.0 x 103/µL 6.0-17.0 x 103/µLLymphocytes 13.0 x 103/µL 1.5-5.0 x 103/µLPlatelets (PLT) 8.0 x 103/µL 200-500 x 103/µLPacked cell volume (PCV) 30.4% 37.55%Abnormalities (peripheral blood smear)Large granular lymphocytes (LGLs) 50% 0-10%Serum biochemistryParameter Value RangeTotal protein (TP) 13.5 g/dL 5.6-7.9 g/dLGlobulin 11.4 g/dL 1.8-4.2 g/dLAlbumin 2.1 g/dL 3.09-4.5 g/dLSerum urea nitrogen (SUN) 90 mg/dL 8-30 mg/dLCreatinine 2.9 mg/dL 0.5-1.4 mg/dLUrinalysisParameter ResultsUrine specific gravity (USG) 1.015Blood 3-8 RBCs/HPFProtein 3+
Antibody titersOrganism tested for (IgG reaction) ResultBorrelia burgdorferi NegativeRickettsia rickettsii NegativeEhrlichia canis Positive (1:2048)Serum protein electrophoresisParameter Value Rangeβ-globulin 2.8 g/dL 1.3-2.7 g/dLγ-globulin 6.4 g/dL 0.9-2.3 g/dLBone marrow aspirationParameter Value RangePlasma cells 2.5% <2%Lymphocytes <1% <1%Other: mild erythroid hyperplasia, decreased megakaryocytes notedFlow cytometryParameter Value RangePlatelets with surface IgG reactivity 23% 0-14%INTERPRETATION OF RESULTSOn laboratory evaluation, both leukocytosis and lymphocytosis were noted, as well as a severethrombocytopenia and mild anemia. A peripheral blood smear was performed using Wright’s stain, atwhich time no leukocyte- or hemoparasites were noted. Approximately 50% of lymphocytes (200evaluated) were found to be large granular lymphocytes. Serum biochemistry showedhyperproteinemia, hyperglobulinemia, and hypoalbuminemia, as well as increased serum urea nitrogen(SUN) and creatinine. Urinalysis showed hematuria and proteinuria, as well as a USG of 1.015, suggestiveof glomerular proteinuria.Due to the patient’s history of exposure to ticks, antibody titers were performed to rule out Lymedisease, Rocky Mountain Spotted Fever, and Ehrlichia as possible causes of laboratory abnormalities.Both titers for B. burdorferi (Lyme) and R. rickettsii (RMSF) were negative, but the titer for E. canis was
positive at 1:2048 (positive test is >1:128). PCR for E. canis using a whole blood sample was performed,but was negative. Serum protein electrophoresis show a mild increased in β-globulin, as well as anincrease in γ-globulin, indicating the presence of a polyclonal gammopathy in the patient.Using flow cytometry, it was noted that 23% of platelets had surface reactivity to IgG, indicative of animmune-mediated thrombocytopenia. A bone marrow aspiration, thoracic radiographs, and abdominalultrasound were also performed to rule out the possibility that a neoplastic process was responsible forthe laboratory abnormalities. Upon evaluation of the bone marrow aspirate, a mild erythroidhyperplasia was noted, as well as decreased megakaryocyte and increased plasma cell counts.Lymphocyte count was within normal limits. Thoracic radiographs were unremarkable, but ultrasoundrevealed hyperechogenicity at the renal cortices, indicative of possible glomerulonephritis oramyloidosis.DISCUSSIONWhile the animal was referred on the basis of suspected neoplasm, a large granular lymphocyticleukemia was unlikely due to the presence of hyperglobulinemia, thrombocytopenia, and suspectedglomerulonephritis. This, in conjunction with the absence of fever and a history of tick exposure, suggesta case of chronic canine monocytic ehrlichiosis (CME). Upon performing antibody titers for common tick-borne diseases, a strongly positive (1:2048) result for Ehrlichia canis was noted. Despite a negative PCRusing whole blood for E. canis, it is still believed that the patient was suffering from ehrlichiosis, with thebelief that the PCR was negative due to possible sequestration of the organism in the spleen or othersites in the body.Due to this suspicion, the animal was treated using doxycycline at a dose of 6 mg/kg, given PO q12h, aswell as prednisone at a dose of 2 mg/kg, given PO q24h. At a 2-week recheck, CBC showed that theanemia as well as leuko- and lymphocytoses had resolved, and the count of large granular lymphocytes
had decreased to 10% (normal 0-10%). Thrombocytopenia was still present, though platelet numbershad increased (to 45.0 x 103/µL, normal 200-500 x 103/µL), suggesting that the issue was resolving. As aresult, treatment with doxycycline was continued for another two weeks, and prednisone was continuedfor one week at a dose of 1 mg/kg, given PO q24h, after which both were ceased.At a 4-week recheck, all CBC values had returned to normal. Serum biochemistry showed that azotemiawas still present, but resolving (SUN = 77 mg/dL, creatinine = 2.2 mg/dL). Additionally, hyperproteinemia(10.1 g/dL), hyperglobulinemia (7.5 g/dL), and hypoalbuminema (2.6 g/dL) were still present, butresolving. At this time, an increase in ALT (576 U/L, normal 13-79 U/L) and increased ALP (390 U/L,normal 12-122 U/L) were noted. The owner declined further evaluation of the liver, and no urinalysiswas performed at this time. The antibody titer for E. canis was performed again, and was still positive at1:2048, though flow cytometry showed only a 10% platelet surface reactivity to IgG, which could be theresult of the increased total platelet concentration (dilutional effect). Several months later, the patientwas still doing well.REFERENCESBockino, Lauren, PM Krimer, KS Latimer, and PJ Bain. An Overview of Canine Ehrlichiosis. Available:http://www.vet.uga.edu/vpp/clerk/Bockino/. Last accessed 3 December 2011.Ehrlichiosis. Available: http://www.vetmed.wisc.edu/pbs/zoonoses/Ehrlichia/ehrcanisdogs.html. Lastaccessed 3 December 2011.Heeb, Heather L., MJ Wilkerson, R Chun, RR Ganta. (2003). Large Granular Lymphocytosis, LymphocyteSubset Inversion, Thrombocytopenia, Dysproteinemia, and Positive Ehrlichia Serology in a Dog. Journalof the American Animal Hospital Association. 39 (1), 379-384.Peters, Jeanine. (2000). Canine Ehrlichiosis. Available:http://www.addl.purdue.edu/newsletters/2000/winter/ce.shtml. Last accessed 3 December 2011.